| Brett |
| quote: | Originally posted by RockysDad
Anyone know of a proven designs using the EL84s either in pentode or triode mode? There are too many designs out there and I wanted to find a few designs that have been built and heard.
Also, is there a particular driver tube that sound good with the EL84? |
Build a circuit design with the '84 in triode or pentode at 250V B+, and play with a variety of different driver tubes. Pull the op points off the Mullard datasheet. This is the easiest power tube to drive well. Almost anything except a 12AX7 will do, just because they stink so bad. try 12AU7, 6SN7, ECC99, 6FQ7 etc and find the flavour you like best.
It's really easy, and if you do it from scratch you'll learn a LOT more than simply building another person's design. The Grounded Cathode Tube article on Tubecad explains how to do it (for the driver and the Mullard sheet tells the '84 pent and tri op points.
Unless you use NFB, a pentode will have a very high output Z, which might not ba a problem if you use a low Q driver like a Fostex.
Blech. The EL34 is a different animal. |
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| RockysDad |
| quote: | | Blech. The EL34 is a different animal. |
Oh, wow.. Brain freeze...:xeye:
| quote: | | It's really easy, and if you do it from scratch you'll learn a LOT more than simply building another person's design. The Grounded Cathode Tube article on Tubecad explains how to do it (for the driver and the Mullard sheet tells the '84 pent and tri op points. |
Is it? I read that article some time ago but never fully understood whats going on. Also, I never figure out how the driver and power sections work together. That where I sort of left off but maybe I'll try and reading it again. Maybe this time I will understand it better since Il have a project in mind when I read it. Wish me luck. I know I will have questions though...
Thanks... |
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| audiousername |
| quote: | Originally posted by Brett
Blech. The EL34 is a different animal. |
Exactly. The things which the EL34 shares with the EL84 are:
- 6.3V heater (E)
- Output beam tetrode/pentode (L)
| quote: | Originally posted by Brett
It's really easy, and if you do it from scratch you'll learn a LOT more than simply building another person's design. |
Agreed as well. And it's much more satisfying!
Some other links for basics:
Diyparadise
Steve Bench (go to the "Of Loadlines Power Output and Distortion" series.
If you need help, ask!
Sorry, that was a bit of a me-too post...
EDIT: Oh, I see you posted while I was typing... :) |
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| Brett |
| quote: | Originally posted by RockysDad
Is it? |
Yes.| quote: | | I read that article some time ago but never fully understood whats going on. Also, I never figure out how the driver and power sections work together. That where I sort of left off but maybe I'll try and reading it again. Maybe this time I will understand it better since Il have a project in mind when I read it. Wish me luck. I know I will have questions though... |
It's best to learn with a specific application in mind.
I had a guy recently ask me about tubes and wanted to learn, so we set the specs for a project (guitar amp) and it's progressing from there as he can see the direct relationships between the theory and practice as me just explaining the dry theory wasn't getting anywhere.
| quote: | Originally posted by audiousername
If you need help, ask! |
Yep.
Re-read the tubecad article, pick a driver from the list I gave above, try some values for anode and cathode resistors, post them and get a critique.
To simplify it, I think you should try a triode design first (o/p impedance issues), so the Mullard specs are
Vanode = 250V
Ianode = 34mA
Vgrid = -9V
Rload = 3500 ohms
Rcathode = 270 ohms
Power = 1.5W (enough?)
Assume the B+ for the driver will 250V too and work from there.
Buy cheap and/or surplus parts (and resell them to finance the next project) and use this as a learning exercise. |
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| GeirW |
Gday.
@RockysDad.
Regarding 84SE, i think you should look at the SE 1. & 2.
at bonavolta. The same schematics can also be seen at
http://www.tubebuilder.com/schematic2.html
where the design with EEC82 seem to be rated better.
Yesterday, i did come by another one, with ECL86
(can`t remember where)
but this one was givin 5.7W, pretty much the max. for EL84
at 250. I think that one have to much ditortion.
Haven`t a clue about the one at
http://www.tubeaudio.8m.com/RH84/rh84.html
looks interesting though. |
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| audiousername |
The schematics GeirW referred to all have the EL84 operating in pentode mode, which (as Brett has already eluded to) may well cause output impedance issues (though the importance of this will depend on your speakers).
Since suggestions are coming... I might add the Decware Zen to the list. The schematics are there somewhere on the Decware site, and it will have lower distortion and lower output impedance than running the EL84 in pentode mode (and lower power). Oh, and of course it's a proven design. Yes, it uses the SV83 but could probably be easily modified for EL84s, or you could just buy some SV83s.
Still won't beat the satisfaction from designing AND building something yourself from scratch though... ;) |
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| GeirW |
Gday.
This ZEN amp looks interesting.
Low part count, cheap tubes, simple design.
@AUN. do you know the component values,
(small pic./bad eyes.)
btw. is the psu there to.
:) |
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| audiousername |
AUN? I assume that's me. Don't like the name but typed it in without thinking at sign-in... What can you do...
Save the schematic to file and zoom in with Acrobat Reader ;)
Not sure what the OPT primary Z is. I remember reading somewhere that it is very high (like 9K8), which would be consistent with SD's claim of increasing power with lower impedance speakers.
Anything else, just ask.
BTW: Decware sells kits for the Zen with all the parts (inc the transformers, whose specs aren't listed on the schem) for US$399.
EDIT: If you want to see how hard it is to assemble, there is a detailed step-by-step instruction manual here. |
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| GeirW |
Gday.
| quote: |
Save the schematic to file and zoom in with Acrobat Reader |
The only shematic i found was a .gif
What do you mean.:smash: am not quite awake yet.
Edit/
>Google is your friend< |
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| RockysDad |
Okay, I think I'm up for it or at least willing to give it a try. Right now I have a single 12BH7A which I think is similar to a 12AU7. Therefore, this is what I will start with. So, with a 12BH7A being a dual triode I'll use one section for each channel going to an EL84 in triode mode. Nothing fancy here but just a simple SE design. Also, I've been using SS rectifiers till now but maybe I switch to tube, maybe a 5U4, 5Y3 or something similar.
Does this sound like a good start? I 'll try to reread the Tubecad article and will ask a few basic questions as time goes on. Wish me luck. I'll make a new post when I ready... |
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| Brett |
| quote: | Originally posted by RockysDad
Okay, I think I'm up for it or at least willing to give it a try. Right now I have a single 12BH7A which I think is similar to a 12AU7. Therefore, this is what I will start with. So, with a 12BH7A being a dual triode I'll use one section for each channel going to an EL84 in triode mode. Nothing fancy here but just a simple SE design. Also, I've been using SS rectifiers till now but maybe I switch to tube, maybe a 5U4, 5Y3 or something similar.
Does this sound like a good start? I 'll try to reread the Tubecad article and will ask a few basic questions as time goes on. Wish me luck. I'll make a new post when I ready... |
Sounds good.
Luck. |
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| audiousername |
Yes, read John Broskie's article again. It's quite good.
I have quickly drawn something which you may or might not find useful ;) Basically I am trying to show how the grounded cathode amplifiers join together to form an amp.
Everything to the left of C2 is the grounded cathode amplifier input/driver stage (with the 12BH7), and everything to the right of it is the grounded cathode amplifier output stage (with the EL84).
In the schematic, you will see R3 as the plate load resistor for the 12BH7, R2 as the cathode resistor (for self-bias) and C1 as the cathode bypass resistor (optional). R4 is the grid leak resistor, and R1 is a gridstopper (aimed at kiling parastic oscillations).
Basically the same things are present in the output stage. You will recognise R5, R6, R7 and C3 in the same setup (and performing the same function) as R1, R4, R2 and C1 in the first stage respectively.
C2 is the coupling capacitor, it's purpose is basically to stop DC from reaching the EL84's control grid, while passing the AC signal.
R8 is a resistor (I don't know what it's called) which is aimed at preventing oscillation, and limiting the screen current. I believe the connection between the suppressor grid and the cathode is made internally on the EL84, but it probably wouldn't hurt to make it externally.
The output transformer, T1, takes the place of the plate load resistor for the output stage.
The grids of the pentode are numbered from the cathode to the plate. so g1 is known as the control grid, g2 is the screen grid, and g3 is the suppressor grid.
Valve pins are numbered starting from the key/gap in the base, clockwise from the bottom view.
A few words on sizing of components:
After reading and understanding the article, you should be able to calculate the values of the plate load resistor and cathode (self-bias) resistor for a given B+ and operating point.
Grid leak resistors (R4 and R6) are generally sized as large as possible (check the datasheets for the 12BH7 and EL84), to prevent reduction in gain of the preceeding stage. Note that in AC terms, R6 is in parallel with R3.
Gridstoppers (R1 and R5) are sometimes not required. Usually, if required the value is determined experimentally. Common values are between about 100 ohm and a few kOhm.
C2 must be sized such that the low frequency cutoff the RC combination of C2 and R6 does not affect the audio band. As such, the value of C2 (in Farads) is 1/(2*pi*F*R6) where F is the -3dB point required.
C1 and C3 are cathode bypass capacitors, and will also introduce a low-frequency cutoff if used. The calculation of this value is a little involved, so bear with me. The cathode bypass capacitor (C1 or C3) sees the self-bias resistor (R2 or R7) in parallel with the resistance looking into the cathode of the valve (kind of like the plate of the 12BH7 seeing R3 and R6 in parallel). Thus, we can apply the same formula we used to size C2, where the required capacitance was 1/(2*pi*F*R), however the value of R now must be calculated.
Now, the resistance looking into the cathode of a valve is (RL+Ra)/(mu+1), where RL is the plate load resistor, in this case R3, Ra is the plate resistance of the valve (you will need to get this from the datasheet), and mu is the amplification factor of the valve (also from the datasheet). This is in parallel with the cathode resistor R2. So the value or R stated in the paragraph above is composed of these two in parallel (add the values as resistors in parallel and substitute into the formula)
On the -3dB point to choose, some designers choose 1Hz, some choose something higher like 5Hz. As long as it's low, it shouldn't be too critical. (The bandwidth of the OPT will almost certainly limit the frequency response of the amplifier).
Geez, this is a long post... I started writing and couldn't stop! Don't worry it it doesn't make any sense. It will after some time. Read the Broskie article, and download the datasheets for the 12BH7 here (that's the sheet for the 12BH7-A, but don't worry, the difference is in the heater warm-up time) and EL84 here.Those were links to pages on Frank Phillipse's websites (which ought to get some sort of award :smash: )
Hmm... I don't know what to say anymore (A very good thing ;) )
Good luck! |
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| RockysDad |
Audiousername, thanks for the writeup and schematic! I was thinking along the same line as far as a design goes. Just your typical RC coupled SE design is probably the best place to start if you are a beginner, I suppose. Then once everything works and a baseline can be established then tweeking can take place.
I've been through this with the Foreplay preamp I built awhile back. The same philosophy of enjoying the journey vs. just getting to the destination is the same. But this time some bookwork has to take place which requires a little more disipline and time. The part I am trying to figure out now is dealing with the load lines. I'm still having trouble trying to understand how the voltage swings vs. current available and how distortion is being calculated. I need to try a few more examples and maybe it will sink in then. But I will try to fill in most of the blanks from your writeup and will ask more detailed questions later. So thanks again and now back the my articles... |
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| GeirW |
Gday.
@RockysDad.
Do you have plotted in the values on the 12BH7-84 schem,
RD. Can you post them here.
First i was going to replicate a Tanberg 84 design,
but for several reasons, have now totally forgot that project.
I still have some spare parts, that should go along fine
with this amp.
:) |
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| planet10 |
The Decware Zen is really quite good... we have gotten to calling clones "Mulligans"
dave
planet10/sitting on many, many peices of EL84 iron |
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| icebear |
Hi
I have built the Deacaware SE84SC. I checked the spec, and tried to clone it. I bougth the parts at a local dealer here in norway (Demostenes) and rest of the parts at the huge electronic dealer Elfa. Total for me was around 600 usd. So mybe I did not save as much by cloning it??? The OPT is originaly 9.8k (I believe), but it then favoures low impedanse speakers. My speakers are quite stable at 8 ohm, so I'm using 6,8 k opt, and it should be approx. the same?? I'm running it on the Bastanis Prometheus speaker. It's a 100dB/1w dipol, and I'm not lacking any power. The sound is detailed and quite forward, but not agressive. It has a good tone. I recomend it if you have easy running speakers.
Can you believe it: One cap and one resistor in the signalpath in the amp. The speaker have a resistor in parallell and one cap in series with the tweeter. Not much :-)
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| audiousername |
Nice "Mulligan", Bjorn.
| quote: | Originally posted by icebear
Total for me was around 600 usd. So mybe I did not save as much by cloning it??? |
Your OPTs are much larger than those in the original! I'd imagine they'd have cost a fair bit. (In the original, they are small enough to fit in under the chassis at the front)
| quote: | Originally posted by icebear
Can you believe it: One cap and one resistor in the signalpath in the amp. |
That's a bit of a marketing ploy by Decware... Don't forget the OPT: it's an awful lot of curled up wire between your speakers and output valves. Anyway, if you had a direct coupled design you could get rid of that "one cap and one resistor"! |
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| icebear |
| quote: | Originally posted by audiousername
Nice "Mulligan", Bjorn.
Your OPTs are much larger than those in the original! I'd imagine they'd have cost a fair bit. (In the original, they are small enough to fit in under the chassis at the front) ] |
I know. It's made by Novarro (italian). Most likely not the best around, but ok. Cost 60 euros a pice.
| quote: |
That's a bit of a marketing ploy by Decware... Don't forget the OPT: it's an awful lot of curled up wire between your speakers and output valves. Anyway, if you had a direct coupled design you could get rid of that "one cap and one resistor"! |
Yes. I'm aware. But still, if you look into most of the amps around, it's fully packed by a lot of components. If you can say that an upgrade to black gate caps makes a difference, how aboute eliminating it? :)
I have been using an OTL before the Zen, (Trancendent T16) and I think the sound is somewhat similar. The clear grainfree and dynamic presentation. It is defenatly better than my Mullard 5-20, which got a nice tone but not as good 3D and not as clear presentation.
Bjørn |
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| audiousername |
| Sounds like you're enjoying the music. And after all that's what matters, whether you have Black Gates or not. |
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| Alex Kitic |
Usually, what we find at first is the best... although we seldom recognise it.
If you ask (me), I would say that you should bild the RH84 amp you found as an interesting choice among the first few amps mentioned... and for the moment, stick to that.
How do I know that it's any good? Well, it's my brainchild, and I also did build it and experiment with it with a whole variety of driver tubes etc.
What this design lacks is commercialization and too much modesty: I should have named it "the slayer of the Zen", and that would do for everyone...
If you need any help, just e-mail me.
Best regards to all...
Aleksandar
(tired of being modest and reading lots of mumbo-jumbo by people who did not give too much of a tought to what they are saying/writing) |
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| planet10 |
| quote: | Originally posted by Alex Kitic
If you need any help, just e-mail me. |
I'm still very much a rookie when it comes to this stuff....
What differences does the feedback between the plates do?
and
I note that the screen is not bypassed to ground?
Also, what other driver tubes did you try...
dave |
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| Brett |
| quote: | Originally posted by planet10
I'm still very much a rookie when it comes to this stuff....
What differences does the feedback between the plates do?
and
I note that the screen is not bypassed to ground?
Also, what other driver tubes did you try...
dave |
It's all explained here.
http://www.tubecad.com/march2001
and also look at Gary Pimm's site for his PP47, which cronicles the progress from a triode driver to a pentode (I only built the pentode). |
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| Alex Kitic |
The Rfb between the anode of the output tube and the anode of the driver tube makes the whole circuit behave in a different way than usual. The driver acts as a current amplifier, while the output tube acts as a current/voltage converter.
Yes, John Broskie wrote an article on the subject, concerning mainly 5965 as driver and 300B as output tube... but that is a slightly (if not completely different cup of tea). When it comes to the other mentioned design explanation, I would not know, I have to look for it on the web.
Originality? Well, it is my opinion that "hot water" was invented a long time ago, especially when it comes to electronic tubes and circuits. Still, I would say that this approach has something of its own going on... therefore I do consider it original.
There is mention of the Zen amp by Decware, and I believe I mentioned something about renaming my amp "The Slayer of Zen" in order to make it more popular. Does anyone want to know why this amp is muuuuuch better than the Zen?
Regards to all! |
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| planet10 |
| quote: | Originally posted by Alex Kitic
There is mention of the Zen amp by Decware, and I believe I mentioned something about renaming my amp "The Slayer of Zen" in order to make it more popular. Does anyone want to know why this amp is muuuuuch better than the Zen?
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yes |
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| Stixx |
Zdravo Alex,
I'd like to know that, too!
I once had a zenamp for testing, and I liked it alot. I only was worried that power would be not enough, so I am listening via a modified Leak Stereo20 now.
Ciao,
Oliver
PS Isn't Zemun a suburb of Belgrade...? |
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| Alex Kitic |
The reasons why the RH84 is far better than the Zen:
1. Driver tube
In the Zen, the driver tube is an ECC88, which by definition is not the best and most musical audio tube (OK, arguably and argumentative) -- but the main issue is the operating point for this tube. In order to function well, the ECC88 generally needs some 10mA of current, while in the Zen such conditions are not met.
The RH84, on the other hand, has an ECC81 (or any equivalent) as driver, which tube is much closer to being a true audio tube (argumentative) -- the issue being that in this case operating point requirements are met and the tube does not run a low current (for those who know what am I writing about, a bad choice of operating tube is letting it work on the low very curved part of the curve as shown in datasheets...).
2. Power
The Zen is presented as 5W per channel, which might only be P.M.P.O. like chinese cheapo speakers for PCs. In effect, it does only afford some approx. 1.5W RMS, since the tube is operated in triode mode.
On the other hand, the RH84 was designed to give 4W RMS at 1% distortion (approximately) -- and does so by operating in pentode mode. Some might immediately argue that in this case, the Zen must have a better sound since it does not operate in pentode mode or adopt NFB, but those some would be wrong, since in the RH84 the tube sounds almost identical, not to say identical in pentode mode and in triode mode (a switch might be implemented to choose from pentode to triode mode, in the latter case obviously disconnecting the resistor between the anode of the output tube and the anode of the driver tube, and obviously redirecting the connection of the g2 to the anode in order to make it "triode mode").
How is that possible? Let us skip momentarily a longer explanation and just say that there is (and should be) a huge difference between scribbling some schematic and eventually making it work, and on the other hand, doing some research and investing some time in really designing some amp...
3.
Power supply
The Zen does apply a tube rectifier to its power supply -- making it immediately sound better than if it were simple SS diodes. But, the power supply is not that sound, since chokes are not applied and the value of the capacitors and eventual smoothing resistors does not lead to a particularly low ripple on the B+. Of course, chokes are costly, are they not?! Come on...
The power supply of the RH84 is a completely different affair -- however you build it, you should stick to the guidance given on the schematics. With a tube rectifier, followed by even a simple combination like 47uF - 10H choke - 220uF, the ripple is much much lower than in the Zen, while the sound is also much improved by adopting even such a simple solution.
4.
Last but not least, of those issues that immediately get to the eye of the experienced viewer of schematics, there is a shared cathode resistor for both output tubes, meaning both output channels, in the Zen. I just cannot believe that... but that is what the schematics show, and what can be seen in pics of the interior. Well, if it is really true, we are talking about channel mixing, not channel separation: that such form of masking can lead to some mellow or interesting or whatever sound, can be immagined... but I truly do not know how to expect a soundstage from an amp that has poor separation?!
When it comes to the RH84, well, separation could be better only if the power supply was split as well and the amp built as monos... but beside that, no such design flaws (or elaborate plots to mask deficiencies caused by poor whatever wherever in the amp).
I sincerely believe that these 4 points are enough even for neophites to get a glimps of the differences between the amps in question.
Inflamatory? I do not think so. When it comes to those who like cloning amps, as they call it, just clone the RH84. For the others, who paid for their Zen and might now feel offended -- there are several simple solutions, like buying a choke and substituting a "smoothing" resistor with the choke they bought... exchanging resistors on the driver tube in order to achieve a better operating point... or stripping the nice chassis of the superfluous parts, adding a choke and remaking it as an RH84... whatever they choos, even sticking to their amp, is their own choosing now.
Regards to all -- for details of the schematic, I remind you to look for them on my site, www.tubeaudio.8m.com !
Regards to Mr. Tito, as well... Zemun rules! |
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| Alex Kitic |
Just a few words about what Zemun is, for those who would like to know...
To say that Zemun is a suburb of Belgrade, is simply derogative. Zemun is one of the several municipalities of Belgrade, and before WWII was a city on its own. In Austria-Hungary times, it was a border city of relative importance since it overlooks the Danube, just like Belgrade on the other bank. Furthermore, Zemun-polje might be a suburban area of Belgrade (and Zemun).
After WWII, Belgrade was enlarged by claiming marsh ground on the affluence of the rivers Danube and Sava. The new part of the city, quite large, is now known as New Belgrade, and has connected directly Zemun to Belgrade -- thus Zemun has become a municipality of Belgrade.
By the way, Belgrade has approx. 2 million inhabitants, which is quite large by Central-European standards.
Last but not least, Zemun "houses" quite a lot tube "gurus" and audiophiles... most certainly by coincidence -- but that does not stop me from calling it the Tube Capital of this part of the world. Some of these are quite known, like Mr. Vukusic. What distinguishes me is the fact that I am not at all commercial, meaning that my projects have never been sold or bought.
Maybe some day, when I emigrate somewhere else, there will be some "Kitic audio design", or the like of it. For now, strict hobby.
Regards to all, Alexandar |
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| Stixx |
Alexander,
since this was meant to me.....
it was not meant derogative at all. I just recalled from my several trips to Belgrade that there is one part of town called Zemun. Going from sava river on the highway to the airport or past to the border you automatically come by Zemun.
rdgs
Oliver
PS Sorry for being way off-topic!!!! |
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| Alex Kitic |
Well, either I do not know exactly how forums function, or there is some other answer to it: but, after the post about the differences between RH84 and the Zen amp, I actually expected there would be various opinions emerging...
Instead, only a reply about Zemun (it's OK, since I was not born in Zemun -- but it would not have been if I were, as they are very proud and vindicative). No one has yet said anything, neither to defend the "accused" Zen and its author, nor to contribute in any manner.
Is it that people do not review new posts on forums regularly -- or maybe after that no one has anything to say?!
Well, that would be it. Regards to all. |
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| audiousername |
| quote: | Originally posted by Alex Kitic
Is it that people do not review new posts on forums regularly -- or maybe after that no one has anything to say?! |
No. It's just that people are probably on holidays! :D
I might have some comments on the way. It's no real secret that the Zen is not a marvel of circuit design. It probably would have been a boring circuit to look at back in 1940, but that does not mean it does not perform well. |
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| planet10 |
Alex,
Your circuit certainly has me intrigued... i will build one.... it also has me thinking about a similar 6BM8 ciscuit.
dave |
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| audiousername |
| quote: | Originally posted by Alex Kitic
The Rfb between the anode of the output tube and the anode of the driver tube makes the whole circuit behave in a different way than usual. The driver acts as a current amplifier, while the output tube acts as a current/voltage converter.
Yes, John Broskie wrote an article on the subject, concerning mainly 5965 as driver and 300B as output tube... but that is a slightly (if not completely different cup of tea). |
How is it different? Do you mean it's a completely different cup of tea because you're using different valves (and pentodes v triodes)?
| quote: | Originally posted by Alex Kitic
Still, I would say that this approach has something of its own going on... therefore I do consider it original.
|
There is very little new under the sun, especially when it comes to valve circuits :) |
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| audiousername |
You wanted some comments? You got some.
I haven't heard the Zen myself, nor the RH84. I'm just commenting on what I see here. So what I say will be questionable to say the least (well no one else seems to be commenting :xeye: )
| quote: | Originally posted by Alex Kitic
The reasons why the RH84 is far better than the Zen:
1. Driver tube
In the Zen, the driver tube is an ECC88, which by definition is not the best and most musical audio tube (OK, arguably and argumentative) -- but the main issue is the operating point for this tube. In order to function well, the ECC88 generally needs some 10mA of current, while in the Zen such conditions are not met.
The RH84, on the other hand, has an ECC81 (or any equivalent) as driver, which tube is much closer to being a true audio tube (argumentative) -- the issue being that in this case operating point requirements are met and the tube does not run a low current (for those who know what am I writing about, a bad choice of operating tube is letting it work on the low very curved part of the curve as shown in datasheets...) |
Low current in input/driver valves is sadly something done rather often, perhaps out of ignorance, but I suspect because of power supply requirements. Yet, by allowing the input/driver triode to stray into the murky botton of the curves, the distortion produced may cancel with some of that produced by the output stage. (Of course, I don't know if the Zen was designed this way)
| quote: | 2. Power
The Zen is presented as 5W per channel, which might only be P.M.P.O. like chinese cheapo speakers for PCs. In effect, it does only afford some approx. 1.5W RMS, since the tube is operated in triode mode.
On the other hand, the RH84 was designed to give 4W RMS at 1% distortion (approximately) -- and does so by operating in pentode mode. Some might immediately argue that in this case, the Zen must have a better sound since it does not operate in pentode mode or adopt NFB, but those some would be wrong, since in the RH84 the tube sounds almost identical, not to say identical in pentode mode and in triode mode (a switch might be implemented to choose from pentode to triode mode, in the latter case obviously disconnecting the resistor between the anode of the output tube and the anode of the driver tube, and obviously redirecting the connection of the g2 to the anode in order to make it "triode mode").
How is that possible? Let us skip momentarily a longer explanation and just say that there is (and should be) a huge difference between scribbling some schematic and eventually making it work, and on the other hand, doing some research and investing some time in really designing some amp... |
This is my main gripe with the Zen. Claiming that the power output is almost 3 times its actual power output is misleading. You can argue that the difference between 1.8 and 5 watts is not so important as other characteristics of an amplifier (especially is the buyer has efficient speakers), but In fact there is an article trying to justify the embellished power output specification on the site somewhere. (To be fair, it was never stated that 5W was continuous rated power, and somewhere else on the site it states that the 'real' power rating is 1.8W)
Saying that "in the RH84 the tube sounds almost identical" is very subjective. The ear may not be easily fooled but the mind is :( I'd expect at least some to say that two RH84s sound different if you told them one was triode-strapped (when it wasn't). Anyway, pentode mode need not be necessarily inferior to triode mode, it's just a different set of comporomises that have to be made. And it seems that you've managed the problems (high output impedance and higher distortion than triodes) with the local feedback around the output stage.
| quote: | 3.Power supply
The Zen does apply a tube rectifier to its power supply -- making it immediately sound better than if it were simple SS diodes. But, the power supply is not that sound, since chokes are not applied and the value of the capacitors and eventual smoothing resistors does not lead to a particularly low ripple on the B+. Of course, chokes are costly, are they not?! Come on...
The power supply of the RH84 is a completely different affair -- however you build it, you should stick to the guidance given on the schematics. With a tube rectifier, followed by even a simple combination like 47uF - 10H choke - 220uF, the ripple is much much lower than in the Zen, while the sound is also much improved by adopting even such a simple solution. |
What can I say, chokes are heavy and expensive!
| quote: | 4.Last but not least, of those issues that immediately get to the eye of the experienced viewer of schematics, there is a shared cathode resistor for both output tubes, meaning both output channels, in the Zen. I just cannot believe that... but that is what the schematics show, and what can be seen in pics of the interior. Well, if it is really true, we are talking about channel mixing, not channel separation: that such form of masking can lead to some mellow or interesting or whatever sound, can be immagined... but I truly do not know how to expect a soundstage from an amp that has poor separation?!
When it comes to the RH84, well, separation could be better only if the power supply was split as well and the amp built as monos... but beside that, no such design flaws (or elaborate plots to mask deficiencies caused by poor whatever wherever in the amp). |
A shared cathode resistor has been done in other amps too, notably Bob Danielak's original Darling. Yes, they may cause channel mixing to some degree, but it shouldn't be too great as long as the resistor is adequately bypassed (i.e. the cathodes of both output valves are at a point which sufficiently mimics AC ground). I can't say whether the shared cathode resistor compresses, or indeed expands the stereo image (I haven't got an SE amp with that 'weird' arrangement).
| quote: | | I sincerely believe that these 4 points are enough even for neophites to get a glimps of the differences between the amps in question. |
Differences: Choke-filtered power supply in RH84, Pentode mode operation in RH84, different input/driver valve, individual bypassed cathode resistors.... um....
| quote: | | Inflamatory? I do not think so. When it comes to those who like cloning amps, as they call it, just clone the RH84. For the others, who paid for their Zen and might now feel offended -- there are several simple solutions, like buying a choke and substituting a "smoothing" resistor with the choke they bought... exchanging resistors on the driver tube in order to achieve a better operating point... or stripping the nice chassis of the superfluous parts, adding a choke and remaking it as an RH84... whatever they choos, even sticking to their amp, is their own choosing now. |
It's clear that you feel the RH84 is FAR superior to the Zen for several reasons, like increased power output, lower distortion? etc. But remember, that was the promise of solid state! The RH84 is probably the more complex design, and may very well measure better on paper, yet that doesn't mean that everyone will like it more (some may just like an anemic, distorted sound, who knows?)
Anyway, I hope I haven't offended you, and thanks for sharing the design and taking time to explain why you believe it's better than the Zen (I can't say whether I agree, I haven't heard either :bawling: ) At the very least the RH84 is something a little different from lots of other boring designs out there, and that is refreshing. (Of course not saying that boring designs can't perform well ;) )
Maybe some comments from some people who have actually heard both designs? Or maybe there aren't any such people around :(
Merry Chistmas to all
Edit: some formatting mistakes |
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| Alex Kitic |
For the moment, just a quick anwer to the only question that might look as urgent: the issue on whether there are "that many people who have heard any of the designs".
First of all, this is the first time I had approached any forum in all these years both as a "searcher" and "websiter" (name for a person who has a website of his own?). Partly because some of John Broskie's sarcasm when it comes to forums and posting has obviously gotten to me -- but also because usually a person with a certain level of knowledge and experience cannot find anything new reviewing posts on forums, no pun intended, since it is quite obvious that the forums are mainly "attended" by people with little experience and/or knowledge. No pun intended, again.
Now the answer -- yes, quite a lot of people have built some of the RH amps for themselves, the LAF version of preamps was built in a good number of clones "all over the world". To most people, my designs have been both a pleasure to listen, and an eye-opener of the sort.
But, I sincerely believe that none of these people is participating in this forum, so unless I i.e. email a link to some of them, I don't think anyone will know that it is the moment to "stand up and say".
And, for that matter, it is not. I regard this question as a little indiscretion of the sort - not offending (as I am not offended by those who distrust) but uncomfortable (like "when I do not know what else to say, I will say it"). Of course, I will not email links to this forum to friends so they can "defend me" -- I am quite capable of defending my ideas on my own.
As soon as I find the time, I will make another post about the other, technically more important issues than this purely personal that I just had to reply to before too many people see it :) The technical issues mainly regard the fact that we cannot simplify things to triode vs. pentode, especially if we take into account known facts that have created a bad reputation for pentodes. On the other hand, I do not believe that people like to listen to "poor" sounding equipment -- just that once they have invested in this equipment, they are too vain to recognize the fact that what they own is simply not good (enough).
Regards,
Aleksandar |
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| audiousername |
Forums can be strange places sometimes. I'm sometimes inclined to agree with the sarcasm from people like John Broskie and Geoff Moss.....
| quote: | Originally posted by Alex Kitic
But, I sincerely believe that none of these people is participating in this forum, so unless I i.e. email a link to some of them, I don't think anyone will know that it is the moment to "stand up and say".
And, for that matter, it is not. I regard this question as a little indiscretion of the sort - not offending (as I am not offended by those who distrust) but uncomfortable (like "when I do not know what else to say, I will say it"). Of course, I will not email links to this forum to friends so they can "defend me" -- I am quite capable of defending my ideas on my own. |
Oh dear, I was trying to tread lightly! The intention of my second post was to elicit some discussion about the RH84, and maybe make the design better known to DIYers (at least those who frequent this forum)
When I said| quote: | | Maybe some comments from some people who have actually heard both designs? Or maybe there aren't any such people around :( |
I was expressing regret that I didn't belive there would be many people out there who had both amplifiers. Until reading this thread I had not seen the RH84, and thought it might me a new (or relatively unknown) design. I don't mean to attack or offend :)
Actually, I'm wondering why you said that the RH84 may be "a completely different cup of tea" to the John Broskie article. I admit I'm no master when it comes to circuit design, and was looking for an explanation to see what I've missed.
| quote: | | we cannot simplify things to triode vs. pentode, especially if we take into account known facts that have created a bad reputation for pentodes. |
Agreed. There is no reason why pentodes must sound bad!
| quote: | On the other hand, I do not believe that people like to listen to "poor" sounding equipment -- just that once they have invested in this equipment, they are too vain to recognize the fact that what they own is simply not good (enough).
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:D That's true too |
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| fdegrove |
Hi,
Hello Alex,
Good to see you're discussing one of your amps here...
Regarding posting on a forum, Mr. Broskie may have had bad experiences with them in the past, I don't know, but don't let that stop you from sharing and helping others through their paces.
After all, it's not because we had to learn with our noses stuck in books and a soldering gun ready that everyone else has to as well.
Anyway, expect people to be skeptical. People always are.
The difference is, here they'll dare to tell you whereas they probably won't if they'd be standing next to you. (I know you're almost 7 foot tall...Kidding.)
BTW, the plate to plate feedback...Isn't that positive FB that's being applied. I only had a quick glance so I could be wrong.
Thanks for sharing your work with me, btw. I'll take a closer look ASAP.
Cheers, ;) |
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| audiousername |
| quote: | Originally posted by fdegrove
BTW, the plate to plate feedback...Isn't that positive FB that's being applied. I only had a quick glance so I could be wrong. |
Frank, just to save some time :) , the feedback is negative, because the plate of the input/driver is at the same point as the grid of the output valve, and hence has the opposite phase to that of the plate of the output. Plate of output to grid of the input/driver would be positive (in a 2-stage design). Some more detail about (what I think Alex's output stage is functioning as) here
Alex, I think I forgot to say this before, but thanks for sharing! It's always nice to see some new application of ideas. :D |
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| Yugo |
Aleksandre,
during the development of your RH84 did your try to combine the output pentode in UL mode and to compare the results!?
You will also get a little NFB through UL tap! I am asking you this because I sometimes prefer to listen the UL tap than the triode or pentode mode on my PP 6CA7 amp(output T/X is purchased from Maplin),depending of what kind of music I am listening to! There are SE output T/X at the market with UL tap at 43% windings,IIRC. They are little more expensive than the ordinary SE but I think they are worth to try.
Regards,
Yugovitz |
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| Alex Kitic |
First of all, let me apologise if my previous comment was a
little hasty -- maybe I have overreacted, but when it comes
to that, I might be a little touchy. On one hand, I live
where I live and my life in the last 15 years has not been
milk and honey, in a sense that most western democracies'
citizens cannot quite imagine. On the other, it is a sad
truth that "no one is a messiah in his own village" -- far
from the notion that I would want to be considered a
messiah or guru!
Let me comment the other, more important issues here. The
last, but very crucial question, came from Yugo. No, I did
not try it in UL mode, and aside the fact that I have no UL
tapped transformers at hand, it would not serve any
particular purpose. Because, as I see it, we are not
talking here about pentodes/tetrodes and the way to use
them, but about a quite different circuit topology which
actually exploits what a pentode can give us, where the
pentode itself is not to be viewed as a pentode, but as a
tube of "such and such charactheristics".
The concept of using a pentode as a current/voltage
converter has been explained in the already linked John
Broskie article. But, why I say that the circuit is a
different pair of shoes can be seen by reviewing the pages
a little more carefully, and paying particular attention
after page 8. The problem with reading those articles is
the fact that they were split as html pages in a not so
orderly manner, and quite long to read -- you had to print
them to read them carefully. Most probably that is why the
author started converting his new articles in .pdf files.
Until page 8, all notions are very general, to say the
least. In fact, you could use them as ideas to develop your
own concepts, but most readers do not have enough knowledge
or immagination to venture on such a journey. From page 8,
a more direct approach begins, with a 300B tube and a
driver to be chosen (in the end, it is a 5965). And, this
circuit which is proposed, while being quite interesting,
especially for further refinements, has little to do with
the RH series of amps, except for the fact that they do
resemble in the manner the tubes are used. A similar issue
is obvious when we speak about Loftin-White amps: they come
in two flavours -- one (which I maybe wrongly consider to
be the "true" one) is when the current draw of the driver
thru the anode resistor is directly used to bias the output
tube, since the driver is beneath the tube itself; the
other is when the driver directly biases the output tube,
but is not restrained to working beneath the output tube,
but gets it's HT from the B+ rail, thus allowing it higher
voltage swings.
Now that we mention the famous "Darling" amps, I recall
there is a Loftin-White variety of Darling, which is just
like the second type I mentioned. And, just like these two
topologies actually have in common only the fact that the
driver is directly coupled to the output tube, my RH amps
and the amp described by John Broskie have little in
common.
To make a digression, the Darling amps somehow came to be
famous -- and I never understood why. Aside the fact that
the available power in one SE tube mode is quite lowish,
maybe the 1626 is a very common tube on the American
continent... but in Europe, you would better look for a 10Y
since it is easier to find. And, I would not compare the
two neither as price nor as charisma.
Now to the point of my reaction -- simplification of
concepts. Maybe it is that you i.e. need some knowledge to
be able to see all aspects of a design, and that is why
people do not immediately see those differences -- which I
can understand when it is about nuances.
1.Choke-filtered power supply in RH84
This is a huge difference, you know?! Not that it is or
should be original, but it is "the most sound way" to deal
with an SE amp power supply. The fact that chokes cost more
than sand resistors is not to be condoned here, since
no-one said it had to be a 100H/100mA choke wound with
silver and gold threads, costing xy thousand US$! A quite
simple and cheap choke would do a great deal of good to the
design, yet it was ommitted for more than obvious
cost/profit reasons.
2.Pentode mode operation in RH84
As I already said, pentode mode operation is not the true
definition here. And, if said with that formulation, it
immediately implies a lesser design. On the other hand, we
are talking about the same tube used in the Zen amp...
using it in triode mode still leaves us with a pentode,
since aside the fact that between the grid and anode you
still get two grids, you cannot alleviate the fact that the
electrons do not get to g2, g3 and a in a different
fraction of time -- since g3 remains at the potential of
the cathode (it does not have a separate pin -- and
furthermore, the opion of using the pin which as I recall
exists on the SV83 is not used in the Zen!).
On the other hand, pentode mode means more power, where the
PMPO chepo rating of the Zen becomes a more realistic
figure, making it quite useful for ordinary people with
ordinary 86dB/W/m speakers.
Finally, when I said "almost identical sound" I said that
on purpose, but in marketing terms I should have said
"identical". Because, I will not fool myself that there is
not difference in sound, both because I can hear it on my
equipment with my ears, and since theoretically there
should be some difference. But, the difference is so slight
that we can call it "almost identical" -- to tell the
truth, it has more power and more attack and better
definition (to all who have listened to it) in the "pentode
mode" or "RH mode" as would be more appropriate.
3.different input/driver valve
Actually, although I stressed the difference between
valves, the issue here is more like "incorrect operating
point vs. correct operating point". If we just correct the
operating point in the Zen amp, it WILL sound much better.
The reason why an incorrect operating point is employed,
and why a second even worse is offered to the user, remains
unclear. The current to be consumed is most certainly not
an issue here, since the power transformer and the
rectifier are more than capable of supplying it... and the
filtering caps are not that small not to be able to give an
adequate ripple characterstic to the B+ supply with
increased current. I will not fall in the trap of making
conclusions by myself, although, like with the PMPO rating,
I would expect the author to write an essay on "how
specially selected tubes by especially knowledgeable people
can give discerning sound qualities to the illuminati"
(oops, I did it too: that was sarcasm, but at least it does
not give anyone a liable case).
4.individual bypassed cathode resistors
Well, since we are talking about stereo, not dual-mono... I
consider that a "sine qua non" condition. Darling or no
darling, it is both logical and straight-forward. And, it
is usually done with sand resistors, so it costs so little
one must not mind. The fact that in the Zen a special
resistor with cooler is used does not do the trick of
making me believe that it is about the price of components.
When it comes to the point of mimicking AC ground, I would
at least bypass. If you have a cathode biased SE amp at
hand, try removing the bypass caps from the output tube's
cathode resistors, and then see for yourself whether the
amp still has the same gain: if it has, then I am wrong...
if it has not, then you are wrong in assuming that the case
of mimicking AC ground can be applied to this instance. On
the other hand, bypassing the "common cathode resistor"
might prove useful.
As you can see for yourselves from this lengthy "essay",
the differences are not subtle at all -- and while to those
who have not noticed by themselves what I have just written
the previous short-definition of differences might sound
correct, I hope that once they read this further
explanation it will become if not obvious, then at least
"more interesting, as something to think about next time".
Regards to all, and Merry Christmas!
Aleksandar |
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| audiousername |
| quote: | Originally posted by Alex Kitic
First of all, let me apologise if my previous comment was a
little hasty -- maybe I have overreacted, but when it comes
to that, I might be a little touchy. On one hand, I live
where I live and my life in the last 15 years has not been
milk and honey, in a sense that most western democracies'
citizens cannot quite imagine. On the other, it is a sad
truth that "no one is a messiah in his own village" -- far
from the notion that I would want to be considered a
messiah or guru! |
That's ok. No offence taken :)
| quote: | Originally posted by Alex Kitic
But, why I say that the circuit is a
different pair of shoes can be seen by reviewing the pages
a little more carefully. |
I see what you mean now. Thanks for the explanation.
| quote: | Originally posted by Alex Kitic
To make a digression, the Darling amps somehow came to be
famous -- and I never understood why. |
Same thing here. Not particularly cheap (but nowhere as expensive as 10Y). I think you can get them for something like 10 for US$29 from Fair Radio or something (haven't checked in a while), so that's probably why they're popular. Rather non-linear valves too... and as you've said, a paltry amount of output power... but that's an argument for another day.
| quote: | Originally posted by Alex Kitic
Now to the point of my reaction -- simplification of
concepts. Maybe it is that you i.e. need some knowledge to
be able to see all aspects of a design, and that is why
people do not immediately see those differences -- which I
can understand when it is about nuances. |
I see the differences clearly. I was listing some of them to hopefully open some discussion about your amplifier design. In any case, your explanation of the differences will be most informative to any who wish to build the RH84 (or Zen) and see the differences, and the reasons for which they are different. It's nice to see someone spending the time to make things clear :)
| quote: | Originally posted by Alex Kitic
4.individual bypassed cathode resistors. |
Sorry, I thought the cathode resistors were bypassed on the Zen (I should have checked the facts before I opened my mouth :whazzat: )
Of course the gain will drop with the cathode resistors unbypassed, if it didn't, quite a few textbooks would have to be rewritten (and perhaps a few laws of physics). Hmm.... the Zen is a stranger design than I thought... purposely making a circuit to allow channel mixing :confused:
| quote: | Originally posted by Alex Kitic
Regards to all, and Merry Christmas! |
Merry Christmas and a Happy New Year to you too. :) |
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| G |
I built a revised version of the little Zen amp using a 5687 as the input tube. It was a very nice sounding and involving amp. I feel the EL84 is the best Pentode or tetrode to use in triode mode soundwise but you are limited in the voltage swing you can apply to the grid ( unless you exceed its maximum rated plate voltage) and it will clip during a powerful passage because of the limited grid bias voltage headroom available without frying the tube. They sound wonderful for light Jazz and female vocalist. There are a couple of Diana Krall songs with such over emphasized mids and mid highs that they will cause the little guys (the EL84s) to clip unless you are listening at a lower than desirable level. Of course there's no pint in listening at that point. While it's sound is more articulate and airy it's bias voltage and power limitations make the EL34 a far better tube for a good solid all around tube amp. Anyway, the schematic for the sweet little EL84 SE amp (my first and arguably most enjoyable amp with the right music) is posted below. If you build it, enjoy.
G |
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| G |
| Here is the schematic for the power supply as I built it. |
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| Alex Kitic |
Hi, Gavin...
Nice little elaboration of the Zen-amp. Nice little power supply. I do not have the time at the moment to review the operating point of your driver, although it does seem to me that it is drawing very little current.
Did you actually take a peak at the site previously mentioned and read the last few pages of the thread? Nice as your amp is, the whole post looks to me like an anti-climax. After some discussion on design principles, you just cool us off with nice-little-Zen-revisited and a story about EL84 vs. EL34.
Did you consider that the EL84 can overcome those subtle deficiencies you mention just by being operated differently than in triode mode (1.8W max) -- for instance, in RH mode ? :)
Regards,
Aleksandar |
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| G |
| Actually all I meant to add tto the thread was that the linearity and output impedance of the input stage makes a pronounced impact on the overall sound of the amp regardless of the topology of the power stage. I have not read far enough into the thread to appreciate the differences between a good old SE triode mode and RH mode. When I have the time to give it a thorough read I will. I was just putting out a design that while simple is probably the best sounding amp i have heard (subjectively speaking of course) except for a Parafeed 300B amp I heard through a pair of very efficient Altec horn loaded loudspeakers in a well treated very acoustically nuetral room. That sound and level of enjoyment has been a personal benchmark for me. I'm certainly not the most learned member in this forum and I am certainly not qualified to argue the virtues and shortcomings of one topology versus another. AC analysis except on the most basic level is not my cup of tea. I suppose that if I was dissatisfied with the sound of a Pseudo triode single ended output stage then I would be more versed in design theory and more qualified to have an opinion one way or another. I am very satified and content with the sound of SE amps in triode mode but dislike the sound of Class A in pentode mode and have not felt the need to experiment with ultralinear mode as I don't think the result will be worth the sacrifice of my very limited free time. I just enjoy listening in ignorant bliss. I put my version of a SE EL84 amp out as a easy to build, inexpensive rewarding option for a project. |
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| Alex Kitic |
Gavin (mostly),
sorry if you feel offended -- but sometimes you should read a thread (just like sometimes I need to...) before you post.
Since the thread was named EL84SE design recommendations, and my name was mentioned, I felt the urge to see what was it all about... and, there we were again, with old fashioned, maybe it would be better to say market fashioned -- pseudo triode amps.
Not that pseudo triode does not have it's merits -- it's the easiest way to use a pentode/tetrode tube in any amp. BUT what I am trying to do is convice everyone to try to let go of old stereotypes and try something different, if not new.
When I was thinking that at least in this thread we were finished with the market-minded simple Zen amp (and what a name, at that), here you come with "Zen revisited". I did not do any calculus on your driver's operating point... and there is no need for that. Just review the last few pages of posts carefully, maybe read some of the linked articles and review the linked sites.
Regards,
Aleksandar |
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| G |
| Alex I don't think you owe me an apology but some might frown on the fact that you have taken someone else's thread and used it as your personal soap box. What type of "sound " pleases each of us is different and for the most part has nothing to do with complexity or technical excellence. It is a subjective opinion in which logic does not play the lead role. You can expound on the virtues of a design but don't expect everyone to take your opinion as fact or to agree with you. I was offering a SE EL84 design to the originator of the thread which is what he wanted in the first place. I look at DIY electronics as productive and enjoyable way to spend some of my free time. I think you might be looking for more than that and I wish you luck. I fear though that you may be dissapointed when reality doesn't quite meet your expectations. |
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| planet10 |
The more designs the better... Alex, your design is very interesting, and i'll certainly get around to building it... but i will also build some Mulligan inspired versions too. The ECC81 up front seems a bit pedestrian (i do have some nice ones, but even more ECC85s). Have you tried any other input tubes?
dave |
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| Alex Kitic |
Well, now it seems that I have stolen the thread. I still do not think so. The thread is about EL84SE design recommendations -- and I think since I was mentioned in the first place, and secondly offered my design to whoever wants it, it is quite natural that I should now stick to it, both defending my design and trying to prove that it is the best available :) There is nothing bad about it, I think.
| quote: | | I think you might be looking for more than that and I wish you luck. I fear though that you may be dissapointed when reality doesn't quite meet your expectations. |
I do not know what to think of that. Yes, it is true that I am looking for more than that -- let us call it exploring and experimenting, only maybe on a more technically advanced level than might be customary in contemporary DIY circles.
When it comes to the part of being dissapointed, well I am not at all dissapointed with what I got so far with my designs -- on the other hand, I tend to be dissapointed with most people... some will negate obvious things (for a whole variety of reasons) while others might be reluctand to try the offered solution, maybe out of not understanding what it implies, or just because of the fact that they have already made up their mind about things (or their mind has been made up for them). But that goes way beyond DIY audio, it's mostly been like that all my life.
Let us get back to constructive issues... planet10 and different valves at the input/driver position.
Of course, the configuration can be designed for a different input tube, involving a different calculus of operating point and resistor values etc. I presume you asked about whether some other tubes might be inserted in the socket and tried "right out" -- and of course (were would else the experimenting be) they were.
ECC83/12AX7 types can be inserted in the driver socket, and drive the power tube to full power -- the operating point will be correct, although a little unusual, with low voltage across the tube and quite a lot of current (ECC83s are usually applied more voltage and much less current) -- but correct after all and not harmful to the tube. Good sound, somewhat mellower, might be a better "tweaking solution" to some.
5965 and E180CC are a second solution that works, maybe even better than the ECC81/12AT7. The transconductance of the tube is higher, so it makes up for the loss of amplification factor, and the amp is obviously driven to full power. Very good sound, maybe even better than the tube it was designed for (although a little "faster" than some might like).
ECC82/12AU7 and xSN7 types cannot be used "directly" (of course, the octal types will need another socket to be fitted), because their amplification factor is not high enough, therefore the amp is never driven to full power. The sound? Nothing special.
6SL7 and similia cannot be used either -- the amplification factor would be high enough, but the transconductance is too low to make it work, and they just cannot drive the output tube to full power.
Does this improve anything? Well, those who try it can speak for themselves, and give opinions...
| quote: | | The ECC81 up front seems a bit pedestrian |
Well, maybe that is the problem with this design... the ECCxx series seems a bit pedestrian! If it were octal tubes, maybe it would attract more interest? If you ask me, there is hardly any tube more "pedestrian" than EL84 -- but I still like it.
The amp was not meant to be expensive or exotic -- yet to perform and sound very well, even with normal speakers. Something of an eye opener for people who think only amps with 300Bs and similia are worth building and listening to!
If the story is about pedestrian tubes... well, why the thread then? I am working (actually waiting for inspiration and time) to do some work on a less pedestrian RH amp, with 307A/VT225 tubes. Directly Heated Pentode in RH mode... less pedestrian, ha? Eventually, some exotic driver? But that would be abusing the thread, wouldn't it?
Let me know...
Aleksandar |
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| slowmotion |
| quote: | Originally posted by Alex Kitic
I am working (actually waiting for inspiration and time) to do some work on a less pedestrian RH amp, with 307A/VT225 tubes. Directly Heated Pentode in RH mode...
Aleksandar |
Sounds interesting.........
cheers |
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| Alex Kitic |
Hey, guys, is it possible? The moment I say VTxxx someone is interested!!!
Well, in a spirit of cooperation, and since I owe this amp anyway to quite a lot of people who cared to supply me with datasheets (at the time, not available on tdsl), even with tubes... I am inclined to sharing ideas on this.
I only think that for this topic another thread should be created. Who is going to indulge on that? I think I've been maybe too prominent during the last few days, so I might attract some negative toughts... :(
So, create a thread (i.e. generic, like "307A SE amp recommandations...), and I will join!
Regards,
Aleksandar |
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| audiousername |
| quote: | Originally posted by Alex Kitic
The thread is about EL84SE design recommendations -- and I think since I was mentioned in the first place, and secondly offered my design to whoever wants it, it is quite natural that I should now stick to it, both defending my design and trying to prove that it is the best available :) There is nothing bad about it, I think. |
There is no need to defend your design. No one is attacking it, just looking at it and asking questions. There is a difference.
| quote: | Originally posted by Alex Kitic
If the story is about pedestrian tubes... well, why the thread then? I am working (actually waiting for inspiration and time) to do some work on a less pedestrian RH amp, with 307A/VT225 tubes. Directly Heated Pentode in RH mode... less pedestrian, ha? Eventually, some exotic driver? But that would be abusing the thread, wouldn't it? |
You said yourself somewhere that the output stage in "RH" mode is run as an I/V convertor. As such, a pentode input stage (and its inherently high Zout) may improve performance. At the very least, it will give a different sound. Of course, pentodes are less linear and all of that.... The high Zout shouldn't mess up the HF performance too much anyway since Rfb shunts the milleramplified Cgp of the output valve, which creates a HF pole, hence limiting response. (I admit this is arguable, the grid of a pentode presents an inherently low capacitance - in comparison with triodes.)
To those wanting Alex to use "Less pedestrian tubes" The EL84 and ECC81 are boring, I admit. That doesn't mean that they are poor performers, though. (Said by someone who rarely uses "pedestrian tubes" himself)
Alex, to get more people interested, why not try something like "RH mode" 813? That'll get people interested with its glowing filament! Or if you're not going to build a 1kV+ power supply, try something with KTxx valves. They tend to get people excited (look at all the new types given a KT designation, KT90, KT100 etc). If you're not looking to spend too much money, the KT33/KT33C is cheap. No one seems to want them. |
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| Alex Kitic |
A relatively short answer, for starters...
1) Defending my design
This is an obviously bad choice of words (command of the english language or not, I still speak some other language at home :) ). I should have said ADVOCATING -- does that sound better?
2) Pedestrian tubes
I agree that people should not regard ANY tube as plain pedestrian (OK, xCL86 xCL82 and similia might truly be pedestrian tubes... but that does not make tham uninteresting, since people have differing needs, possibilities and get satisfaction from building i.e. small amplifiers in the physical sense of the word).
On the other hand, those not interested in pedestrian tubes should immediately skip a forum on EL84 design... and go for some 300B alternatives, as I belive there are some. But, what is worth and feasible for an EL84, can be applied generally to any tetrode/pentode tube of higher interest, like KT90 or 6550... whatever.
3) RH mode 813 and similia
Well, when it comes to 813, we get to another set of cards. This tube can deliver very very much on its own, "without help of any RH concoction" -- just wire it in triode mode, and you will immediately get the goods, like high power output etc. But this is what I like to call "an EHV tube" -- extremely high voltage tube, where by extremely high voltage I assume everything a garden variety instrument cannot measure directly (like 700V DC). Most sites tend to stress the issue of danger, and I regard it as a necessity -- but at EHV levels (EHV in terms of audio applications, of course), I think that i.e. 1000V DC is dangerous to most.
4) What tubes need it?
I did some RH circuitry simulations for KT90 -- a long time ago, and I will try to find the files since I've recently been given some 6550's (the good variety, ST shaped, without holes in the anodes) and would like to try it, especially since at the time I called it "second generation RH". The same is true of i.e. 300B -- application of the same "second generation RH" circuitry did give some extremely interesting results when simulating. But the results I am talking about are numbers, like 9W with 1% distortion, as compared to the usual 9W 5% distortion advertised for 300B SE circuitry. How would it sound with triodes? Is it truly needed? You can easily get 6W of power from a KT90/6550/KT88 in triode mode, thus surpassing the 5W limit I believe to be
"the real world goal" for volksamplifiers in the sense that most people will find the power level to their listening satisfaction with ordinary "mid efficiency speakers" found in most homes.
What I want to say is that generally, I was never interested in simulating circuits (and designing them -- as some people here find to be un ugly and offensive term) if I did not have the tube at hand. Cost was never an issue for that, since I rarely paid "internet prices" for any tube I've stashed in my "collection").
Application of "RH circuitry" (if I am allowed to call it that) to whatever tube might be possible -- but just like the previously in this thread mentioned "promise of solid state", sometimes it might not make sense. The sound of a tetrode/pentode is more than obviously inferior to the sound of a triode -- if used conventionally.
During time, several application strategies were developped for tetrode/pentode tubes to bridge the gap between higher efficiency and inferior sound, like ultra-linear taps. Consider my "circuitry" as one such approach -- and it does deliver the goods, in the sense that the sound is much improved, as I previously said "almost identical to the triode connected tube in the same circuit". And almost identical can also mean "better". But it does need to have a reason for applying. A 300B with same power and less distortion (I did not try that one as for sound) does not necessarily mean "better than the usual" (just like the promise of solid state) -- on the other hand, 4-5W with less distortion and better sound compared with 1.5W with more distortion and lesser sound (from an EL84) seems to me a legitimate goal.
5) Pentode drivers
Yes, in theory a pentode driver might "do the trick" even better, since it has higher output impedance than triodes. With current sources, a high output impedance is very welcome (unless I got that wrong, and I sincerely believe I did not). The only reason why I did not try that one is given by the fact that a) the triodes mentioned above, which are mostly "garden variety" pedestrian types (easy for everyone to get hold) do the job quite well;
b) my "collection of suitable pentode drivers" is very low; c) exchanging the driver ECC81 i.e. garden variety type with some "better sounding NOS tube of the same or similar type" does give rewards in terms of better sound (i.e. Ei ECC81 vs. Telefunken ECC81, or Philips 6201, or "you-name-it-highly-regarded-NOS") -- that might implicate that "sonically inferior pentode tubes" might actually give lesser results in the particular application -- and their contribution in efficiency terms is not necessary for the task.
Finally, one issue should be considered, which most of those who tend to dismiss others with punctuation marks obviously overlook in their might -- whatever you want to do, takes time and effort. In order to design a circuit (i.e. 307A RH mode) I need to have spice models at hand. If I do not (and in 90% of the cases such models are not readily available) I have to "write" the model on my own, which is not that difficult as it looks, but takes some time and effort. Once the model is ready and inserted in the circuit, there is more work, thinking, and knowledge to be applied, in order to get some result. Therefore, the "collection" of RH circuits is relatively limited -- I did only what was interesting to me, or requested by friends -- and of course, when I had the time to do it.
Regards to all,
Aleksandar |
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| Andrewbee |
Hello Aleksandar,
Thank you for your interesting posts and please keep them coming. You seem to think differently to many people with regard to circuits / tubes. I will be trying the RH84 within the next week if I can find the parts in the junk box which I should be able to.
I have questions for you though. What are your thoughts on fixed bias in this circuit? Is it a waste of time? Did you try it?
I have sets of EL84's and also 5V6's and while I will build it initially with EL84's I also plan on trying the 5V6's.
Thanks
Andrew |
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| G |
| quote: | Originally posted by Alex Kitic
Hi, Gavin...
Nice little elaboration of the Zen-amp. Nice little power supply. I do not have the time at the moment to review the operating point of your driver, although it does seem to me that it is drawing very little current. |
That would depend on your definition of very little. The current through the driver is around 10-12 mA.
| quote: | | Did you actually take a peak at the site previously mentioned and read the last few pages of the thread? Nice as your amp is, the whole post looks to me like an anti-climax. After some discussion on design principles, you just cool us off with nice-little-Zen-revisited and a story about EL84 vs. EL34. |
After having read the rest of the thread, as you suggested, I can see you are coming from.
| quote: | | Did you consider that the EL84 can overcome those subtle deficiencies you mention just by being operated differently than in triode mode (1.8W max) -- for instance, in RH mode ? :) |
I would indeed wouldn't it? How about a older yet still available tube like the 807. I was going to build a SE 807 amp but did not when I realized how little rms power I was going to get out of the circuit. Perhaps you can explain how the feedback resistor is calculated for a given input/output tube combination? Also I suspect that using a UL connection to the output tube in a "RH mode" amp would make the sound of the circuit differ from that of a pentode connection as was previously suggested in this thread. |
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| Alex Kitic |
Gavin:
To start with the current drawn thru 5687, as I said, I was not going to do any calculus on that -- if not directly understood, I was actually sorry for being too dismissive. If it is 10-12mA, which seems quite a good operating point for the 5687, than there is no question whether it does sound a lot better than the original Zen.
807 -- although not quite the same topic (the thread is about EL84) -- you must have seen the RH807 amp on my site. This one was indeed built in a variety of versions, including an "integrated" one. And, as on the published schematics, it has quite "enough" power -- if some 5W as compared to the meagre amount in triode mode would be enough for you.
Furthermore, the 807 topic can be extended by either increasing the B+ (no changes in the circuit needed) just taking care about the Rk of the output tube, and the R before g2, in order not to surpass anode dissipation and g2 voltage ratings -- and it will give even more power. Alternatively, exchanging the 807 for a little more powerful members of the same family, like 6L6 specials, or 7027A, you can get up to almost 10W.
The calculation of the resistor seems to be 1:5 approximately, meaning that the Rfb is actually up to 5x larger than the Ra of the driver tube... it's a mix of current from the B+ rail, and current from above the anode of the output tube (and indeed some feedback) that does the trick. Actually, once that basics are established, there is a lot of trials by simulation and some thinking to be done. Not being a scientist, I have never given it a serious tought to make some exact rules on calculus.
UL taps would obviously do something with the sound -- as I said, I did not try that one, among other reasons because I did not and do not have at hand transformers with UL taps. It might improve the sound -- and it might decrease the power, as well? In order to give a serious answer that would not cause eventual ridicule, I must think a little more about it. It did not matter to me, in principle -- so I never dismissed that idea completely, nor gave it any particular consideration.
Andrewbee:
Great! Finally someone is going to give it a try (I mean, counting the people who were reading about it lately in the forum)! Just go ahead, and if you have any questions or problems, just send me an e-mail.
About fixed bias -- well, I think that would not work, you know... it is important for the circuit to have a Rk below the output tube -- just as it is important for the Rk of the driver tube not to be bypassed by a cap. Both cases invalidate the previous results in simulation tests. Theoretical reasons -- well, I would have to take another look in various texts (and try to recollect the toughts I had while working on the RH circuit).
6V6 (5V6 is a 6V6 with different filament requirements, or am I wrong?) -- the results would be similar. I think the same schematics for the RH84 can be applied to 6V6, since those tubes are quite similar (anode dissipation, etc.). If the drive requirements are different (relative -Ug) than maybe it would not work that well without "revisiting" the values. But, since noone has tried 6V6 in the circuit so far, I am very interested to know whether it satisfies.
Regards,
Aleksandar |
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| Dave Cigna |
| quote: | Originally posted by Alex Kitic
To make a digression, the Darling amps somehow came to be
famous -- and I never understood why. |
The reason is very simple: they sound absolutely wonderful.
Incidentally, in my experience the shared cathode resistor tends to improve the soundstage, not shrink it. But, this is simply a matter of taste.
What I suggest is that you take a cliplead and connect the cathodes on one of your own amps to listen for yourself. It's a very simple experiment. Different amps tend to respond differently. Sharing the cathodes on an input stage will have a different effect than an output stage, &tc.
These are the kinds of things that are difficult to predict ahead of time by pure theorizing. One of my favorite pastimes is trying to explain the effect afterwards (so that we might predict in the future), but deciding what will sound best without listening is what has lead to a commercial wasteland of mediocre, flat sounding equipment. The stuff might be 'well engineered.' It might measure well and the circuits might be easy to defend, but they don't necessarily present the music well.
I think that creating a successful design requires a balance of theorizing and believing your ears. I don't think it is enough to rely completely on one or the other, but that is just my opinion!!
I suppose I could summarize my entire rant by saying that I would have to listen to both a mulligan and an rh84 before I could form an authoritative opinion about one being better than the other.
-- Dave Cigna |
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| Alex Kitic |
When it comes to the Darling amps, I am inclined to believe they must have something goog going on, since so many people have built them, and there seems to be a general agreement that they sound well indeed.
I recall downloading and reading with great interest a text about various Darling amps being listened to in public by a group of enthusiasts. While the 1626 is not something I might find in some tube stash in my surroundings -- what actually struck me was that people tend to live better lives :(. They seemed to be able to gather in numbers and enjoy their hobby together -- which is far from possible in reality where I live (the country being both small and low-income).
Well, while it seems that most Darling amps had common cathode resistors below the output tube (even below the driver tube), NONE of these, as I recall, was UNBYPASSED. It is important to stress this issue, since there is quite a difference between using a common resistor which is bypassed by an adequately sized cap (therefore in AC terms it should be like if the caps were not common at all, since there should be no or little signal interaction) -- and using a common resistor which is not bypassed, with obvious signal interaction.
Clipping the Rk's together -- not that I am really willing to open an amp and try that... but it might be a good idea, just for the sake of trying. Since Rk's are usually bypassed (in my case), I do not think that there would be much of a difference. Doing it with unbypassed caps... well, it would certainly give a flavour to the sound.
I also recall reading a letter posted to Sound Practices about the sonic merits of "blonde monsters" -- the hi-fi of yesteryear. The point was that some people prefer (and are obviously entitled to it) sound which is maybe not that true to the source, but suitable to their palats. And, there is no universal truth...
Finally, when it comes to "Mulligans" (why the name?) vs. RH84 -- probably like most of the others, I am waiting for someone to try it. It was tried once, a few years ago -- a friend's friend who built an RH84 (his RH84 can be seen on my web-site as "built by M.S.") has had the opportunity to compare it to a Zen clone built by a friend of his. I even have a picture of the two amps -- but it is somewhere in "old mail" and I would have to go to great lengths to find it (mail archive database, not active). I cannot vouch for any of the amps, since I have not seen them (except on a photo) nor heard them, and I recall the Zen clone to be built with an AZ50 rectifier (which obviously does not sound the same as 5U4G) -- but I recall that the Zen clone owner decided that he should remake his Zen clone into an RH84. This may sound inflamatory to some, but you can just consider it as an invitation to try -- with no hidden second toughts.
Regards to all,
Aleksandar |
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| Dave Cigna |
Aleksandar, of course we are talking about bypassed cathode resistors; I thought that would be assumed...
| quote: |
Clipping the Rk's together -- not that I am really willing to open an amp and try that... |
:confused: why not???
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