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?
Few examples I found:
http://www.bonavolta.ch/hobby/en/audio/el84.htm
http://www.tubeaudio.8m.com/RH84/rh84.html
http://www.angela.com/catalog/how-to/SE.EL34.html
TIA...
Also, is there a particular driver tube that sound good with the EL84?
Few examples I found:
http://www.bonavolta.ch/hobby/en/audio/el84.htm
http://www.tubeaudio.8m.com/RH84/rh84.html
http://www.angela.com/catalog/how-to/SE.EL34.html
TIA...
RockysDad said:
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.
Oh, wow.. Brain freeze...
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...
Re: Re: EL84 SE design recommendations?
Exactly. The things which the EL34 shares with the EL84 are:
- 6.3V heater (E)
- Output beam tetrode/pentode (L)
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...
Brett said:
Exactly. The things which the EL34 shares with the EL84 are:
- 6.3V heater (E)
- Output beam tetrode/pentode (L)
Brett said:
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...
Re: Re: Re: EL84 SE design recommendations?
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.
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.
Yes.RockysDad said:
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.
Yep.audiousername said:
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.
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.
@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.
Gday.
Another one:
http://members.at.infoseek.co.jp/lagarto/el84seamp.png
edit/
in above post, it is a EF86
Another one:
http://members.at.infoseek.co.jp/lagarto/el84seamp.png
edit/
in above post, it is a EF86
Attachments
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...
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...
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.
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.
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...
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...
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
)
Hmm... I don't know what to say anymore (A very good thing )
Good luck!
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
)Hmm... I don't know what to say anymore (A very good thing
) Good luck!
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...
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...
Have buildt the Decaware
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
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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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Re: Have buildt the Decaware
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)
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"!
Nice "Mulligan", Bjorn.
icebear said:
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)
icebear said:
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"!
Re: Re: Have buildt the Decaware
I know. It's made by Novarro (italian). Most likely not the best around, but ok. Cost 60 euros a pice.
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
audiousername said:
I know. It's made by Novarro (italian). Most likely not the best around, but ok. Cost 60 euros a pice.
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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