alexg said:My new 12au7 cathode follower preamp. Tube rectified, tube regulated PSU, I use one 12au7 for the voltage amp for both channels and another 12au7 for the cathode follower stage, it gives me better tube rolling options!
Do you have a schematic available? I'm planning on starting a 12au7 preamp, or maybe something between that and 12ax7, soon but I haven't decided on a design. Will be my first tube project so I'd like to use a design that's already been vetted.
A (belated) reply to cycline3's post #2080
A wise man once said that you can either remain silent and risk people thinking you are ignorant, or open your mouth and prove it. You chose the latter with your post.
Instead of your strange, disjointed rant about me being a " n00b" who works in Wendy's, you might have just asked how the 6kOhm primary impedance of the OPTs was selected. I looked at a number of established 300B PP designs, of which two stood out. One was Lynn Olson's meticulously documented Aurora amps; he uses custom-wound 6.6kOhm OPTs. You know all about those amps, their evolution and Olson's reputation in general, right? I ask because I noticed that despite all the wind you generated, you never said what you believe is the correct OPT primary impedance for 300Bs operated in PP Class A. Could it be that you don't know?
Another highly regarded design is the one by Kevin Kennedy that was published in Vacuum Tube Valley; he used Citation II OPTs (4.4 K) and recommended Bertolucci 123s (4K) as alternatives. Other designs centered on 6kOhms primary impedance on the basis that is was twice what typically would be used with a single 300B operating in SE. I'm sure you know Kennedy's work thoroughly, and have carefully followed his reasoning w/r/t 300B PP output stages, correct? Good; then you can explain why an OPT with three times the impedance he used would be appropriate here.
You didn't bother asking anything about where the transformers were wound, either. Jack Elliano of ElectraPrint made the final choice on primary impedance before he wound the OPTs. A super-experienced tube whiz like you must know that company well; I am certain that Jack has forgotten more about tubes in general, and transformers in particular, than you likely will ever know.
The main purpose of my post was to ask for the reasoning behind selecting 12K as a primary impedance, something I've never seen before in any published schematic. You were too busy ridiculing me and my post to answer that question, most probably because you don't even know the answer.
This usually is a very congenial place, with content-free sniveling like yours a rarity. But your peculiar and condescending rant demanded an appropriate response.
A wise man once said that you can either remain silent and risk people thinking you are ignorant, or open your mouth and prove it. You chose the latter with your post.
Instead of your strange, disjointed rant about me being a " n00b" who works in Wendy's, you might have just asked how the 6kOhm primary impedance of the OPTs was selected. I looked at a number of established 300B PP designs, of which two stood out. One was Lynn Olson's meticulously documented Aurora amps; he uses custom-wound 6.6kOhm OPTs. You know all about those amps, their evolution and Olson's reputation in general, right? I ask because I noticed that despite all the wind you generated, you never said what you believe is the correct OPT primary impedance for 300Bs operated in PP Class A. Could it be that you don't know?
Another highly regarded design is the one by Kevin Kennedy that was published in Vacuum Tube Valley; he used Citation II OPTs (4.4 K) and recommended Bertolucci 123s (4K) as alternatives. Other designs centered on 6kOhms primary impedance on the basis that is was twice what typically would be used with a single 300B operating in SE. I'm sure you know Kennedy's work thoroughly, and have carefully followed his reasoning w/r/t 300B PP output stages, correct? Good; then you can explain why an OPT with three times the impedance he used would be appropriate here.
You didn't bother asking anything about where the transformers were wound, either. Jack Elliano of ElectraPrint made the final choice on primary impedance before he wound the OPTs. A super-experienced tube whiz like you must know that company well; I am certain that Jack has forgotten more about tubes in general, and transformers in particular, than you likely will ever know.
The main purpose of my post was to ask for the reasoning behind selecting 12K as a primary impedance, something I've never seen before in any published schematic. You were too busy ridiculing me and my post to answer that question, most probably because you don't even know the answer.
This usually is a very congenial place, with content-free sniveling like yours a rarity. But your peculiar and condescending rant demanded an appropriate response.
A few pics of the SimpleSE I just finished. It uses a ccs-loaded ecc99 driver tube and is a straight power amp. I don't think the ecc99 needs the CCS, but it was part of the circuit with the 12at7 so I thought I'd give it a try with CCS. I increased the current that the ccs supplies to just over 20 mA to better suit the ecc99 and left out the volume pot, other than that its a regular SimpleSE. It also has switches for cfb and ul operation. Some of the parts I used are Tung Sol 6550 power tubes, James OPTs, Electraprint custom choke, Riken, Kiwame and AN resistors, Mundorf SOI coupling caps and Vampire connectors. I wired it with mil spec silver plated teflon wire and Jupiter silver wire for the inputs.
I'm very happy with it so far, its powering Omega XRS speakers (these are fantastic speakers!), an Anthem Pre1 Preamp and Audio Alchemy reclocker/dac combo are upstream. Its replacing a Trends T-amp and so far is a great improvement. There is a slight ground loop hum that I need to figure out how to get rid of....
I'm very happy with it so far, its powering Omega XRS speakers (these are fantastic speakers!), an Anthem Pre1 Preamp and Audio Alchemy reclocker/dac combo are upstream. Its replacing a Trends T-amp and so far is a great improvement. There is a slight ground loop hum that I need to figure out how to get rid of....
chrish said:
Thanks, the ecc99 has lower mu than the ecc81, and my preamp has quite a bit of gain. Another guy living near me has a SimpleSE with the ecc81 driver and most of the same parts I used, so I should get a chance to compare them. Also, the ecc99 looked like it would be more linear than the eccec81, which is why i think ccs loading might not be needed (and also since I don't need more gain).
Also, I got rid of the ground loop hum by connecting the chassis of the preamp to the amp with a 12g wire... I'm guessing this is ok?
my unfinished project:
http://nagi.ee/photos/ResR/6385159/
Tubes have connected only heating elements with scrapped tube-tv transformer�Ls 6,3V secondary. Except the scrapped 6E1„P, it has a anode voltage directly from 230V through recitifier, what consist two scrapped 6X1„P and old capacitors. One 6E1„P don�Lt work well and i don�Lt have enough money to buy new ones.
http://nagi.ee/photos/ResR/6385159/
Tubes have connected only heating elements with scrapped tube-tv transformer�Ls 6,3V secondary. Except the scrapped 6E1„P, it has a anode voltage directly from 230V through recitifier, what consist two scrapped 6X1„P and old capacitors. One 6E1„P don�Lt work well and i don�Lt have enough money to buy new ones.
Mea culpa
Well, I see my response was a little too heated; in particular, I didn't mean to give the impression of dissing people working at a certain level out in the real world. There's dignity in any job well done. I'd still like to know why 12 kOhm OPTs were used . . .
Back to the point of this place: incredible woodworking on the SE amp, davec; however, aren't hose Mundorf caps a bit on the super-$pendy side? do you find them a big improvement over, say, Solens?
One of my favorites here, though, is Sjef's way back at post 18 because I've been looking for a small, easily moved PP amp to use out in the yard on sunny days with streaming audio and a pair of decent monitor speakers. That amp looks like a little EL84 version (though where are the input and phase-splitter tubes?); I wonder if its creator is still around and if so, could spare a schematic. TIA.
Well, I see my response was a little too heated; in particular, I didn't mean to give the impression of dissing people working at a certain level out in the real world. There's dignity in any job well done. I'd still like to know why 12 kOhm OPTs were used . . .
Back to the point of this place: incredible woodworking on the SE amp, davec; however, aren't hose Mundorf caps a bit on the super-$pendy side? do you find them a big improvement over, say, Solens?
One of my favorites here, though, is Sjef's way back at post 18 because I've been looking for a small, easily moved PP amp to use out in the yard on sunny days with streaming audio and a pair of decent monitor speakers. That amp looks like a little EL84 version (though where are the input and phase-splitter tubes?); I wonder if its creator is still around and if so, could spare a schematic. TIA.
Re: Mea culpa
Thanks for the compliment. I haven't done enough cap rolling to be able to do any comparisons, this is my first DIY amp. However, there are only 2 coupling caps in the circuit, so I only had to buy 2, and I think they were about $35 (for both) on sale from partsconnexion. Its one of the higher end parts I used, but reviews on these coupling caps seem to be consistently good. The amp did end up costing more than I had in mind, but I'm very happy with it
tomsyl said:
Thanks for the compliment. I haven't done enough cap rolling to be able to do any comparisons, this is my first DIY amp. However, there are only 2 coupling caps in the circuit, so I only had to buy 2, and I think they were about $35 (for both) on sale from partsconnexion. Its one of the higher end parts I used, but reviews on these coupling caps seem to be consistently good. The amp did end up costing more than I had in mind, but I'm very happy with it
Re: A (belated) reply to cycline3's post #2080
Hi tomsyl,
You tell him!
But I think you're a little confused. I am the one who selected 12K as the Zpri for my 300B PP amplifier. You asked a legitimate question, and some other jerk jumped in and attacked you for a lack of knowledge. That was not me, and I think my legitimate answer was lost in the flash and smoke.
So here it is again, why I chose 12K Zpri. Because, driving my JBL 4312 3 way box speakers, it sounds better than lower impedance primary settings. I am using a tapped transformer, so I can vary the Zpri up and down and evaluate the sound. This setting sounds best. I tried higher current, lower impedance and it just didn't sound as good.
Here's an engineering argument. The 300B has an anode resistance of about 800 ohms. The damping factor of 800 ohms plus another 100 ohms DCR driving into 3K ohms is approximately 3.3. This results in a bass-heavy and muddy sound on a lot of speakers. It may work better with horns or OBs but box loaded woofers seem to like higher DF. I'm about to experiment with the horns and dipoles to find out for myself whether a lower DF ican be tolerated.
The reason for designing to a lower DF in the first place is higher power output. But I find that the difference between DF=4 and DF=6 for 300Bs is hardly noticeable in volume or headroom, but is a huge difference in tightness of the bass response.
On SE amps, the lower DF may also introduce more second harmonic loudness cue in the signature, which may be a good thing sonically if the bass doesn't blow out.
The attached image from the WE 300B data sheet specifies load impedance from 1K5 to 6K5, plate voltage from 200 volts to 450 volts, and standing current from 30mA to 80 mA, with many perfectly reasonable operating points all along the range. You can get a copy of the data sheet at Pete Millett's site:
http://www.pmillett.com/tubedata/we300a_b.pdf
I don't think it can be categorically stated that the current popular operating points are the best sounding for 300Bs. My experience tells me otherwise, but then it may come down to a particular speaker, and the rated impedance doesn't provide enough information to derive more than a starting guess.
Anyway, I'll bet your 300B PP amplifier is going to sound wonderful. Just build it and don't worry too much about the design decisions and particularly don't worry about random opinions on the forum.
Cheers!
Michael
tomsyl said:
Hi tomsyl,
You tell him!
But I think you're a little confused. I am the one who selected 12K as the Zpri for my 300B PP amplifier. You asked a legitimate question, and some other jerk jumped in and attacked you for a lack of knowledge. That was not me, and I think my legitimate answer was lost in the flash and smoke.
So here it is again, why I chose 12K Zpri. Because, driving my JBL 4312 3 way box speakers, it sounds better than lower impedance primary settings. I am using a tapped transformer, so I can vary the Zpri up and down and evaluate the sound. This setting sounds best. I tried higher current, lower impedance and it just didn't sound as good.
Here's an engineering argument. The 300B has an anode resistance of about 800 ohms. The damping factor of 800 ohms plus another 100 ohms DCR driving into 3K ohms is approximately 3.3. This results in a bass-heavy and muddy sound on a lot of speakers. It may work better with horns or OBs but box loaded woofers seem to like higher DF. I'm about to experiment with the horns and dipoles to find out for myself whether a lower DF ican be tolerated.
The reason for designing to a lower DF in the first place is higher power output. But I find that the difference between DF=4 and DF=6 for 300Bs is hardly noticeable in volume or headroom, but is a huge difference in tightness of the bass response.
On SE amps, the lower DF may also introduce more second harmonic loudness cue in the signature, which may be a good thing sonically if the bass doesn't blow out.
The attached image from the WE 300B data sheet specifies load impedance from 1K5 to 6K5, plate voltage from 200 volts to 450 volts, and standing current from 30mA to 80 mA, with many perfectly reasonable operating points all along the range. You can get a copy of the data sheet at Pete Millett's site:
http://www.pmillett.com/tubedata/we300a_b.pdf
I don't think it can be categorically stated that the current popular operating points are the best sounding for 300Bs. My experience tells me otherwise, but then it may come down to a particular speaker, and the rated impedance doesn't provide enough information to derive more than a starting guess.
Anyway, I'll bet your 300B PP amplifier is going to sound wonderful. Just build it and don't worry too much about the design decisions and particularly don't worry about random opinions on the forum.
Cheers!
Michael
Attachments
Thanks a ton, Michael - just what I was looking for.
I realized that it was your design, and was actually asking you about the highish OPT impedance when I got distracted and spent my energy sounding off towards a flame job from another poster.
That type of experimental data is really useful to me. I noted that way back when the 300A was first released by WE, its data sheets specified 4K as the output impedance for a pair in A2 PP, so that was a target of the few old-time designs that used it. And I understand generally the tradeoffs between power out, damping factor and distortion with increased output impedance, but it's very helpful to have the theory empirically proven with your experiments.
I don't have the luxury of a tapped OPT (and I remember reading somewhere that in certain applications they can be suboptimal unless you use the highest or "outside" tap) so I had to pick a number. My focus is on something that will drive a number of speakers I have lying around with lowish efficiencies (unlike your JBLs) but still sound good, so I went for 6K as something of a compromise. What I'm really looking for is an amp that will drive a broader range of speakers while hopefully preserving some of the character I get such a kick out of with my 300B SE amp's measly 8 watts and poor damping factor. There is only one way to find out . . .
Thanks for the inspiration to get this one off the drawing board and start drilling and cutting some metal.
I realized that it was your design, and was actually asking you about the highish OPT impedance when I got distracted and spent my energy sounding off towards a flame job from another poster.
That type of experimental data is really useful to me. I noted that way back when the 300A was first released by WE, its data sheets specified 4K as the output impedance for a pair in A2 PP, so that was a target of the few old-time designs that used it. And I understand generally the tradeoffs between power out, damping factor and distortion with increased output impedance, but it's very helpful to have the theory empirically proven with your experiments.
I don't have the luxury of a tapped OPT (and I remember reading somewhere that in certain applications they can be suboptimal unless you use the highest or "outside" tap) so I had to pick a number. My focus is on something that will drive a number of speakers I have lying around with lowish efficiencies (unlike your JBLs) but still sound good, so I went for 6K as something of a compromise. What I'm really looking for is an amp that will drive a broader range of speakers while hopefully preserving some of the character I get such a kick out of with my 300B SE amp's measly 8 watts and poor damping factor. There is only one way to find out . . .
Thanks for the inspiration to get this one off the drawing board and start drilling and cutting some metal.
Very neat, ollebolle
though that power transformer looks a little unusual to these rustic American eyes. %^>
I love small SE amps in general and those using the EL-84 in particular. Is the 220 ohm resistor a grid-stopper, meaning it should be mounted right on the tube socket with a very short lead?
Also, are you able to give the power output (I'm assuming about 2-4 watts), and whether it would be a complex task to double it by adding another EL-34 and lowering OPT impedance to 2.2 Kohm, a value of which I happen to have two of? TIA.
though that power transformer looks a little unusual to these rustic American eyes. %^>
I love small SE amps in general and those using the EL-84 in particular. Is the 220 ohm resistor a grid-stopper, meaning it should be mounted right on the tube socket with a very short lead?
Also, are you able to give the power output (I'm assuming about 2-4 watts), and whether it would be a complex task to double it by adding another EL-34 and lowering OPT impedance to 2.2 Kohm, a value of which I happen to have two of? TIA.
Re: Very neat, ollebolle
Yes, the 220 ohm is a grid-stopper! I hadn't heard that it should be mounted very near the tube, but I'm shure it's tru if you say so!
Lucky me, mine is just a few millimeters from the pin on the socket
The constructor, (Alex) wrote on this forum somewere that it gives 4WRMS.
I don't have an answer about your parallell question, but i'm sure someone else does
tomsyl said:
Yes, the 220 ohm is a grid-stopper! I hadn't heard that it should be mounted very near the tube, but I'm shure it's tru if you say so!
Lucky me, mine is just a few millimeters from the pin on the socket
The constructor, (Alex) wrote on this forum somewere that it gives 4WRMS.
I don't have an answer about your parallell question, but i'm sure someone else does
Tubelab SE amp finished.
After a bit of bumpy start seen here, it is finally finished and I like the way it sounds. My main concern was noise floor because of my 105 db horn driver but to my delight, there is no hum at all. List of visible components are as follows.
Output transformers: Electra-print, 3K Ohm, 100 mA, 15 watt rated
Output tubes: Valve Art 300B
Power transformer: Hammond 272JX
Input tubes: Raytheon 5842
Rectifier tube: JJ Electronics 5AR4
The rest are purchased from Mouser and Digikey.
Here are the photos.
After a bit of bumpy start seen here, it is finally finished and I like the way it sounds. My main concern was noise floor because of my 105 db horn driver but to my delight, there is no hum at all. List of visible components are as follows.
Output transformers: Electra-print, 3K Ohm, 100 mA, 15 watt rated
Output tubes: Valve Art 300B
Power transformer: Hammond 272JX
Input tubes: Raytheon 5842
Rectifier tube: JJ Electronics 5AR4
The rest are purchased from Mouser and Digikey.
Here are the photos.
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.
An externally hosted image should be here but it was not working when we last tested it.
