Opinions on 2A3 Push-Pull amps?

[PakProtector]

Negative feedback does not give you higher power, it gives you less gain, and most importantly, lower distortion.

It could be that the distortion reduction is a side effect, and the primary reason to employ it is for output impedance reduction. I can tell you that a solid, low distortion amp, that employs enough carefully applied NFB to deliver target output Z can deliver a fine amp.
cheers,
Douglas

 

[jusmee]

It could be that the distortion reduction is a side effect, and the primary reason to employ it is for output impedance reduction. I can tell you that a solid, low distortion amp, that employs enough carefully applied NFB to deliver target output Z can deliver a fine amp.
cheers,
Douglas

I agree. Forgot to mention the output impedance.

I will now turn around and also say that a single ended amp with no global neg feedback loops can still sound great in the right situation as well. Maybe not as technically accurate and distortion free, but very musically enjoyable.

 

[PakProtector]

And of course the NFB loop need not be global. Plate to grid for one, or plate to driver cathode( as in the RCA SP10 and SP20 ) amps come to mind.
cheers,
Douglas

 

[HowardK]

I recently built Pete Milletts PP 6b4 amp design using JJ 2a3's and UTC LS-55 opt and am amazed by the sound. If there is any one in the Houston area that has some 300b SE amps that we could compare PM me!

 

[dowto1000]

Negative feedback does not give you higher power, it gives you less gain, and most importantly, lower distortion.

You are 100% correct about lower distortion, but there is a cost of using negative feedback, always. It puts an out -of-time signal back to an earlier stage, mixing it in with a fresh new ( and different) incoming signal, and some folks don't like that sonically. Some will prefer a circuit that passes the signal only one time, through the amp.

Dowto1000

 

[jwoody]

I had a pushpull 2A3 integrated from Cary some years ago as a loaner amp, my speakers at the time were Alon Lotus SE's, I loved the amp it was astonishingly transparent and detailed, I was a detail freak back in those days, but my girlfriend said it was too bright, in her words "screechy". So back it went. The loaner was from Deja Vu Audio my local dealer, and their former tech had built quite a few pushpull amps from triodes.

I cannot remember if I heard a 2a3 amp specifically but about 18 months ago I had on loan from them one of their pushpull 45 amps. It drove my former speakers, original JMlabs Micro-Utopias, well not bright at all but the amp was detailed to the point of being distracting. A poor match with those speakers would love to hear them with my current AN-J's. I guess my takeaway is a pushpull 2a3's can be fantastic amps but need careful speaker matching. I've not heard a 2a3 set but both the amps mentioned were significantly better than my one foray into SET's, a pair of Cary 300B monos.

 

[dowto1000]

What an interesting thread !!

My very first speaker system I ever bought, ( after leaving Penn State for sunny California ), was a pair of 15 inch Tannoy Monitor Golds in GRF enclosures, about 1969.

My older brother heard mine, and also in 1969, bought the Tannoy M.G.'s, in their 12 inch driver size.

In 2018, I would say try a P-P 2A3 amp, ( not using biplates ) but the new JJ 2A3- 40 tube, built as with two tube stages, and with a Lundahl interstage transformer, and NO negative feedback loop. Run on AC for the filaments. It will possibly serve you well .......with your 15 inch Monitior Golds.

There is one very real additional design consideration, regarding a CCS on the cathode resistor of the driver stage's triode tube sections. You see, if someone knew how to execute the power supply properly, no CCS on the cathodes of the triode driver stage tube would be wanted, and this should sound best, certainly least " forced".

No one ( I have seen, DIYer, or a manufacturer ) has ever done this type of amp's power supply optimally. I am afraid, therefore, people today will obtain the best result reverting to adding a CCS on the Rk. of the driver tube. Its a band - aid.

If you DIY this design, do try to use low-as-possible DCR chokes, for 2A3s.

Since 1981, I always liked 20 Ohms or less in DCR for chokes, and to do this, it takes two L/C sections in series. I think this amp might sound really very good.

JJ 2A3 - 40s, using 2.5 VAC to heat the filaments,....... is " my " preference, ...gets my vote to try, since you have asked us. YMMV.

Have fun.

Dowto1000

 

[BillWojo]

6DZ7, I've even done the math for him when he claims it causes smearing, what ever that is but I was told I didn't know what I was talking about because I've never heard his amp and all my amps are severely compromised. ????? Even my MC40's are severely compromised with the feedback circuits. I guess that I like severely compromised amps. Go figure. LOL

BillWojo

 

[dowto1000]

6DZ7, I've even done the math for him when he claims it causes smearing, what ever that is but I was told I didn't know what I was talking about because I've never heard his amp and all my amps are severely compromised. ????? Even my MC40's are severely compromised with the feedback circuits. I guess that I like severely compromised amps. Go figure. LOL

BillWojo

Hi Bill,

I would like to say this in a "loving" and non offensive way, which is hard to pull off.

The constant, between what you discuss above, in our exchange " way back when", and what you choose to post about me today, is still the same !!

You still have never heard one of my amps, nor, much better yet, have you ever attended a RMAF to hear one of Dennis' 2A3 DC amps, and how nicely his perform.

Nothing....since then, has changed - at all. Yes, you have no direct listening experience, with what is possible.

Other than that, my very best to you !! Happy listening.

Dowto1000