Opinions on 2A3 Push-Pull amps?
- Thread starter seanrr
- Start date
PakProtector
AK member
That is an interesting definition of 'painfully loud'. I would apply it fairly comfortably to a tri-amp system delivering about 110W into horn-loaded, efficient drivers( EVM-12L for bass, DL10x for lower mids, and RCA MI-9584 for the upper end ).
cheers,
Douglas
PakProtector
AK member
Oh yes, I am quite familiar with that sort of 'take' on SE. And his amps.
cheers,
Douglas
Fast-forward 15 years and his top four amps are all push-pull....
Poultrygeist
Lunatic Member
SET amps are a niche market.
seanrr
Well-Known Member
Buy - I saw one on that auction site built by a guy in Canada - I am not sure about the quality, but it looks quite nice. But, before I pull the trigger, I am contemplating whether it would make more sense to invest in upgrading a 300b SET amp I have instead. I think upgrading the transformers on the 300b might improve it considerably since I have a similar SET amp made by the same guy with different transformers, which is MUCH more to my liking...
I am tempted by 2A3 PP since I have heard that it provides cleaner base while maintaining some of that SET magic, but I have never heard one.
As far as SET amps being a niche market, there is no question. However, once you have gotten into a nice SET system, it is difficult to go back to something else (at least in my experience).
Just to be clear: that's a marketing document NOT a technical article.
Personally, my goal right now is to design and build a PP amp that has all the transparency of my two stage direct coupled 300B SET. I have tried with several PP 6P14P-EV amps that just don't make it, but I am now attempting a PP 6V6 amp and a PP 6A5G amp. Only time will tell....
Poultrygeist
Lunatic Member
Doesn't help Steve sell his push pulls does it?
Maybe consider a differential output stage with a CCS in the tail. Kevin Carter at K&K builds designs like this. I've been using this scheme for nearly 10 years and I love it. You need a good class A bias point and it forces AC balance. The first time I tried it I couldn't believe the improved low level clarity improvement. It does give a harder clipping at full power so you need to be sure you have enough power for your needs because it won't overload as softly as a regular tube output stage.
Good luck with your project,
John
He wasn't selling any PP amps when he wrote it.
Joe Roberts
Agent Provocateur
Push pull triode amps are more of a niche market than SE. How many commercial ones are there and how many are built DIY vs. more popular SEs?
Anyway, this thread and the topic itself are awash in rampant speculation. I know...what else can ya do?
You can look at speaker specs all day long and you will not know how it sounds hooked up to three watts and what you are missing or not by moving up to say 20W.
You can't discover whether an amp is going to be good or meet certain unique requirements by employing nomenclature like "2A3 PP" or worse yet in terms of variability, 300B SE.
Even before the speaker compatibility question enters the picture, you have to dial in on which particular amp we're discussing.
In regards to this specific case, I'd say if the OP has an underperforming 91 style amp, the economic and practical thing to do would be to upgrade that, especially if it has some junky aspects at present.
Still. I think a good 2A3 PP might have tighter and punchier bass than many 91 implementations, especially speakers that seem to want a little more juice. That old 91 amp usually works out to sounding fairly lush and bouncy rather than punchy, especially with marginal quality transformers.
A 300B SE with a stout low impedance driver stage instead of a pentode, a stiffer power supply, and wideband iron can sound ultra precise and dynamic, but a 91 is not headed in that direction. I liked the good 91s I built for their color and texture and flow rather than bass slam.
At the company where I work, specialized in 300B amps, I've heard 10-12 balls to the wall implementations over the past 20 years--direct coupled,silver wire and silver foil secondary transformers, Bendix 6900 drivers, nickel and finemet cores, some with regulated supplies, insane driver stages. Crazy stuff. This kind of amp is very high definition and has a lot of drive but they come out very different in character with the design changes.
So, at this point, the concept of "A 300B SE" has nothing to hold on to for me. I have to ask "Which 300B SE?" The pie is infinitely divisible.
Same with PP 2A3, although there are a lot fewer of those around and most do not yet exist, you would have to build it. My experience suggests that there is a lot of potential in this arena that I need to get back to.
I can't advise on commercial products since I don't pay any attention to what's out there but there is a lot of cool stuff one can build.
Anyway, this thread and the topic itself are awash in rampant speculation. I know...what else can ya do?
You can look at speaker specs all day long and you will not know how it sounds hooked up to three watts and what you are missing or not by moving up to say 20W.
You can't discover whether an amp is going to be good or meet certain unique requirements by employing nomenclature like "2A3 PP" or worse yet in terms of variability, 300B SE.
Even before the speaker compatibility question enters the picture, you have to dial in on which particular amp we're discussing.
In regards to this specific case, I'd say if the OP has an underperforming 91 style amp, the economic and practical thing to do would be to upgrade that, especially if it has some junky aspects at present.
Still. I think a good 2A3 PP might have tighter and punchier bass than many 91 implementations, especially speakers that seem to want a little more juice. That old 91 amp usually works out to sounding fairly lush and bouncy rather than punchy, especially with marginal quality transformers.
A 300B SE with a stout low impedance driver stage instead of a pentode, a stiffer power supply, and wideband iron can sound ultra precise and dynamic, but a 91 is not headed in that direction. I liked the good 91s I built for their color and texture and flow rather than bass slam.
At the company where I work, specialized in 300B amps, I've heard 10-12 balls to the wall implementations over the past 20 years--direct coupled,silver wire and silver foil secondary transformers, Bendix 6900 drivers, nickel and finemet cores, some with regulated supplies, insane driver stages. Crazy stuff. This kind of amp is very high definition and has a lot of drive but they come out very different in character with the design changes.
So, at this point, the concept of "A 300B SE" has nothing to hold on to for me. I have to ask "Which 300B SE?" The pie is infinitely divisible.
Same with PP 2A3, although there are a lot fewer of those around and most do not yet exist, you would have to build it. My experience suggests that there is a lot of potential in this arena that I need to get back to.
I can't advise on commercial products since I don't pay any attention to what's out there but there is a lot of cool stuff one can build.
PakProtector
AK member
There are all sorts of 'pentode' front ends. The typical high gain stuff, like 6SJ7/6AU6/EF86...all counting on ridiculously high plate loads to deliver gain at the low delivered gm. Or at the other end, 6BQ5/6CL6/6V6 that when loaded with resistors similar to their usual tx-coupled plate loads can do pretty well indeed. Stuff like the Citation II which ran 12BY7, which falls towards the latter...
cheers,
Douglas
cheers,
Douglas
Poultrygeist
Lunatic Member
Makes you wonder why it's still there then? Selling PP amps for Steve was a business decision. I know the guy.
Because it's marketing for his SE amps, as Pak said above, also a business decision. I've had a Decware SE amp for a long time, it's a good amp and works well with my Altecs. I'm familiar with Steve as well. I can't say I've experienced the horrors of PP as described by Steve, in fact my 60yo PP monoblocks provide a more satisfying experience overall for my taste and the Decware amp lives in its box. Certainly it does some things very well, better than my PP amps, but with the experience of hearing a number of amps over the years I can recognize that Steve's white papers are largely enthusiastic marketing.
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Poultrygeist
Lunatic Member
Decware started with this and it's still Steve's favorite.
That's a couple of generations after the original and "B" models, but of course he likes his products and is proud of them. Fifteen years ago he wasn't saying that was his best amp and I'm sure he's not saying the same thing about PP as a topology now as he was back then. I'm going to go out on a limb and guess that he thinks his PP amps are better than others', but what exactly are we arguing here?
Decware started with this and it's still Steve's favorite.
Poultrygeist
Lunatic Member
PakProtector
AK member
Yah...no kidding on the 'Marketing' paper.
That said, I would be quite comfortable putting a multi-grid final amp up against a PP 2A3 amp any day ov the week. I have on at least one occasion delivered design and assistance for an 807 amp that relegated a solid 2A3 design to paperweight duty. An EL84/6Pi14Pi-EV amp should have no issue doing the same thing...LOL Especially one using EL84's as signal tubes too.
As Joe said, it is all in what you use to build it, and in what path the electrons flow.
cheers,
Douglas
Joe Roberts
Agent Provocateur
AND the speaker.
In fact, it's everything...the whole system.
I can surely believe that some, indeed most, speakers work far better with PP807s than 2A3s. Very few speakers really come alive on 6 or 8 W. Fewer still will play loud and with commanding bass on real low power. Sound will come out of any speaker using a 2A3 though and assess it on its merits or lack thereof.
I love the sound of low powered triode amps but you can hit the stops with most box speaker/triode amp combos if you play them loud. Still, there are enough positive possibilities that low power is a viable path for many, even if the setups aren't perfect in every way.
PP 300Bs can be nice. One of the coolest experimental amps we developed was a pair of monster PP 300B monoblocks with an DC coupled topology that could waffle the grids to something like 27W peaks in A2. Huge, rock solid, crystal clear sound. Maybe it was a bit less sophisticated than our best 300B SE, but that depends on what you mean by "sophisticated!" A strong amp in its own right.
Negative feedback does not give you higher power, it gives you less gain, and most importantly, lower distortion.