2A3 SE or PP & Bottlehead or DIY?

Hi.

I'm lucky enough have been given 4 x NOS RCA 2A3 Tubes still in their boxes and want to build an amp around them. I really like the simplicity & reasonable price of the Bottlehead Monoblock Paramount kits and they seem to get rave reviews all over the place. Problem is that because I have the four Tubes I'd love to use them all in the design but of course that means I'll be running PP instead of SE of which I'm led to believe is 'purer'.

I already have a decent collection and large range of SS Amps and a few great sounding yet fairly standard PP Tube Amps plus I have many different styles and ages of speakers. I haven't yet explored the world of high quality, low powered SE Amps & suitable high efficiency speakers and I'm thinking that building up a pair of Paramounts to use a couple of my 2A3s may be a great way into that area but I also feel that would be a waste of the other two 2A3s too. They're obviously worth more in a quad set but I don't really want to sell them either. I've seen a few circuits around to build PP 2A3 Amps using two tubes per channel but I'm not sure if they would output an equivalent quality compared to the Bottlehead or other SE designs. I'm a great solderer and can fumble my way around fixing the basics of an existing SS or Tube Amp but I'm the first to admit I have a loooong way to go before I understand all the ins & outs of amplifier design which is another reason the kit is attractive.

Hmmm, can anyone help me with this '1st world' dilemma? Any advice welcome, cheers.

I just sold my Bottlehead Stereomour 2a3 integrated...

...To upgrade to a set of Paramounts. From my personal experience I would say that you absolutely should build a Bottlehead kit, but only if you have the right speakers.

Maybe look at designing/building a SET (1 output tubes per channel) with the capability to also run in SEPT (two output tubes in parallel per channel). That way you can try out parallel SET for more power and compare it to standard SET.

OTOH, for a lot less work & cost, you could just go with SET from the get go and have a spare pair ready for when you've put too many hours on it because you enjoy the SET sound...

marantzfan said:

From my personal experience I would say that you absolutely should build a Bottlehead kit, but only if you have the right speakers.

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Cheers for that. That's a tick in the Bottlehead column. For an SE beginner and in your opinion, what would be an example of a pair of affordable yet effective speakers to really demonstrate the qualities of SE-ness. Fullrange kit from PE, possibly go down the DIY OB path perhaps or are there nice little prebuilt units I can get for a few hundred?

Tinkerbelle said:

Maybe look at designing/building a SET (1 output tubes per channel) with the capability to also run in SEPT (two output tubes in parallel per channel). That way you can try out parallel SET for more power and compare it to standard SET.

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Ahh, now you're talking! See, I had no idea you could parallel them Any real benefit to doing this or would it really just be quasi-wasting a pair of decent tubes you think? I could also just use two tubes and have two spares... but where's the fun in that?! Seriously though, I thought a decent SE Amp running decent quality tubes would literally last for decades before needing to think about tube replacements as they're not being pushed very hard... or do I have that all wrong?

SteveAndBell said:

Cheers for that. That's a tick in the Bottlehead column. For an SE beginner and in your opinion, what would be an example of a pair of affordable yet effective speakers to really demonstrate the qualities of SE-ness. Fullrange kit from PE, possibly go down the DIY OB path perhaps or are there nice little prebuilt units I can get for a few hundred?

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Well, for 2A3, I personally wouldn't choose a speaker that is less than 97db sensitive unless you are either listening in near field or in a small room. A lot of fellas that are into low power SET like using Altec, Klipsch and other horn speakers due to their high sensitivity. I personally like Altec Duplexes the best and there are several others on AK that like them too.

That tube IMO is best used as SE. Get you some high efficiency Klipsch speakers and build a pair of SE mono blocks. The bottlehead stuff is good, I've built several myself. Save your spare tubes for one day down the road.
I have several SE amps and love my Cornwalls for the price, they are hard to beat.

Again, just my opinion.
Mark

Single ended and those 3 watts will go a long way ( 93 db speakers and above ). Still enamored with my 2a3 Bottlehead Paramours.

I would go with Asian practices, like no lytics, etc.... There's a good one in an old SP magazine which are online now.

Personally, I'd also just go SET and save the second pair for your spares. If you'd consider a very simple, great sounding design, I built one with help from Dennis Had, founder of Cary Audio. And total cost of parts is under $500...:thmbsp:









http://www.audiokarma.org/forums/showthread.php?t=503096&page=4

Sorry everyone, but I vote for PP with a long tail pair driver like the Poindexter Music Machine. I've built one using 6B4G (6.3V version of 2A3). It's got great bass and is crystal clear. Very nice low level detail and still smooth as silk sounding.

http://www.6moons.com/audioreviews/audiotropic2/machine.html

http://www.diyaudio.com/forums/tube...ding-poindexters-6gk5-el34-music-machine.html

Have fun,
John

Well, I am happy to see a good divergence of opinions here: that's healthy for the forum.

I think that a SE 2A3 Bottlehead kit is the quickest route to good sound and may even be the most cost effective. That said, whether the OP goes for SE 2A3, SE parallel 2A3 or push pull 2A3, very efficient speakers are absolutely mandatory for excellent sound with realistic dynamics and powerful bass. There is just no way around the physics of it. I ran a pair of 93dB Tannoy speakers for a year using SE2A3 and SE300B amps and when I finally replaced them with my 100dB+ Altecs it was a huge relief. The Tannoys had sounded GOOD, but the Altecs were in another league. I just can't live without the dynamics of real music.

Anyway, I am guessing that most of those advocating for SE 2A3 have never heard PP 2A3. The reason to go PP is not for the added power as it is negligible, the reason is for excellent sound. While the SE amps can have a slight edge when it comes to transparency and detail, the PP amps come in with high marks for having a “presence” that is hard to define. Let’s just say they are fun: if the SE amps are Pink Floyd then PP amps are NRBQ.

In the end it is hard to mess up a SE 2A3 amp but very difficult to get a PP 2A3 amp right. Probably the best approach for a 2A3 PP amp would be to use the Simple Push-Pull (SPP) Board from Tubelab.

Whatever you decide, don't cheap out on the output transformer. Assuming you have a competent power supply, it is the most important component in the amp.

This is the (not so simple) PP 2A3 amp I am working on:

I bought Marantzfan's Stereomour. There's an immediate difference compared to the PP amp we were using. It will be tough not moving up the chain,,,,,,next week.

Thing about SET is you can make it as simple or complex as you like. A lot of folks like the minimalist approach, I tend to go for a higher parts count. But yeah, don't cheap out on the OPTs, that's the soul.

jaymanaa said:

Thing about SET is you can make it as simple or complex as you like. A lot of folks like the minimalist approach, I tend to go for a higher parts count. But yeah, don't cheap out on the OPTs, that's the soul.

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Plus, they do most of the heavy lifting -- for best results, they need good, full frequency response at "full power" and they have to deal with the DC plate voltage without saturating (unless one employs, e.g., a parallel feed topology to spare them from that ignominy).

oh, and as to the original question -- I'd recommend stickin' with single-ended topology. If the OP really, really needs more power (shades of Tim "The Toolman" Taylor!)... paralleled 2A3s (or DH triodes capable of more output power SE, such as the 300B or some of the big, somewhat evil transmitter tubes) would, I'd opine, be the preferable route.

I say, take with a good 2A3 amp is capable of (which is plenty, within the context of 3-ish watts output) and invest in loudspeakers that will make the most of it.

Since this isn't a particularly inexpensive rabbit hole -- I'd also recommend spending some quality time listenin' before sinkin' cold, hard lucre into the venture.

meshplate2A3 by mhardy6647, on Flickr

I like straight-up 2A3 SET best - simple is good, less (parts count) is more.

BUT, I wouldn't pass go or spend dollar 1 till I had the speaker challenge solved and with 3.5w, it's a big challenge. For me, 2A3 starts to really shine with speakers up around 100db efficiency and my favorite in regular sized rooms are Altec duplexes (604s).

Excellent info here guys, thanks!

It's looking more and more like the Bottlehead kit would be my best bet to introduce myself to the world of low powered SE while reaping the benefit of the gifted 2A3s. As I already have a few other Tube Amps (including these silly OTT 100W Russian beasts http://www.audiokarma.org/forums/showthread.php?t=585342) I'm really looking forward to the simplicity of the build and the purity of the output as I have nothing else anywhere near this league plus this would be a great way of learning more about how these glorious devices work.

Yes, getting a pair of Altecs will be on the todo list however I think I may already have a few speakers that should be sensitive enough to work well with the 2A3s initially. Best bit about doing it this way is that it gives me the opportunity to tinker and compare the differences and that's what I like the most about this hobby :thmbsp:

You could build (4) 2A3 SET amps, drive them with a pre that has dual outputs and then bi-amp your speakers. Adding an active crossover between the pre and the amps would help get the most out of the amps.

Just a thought....

The quality of the iron is the most important thing in any 2A3 amp. If you are going to build your own, I would not buy a Bottlehead - I would spend some time finding a buddy/guru in your area, and slowly gather the needed parts to build an outstanding amp. D

I have both SET and PP 2A3s in the house right now, and they both are topnotch. But they are built with an uncompromised level of parts. The Bottlehead is good, but it has its limits due to economic necessity.

Agree with Dave - output iron is big-time important with these and Bottlehead is built to a price point.

marantzfan said:

Well, for 2A3, I personally wouldn't choose a speaker that is less than 97db sensitive unless you are either listening in near field or in a small room. A lot of fellas that are into low power SET like using Altec, Klipsch and other horn speakers due to their high sensitivity. I personally like Altec Duplexes the best and there are several others on AK that like them too. [emphasis added]

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Naah... really!?

;-)

In seriousness -- the OP might find slightly lower sensitivity speakers are acceptable depending on the room and taste in music (and preferred listening level). I think as stuff sounds better and better, the need to listen LOUD actually decreases -- and it's astonishing how good an SE 2A3 amplifier and a high sensitivity speaker can sound at very low levels (e.g., fade-outs on recording stay full and rich sounding "all the way out" at my house on most recordings).

At any rate, my point (and I really did have one!) was gonna be -- if the OP develops a taste for extended range (so-called "fullrange") drivers requiring no electronic crossover or contouring components in the speaker design itself... a few dB less sensitivity than quoted above may be fine. Case in point, some of the Fostex "fullrange" drivers (e.g., the FE-207E, no longer in production, at 95 dB per watt input at 1 meter).

http://www.madisound.com/pdf/fostexdrivers/FE207E.pdf

Whether one will like drivers like this is, of course, a matter of taste -- and de gustibus non est disputandum.

DSC_5663 by mhardy6647, on Flickr

1) dang, that room looked better with far less junk in it.
2) in the interest of full and complete disclosure, at the time the photo was taken (last summer), these FE-207Es were being powered by a push-pull EL84 amp (Dynaco SCA-35).