2A3 v 6550

[rick57]

I was thinking of doing a PP (Sovtek) 2A3.

Then I started seeing the odd post by SY and Frank about the 6550 variants being better value.

Who knows - does the 6550 triode mode sound as good as the 2A3?

(A 6550 PP will produce more power, which may be a plus): are other considerations?

Which 6550s sound best?

 

[SY]

Frank and I are both fond of the old Tung Sol 6550s. They'll do great, if you can find them.

I have no experience with current production 6550.

 

[rick57]

Thanks Oh man of many faces.
Who’s had the pleasure of listening to both new 2A3s and new 6550s in triode mode?

 

[rick57]

SY you probably know . .

"The legendary Tung-Sol 6550 is again available.
Manufactured in Russia to the original specifications, and after years of development, an expert team of vacuum tube designers has re-created the best series of this famous tube type that has ever been marketed.
Initial stocks have arrived and can be supplied for $A72 each (inc. GST) plus $2 matching per tube"

http://www.evatco.com.au/new.htm

As good as old?

 

[SY]

I haven't tried them, but I seriously doubt it. I'd be interested to know if anyone who has used the genuine Tung Sols has actually tried them, though.

 

[rick57]

(Not having heard either) couldn’t a contemporary better paid Russian worker do at least as well as an underpaid comrade from the old era?

Why doubt the new Russia so?

 

[SY]

The materials once used in tube manufacture are, by and large, just not available anymore, no matter how good a worker Sasha is.

The large scale manufacturing setup which cost-justifies proper production tooling just doesn't exist- these tubes are now niche items, not mass-produced. The variation inherent in artisinal manufacture can be interesting if you're talking about wine or bread but not so if you're dealing with tubes.

Every copy I've tried of "classic" tubes has been notably inferior to the original. Some of the copies are nice tubes, but...

So... I can't honestly say that the new 6550s aren't as good as the old ones, not having actually tried them, but it's where I'd lay my bet. I'd love to be wrong about this one- I'm now totally out of Tung Sols.

 

[kmtang]

2A3 - excellent

I have built 300B, 2A3, and 45 SE power amps. 2A3 sounds most smooth and sweet.

I believe 2A3 should be great even in PP configuration.


Johnny

 

[rick57]

There seems to be a distinct Class System in the tube world:

- 300B, 2A3, and 45 – the upper class
- the rest

Does this reflect sonic reality; for the price paid?

 

[SY]

That's a pretty limited universe of good tubes, more reflecting fashion and familiarity than engineering reality. I don't know much about "class" in the sense you're using it, but there are a LOT of tubes out there which can make first-rate amplifiers.

 

[rick57]

In the almost absence of original Tung-Sol 6550s, and eliminating 300Bs & 2A3s on price, could you suggest to a new newbie (though I just ordered two books – Morgan Jones a one by a Dutch author)
- a handful of good options (triode/ pentode that can be used as triode)that would be good choices

Thanks

 

[audiousername]

If you're considering 2A3 pp but are concerned about the price, you might consider using EL36/6CM5 or heater variants thereof. The curves are a reasonable analogue to the 2A3 (µ=5, r_a=740 ohm)

Another option might be triode-strapped GU-50 (a Russian transmitting tetrode), it has rather nice curves, and 40W P_a.

 

[SY]

Rick, I'd think strongly about paralleled EL84. I'm experimenting with the JJ tubes and am very happy with them. And low B+ requirements compared to many other tubes.

Exotics? The 6528. Tough to bias, tough to drive, a hog of a heater, needs lots of air, but stunningly low plate resistance and high transconductance. No funky package/socket like those big Russian jobs. A little searching will turn these up at pretty reasonable prices.

There are some "6BG6" floating around that are really rebased 7027. If you see any, they do very well triode strapped with 6600 ohm p-p.

 

[planet10]

think strongly about paralleled EL84

Even just one in an RH84 style amp -- more power than a 2A3 and quite good. Class A PP is a bit harder to get right, but should make an even better amp.

dave

 

[PRR]

> Why doubt the new Russia so?

SY is comparing to TungSol. Classic USA tube making was very sophisticated: it supported a significant special-metal market and RCA GE et al knew a LOT about tubes: how to make them very good (and how to make them very cheap if that's what was wanted).

TungSol was started JUST to make Big tubes BETTER than the best from the Big Brands. The early TungSols are amazingly good tubes. And they did find a niche as electronics expanded through the 1950s.

The "new good" 6550 has been tried by organ players and apparently stands up well in Leslie amps which work their 6550s pretty hard. The Hammond has a simple tone structure, so any great change in 6550 sound would be noticed. The Leslie works the 6550 hard, but not to its voltage limits; how it will hold up in high-volt uses, I dunno.

I think a triode-strapped 6550 makes a great SET. I have not heard a 2A3 since they were common in old radios (they were not that common then) so I can't say if a hot-filament sounds better than a unipotential cathode. Considering the price difference, the fact that 80% of the amp can stay the same for 2A3 or 6550, and the fact that you have to ask, I say try 6550 but leave room to have a 2.5V filament supply and old-style socket.

When you get into P-P, I think many of the difference cancel. Quite bent tubes can make fine P-P amps.

As Jason says, the 2A3 is such a perfect triode that it was cloned over and over again, usually with heater-cathode because that is so much easier and nobody saw a problem with that until the 1990s. Several TV V-Sweep tubes are pretty-near a 2A3 plus a small volt-amp triode. 6EM7 is a 10 watt 2A3-ish big triode plus a Mu=60 triode much like 12AT7. Two of these could make a fine P-P amp at the several-watt level. 6EM7 and similar TV V-sweep tubes are mostly so darn cheap that you could use four and get enough triodes to have many-watt PPP plus fancy driver. (Take the B+ up to the tube rating. Adjust load impedance tangent to the Pd line at B+ to get the most power within the plate dissipation rating. This also maximizes damping. You can take a little more power by lowering load impedance and allowing the load-line to rise a bit above the Pd line: this is not fatal for speech/music duty.)

 

[rick57]

Thanks for all the ideas,
I’m now researching them futher. (And waiting on two books, won’t be overnight . . ).
Slightly leaning to a PP EL84,

maybe with a switch to select triode/ ultra-linear/ or pentode, depending what speakers they’re hooked up to. But guess this means the trannies need to be optimised for one mode?

BTW, what are the main derivatives/equivalents of the 807?

 

[Sheldon]

Thanks for all the ideas,
I’m now researching them futher. (And waiting on two books, won’t be overnight . . ).
Slightly leaning to a PP EL84,

maybe with a switch to select triode/ ultra-linear/ or pentode, depending what speakers they’re hooked up to. But guess this means the trannies need to be optimised for one mode?

BTW, what are the main derivatives/equivalents of the 807?

Lots of EL84 schematics available. Here's a couple: http://www.electra-print.com/images/PSA_EL84.pdf
http://www.wdehaan.demon.nl/mono/mono/el84dc.html
or this:

http://www.diyaudio.com/forums/showthread.php?postid=552739#post552739

No need for mode optimized tran. Just need UL taps.

Sheldon

 

[SY]

807 is a lot like 6L6. It's even closer to 1625.

 

[rick57]

Sheldon

Thanks for the links

> No need for mode optimized tran. Just need UL taps.

Cool!


What do people think of variable NFB - a gimmick or useful?

 

[kmtang]

You can get a pair of NOS RCA 2A3 at around US$150. I believe this is still reasonable. If you want new ones, Electro Harmonix Gold Grid 2A3 is not a bad choice with good pricing.

2A3 is still the best to me.

Happy listening.

Johnny