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Old 4th December 2012, 02:55 PM   #11
cotdt is offline cotdt  United States
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The older RCA 2A3's were single-plates, basically a smaller 300B. The single-plate RCAs go for a ridiculous sum of money at the popular auction sites. I don't know why 2A3 eventually became dual-plates, like two parallel 45s, as it is a strange design. Making modern production 2A3's single plate is a good design decision IMHO.

That JJ 2A3-40 I have, is really a 300B plate. It sounds just like my 45's, except it gobbles up 2.7A of current for its filament.

You can operate a 45 (12W dissipation) at 2A3 levels and get the same power, which renders the 2A3 pointless. 5W at 5% distortion has been measured with the 45. If you don't need your tubes to last many years, this is the way to go.
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Old 4th December 2012, 04:43 PM   #12
kevinkr is offline kevinkr  United States
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The JJ 2A3-40 is a good tube last time I checked.

Kenrad 2A3 box plates from the late 1940s are excellent IMVLE. I've had a few pairs in SE amps over the years, current owner of said amp likes the Kenrads a lot.
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Old 4th December 2012, 06:14 PM   #13
jlsem is offline jlsem  United States
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The salient feature of the original, low-distortion RCA 2A3 was the harp filament. No new production 2A3 has it.

John
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Old 4th December 2012, 07:05 PM   #14
Cassiel is offline Cassiel  Libya
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Quote:
Originally Posted by kmaier View Post
In any case, I've not seen or heard anything magical about the RCA 2A3 tubes (dual-section types).
Yeah, too much hype. Not a bad tube but nothing to go crazy over.
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Old 4th December 2012, 07:06 PM   #15
tinitus is offline tinitus  Europe
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price is not far from Emissionlab EML2A3

anyway, why is it cheaper than its 300B brother

UPS ! that one in the pic is a much cheaper Shuguang with Psvane logo :scatch:
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Old 4th December 2012, 10:28 PM   #16
freax is offline freax  Australia
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maybe i should go into buisness for myself, a harp filament doesnt seem too difficult to manufacture.

I can call my company "I'm so vain"
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Old 4th December 2012, 11:39 PM   #17
kmaier is offline kmaier  United States
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Quote:
Originally Posted by cotdt View Post
The older RCA 2A3's were single-plates, basically a smaller 300B. The single-plate RCAs go for a ridiculous sum of money at the popular auction sites. I don't know why 2A3 eventually became dual-plates, like two parallel 45s, as it is a strange design. Making modern production 2A3's single plate is a good design decision IMHO.

That JJ 2A3-40 I have, is really a 300B plate. It sounds just like my 45's, except it gobbles up 2.7A of current for its filament.

You can operate a 45 (12W dissipation) at 2A3 levels and get the same power, which renders the 2A3 pointless. 5W at 5% distortion has been measured with the 45. If you don't need your tubes to last many years, this is the way to go.

Yes, single-plate 2A3 tubes go for large sums these days. Being a true single triode, it should have an edge over a dual-plate version (which is two triodes in parallel). The latter was created as it was cheaper and faster to manufacture (and with better yield most likely). Take a close look at the filament structure in the original single-plate version and it becomes obvious. Also note that the single-plate is more fragile and can not handle any real additional plate dissipation over the 15-watt spec, while a good robust made dual-section type can run at 18 watts and not see any red.

As for a 45 replacing a 2A3, it doesn't... you can push it (the 45) to around 11 watts dissipation with good airflow, but you won't likely get more than 2.5-watts (class A1) from it. I've yet to see any A1 operating point that gets 5-watts from a 45... care to share? Besides, why purposely trash a nice triode for a few dB at most? I certainly wouldn't recommend it. That being said, I do run mine around 10-watts dissipation (~300 volts @ 34ma) and get ~2.25watts output. Note that 300 volts and 10 watts is an uprated spec which was later published with ST glass versions.

Regards, KM
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Old 5th December 2012, 07:14 AM   #18
tinitus is offline tinitus  Europe
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a few years ago, wasn't there also introduced a fine expencive 2A3 tube running on 6.3V filament ?

would that be other than a 'changed' 6A3 ?
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Old 5th December 2012, 04:29 PM   #19
kmaier is offline kmaier  United States
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Quote:
Originally Posted by tinitus View Post
a few years ago, wasn't there also introduced a fine expencive 2A3 tube running on 6.3V filament ?

would that be other than a 'changed' 6A3 ?
Can't vouch for new production, many of which are called one type but really have nothing in common beyond the type number. There is a 6A3 and also the 6B4G (same as a 6A3 with an octal base). Then there's the 45 Special, which is a larger single plate triode (more of a 2A3 size) with a 6.3 volt filament. Some swear that they are truly special, but I've not had a pair to play with, so I can't comment.

One note of interest, the 6B4G is typically implemented the same as a dual plate 2A3 grid/anode/filament structure. The difference is in the filament, where the 2A3 has both filaments wired in parallel, the 6B4G has them wired in series. This is significant change... I have but one pair of 6B4G tubes where they are wired in parallel, Raytheon, true dual (separate) triodes and true parallel operation. In short, an AC filament supply won't work very well with the 6B4G series-wired filaments.

Regards, KM
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Old 5th December 2012, 10:02 PM   #20
cotdt is offline cotdt  United States
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Psvane's entry level 2A3's look to have solid construction. Worth a try for the price. The Shuguang 2A3B look solid, too, and pretty cheap. I don't know if the Psvane and the Shuguang are the same or not.
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