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In Reply to: Gordon Rankin: "2a3's..what a waste of time"...So what you're really saying is... posted by Iczerman on March 1, 2007 at 15:07:50:
When trying to do the imposible, ie compare tubes, I suggest that there has to be a speaker / amplifier pairing. A 45SE into 100db easy load speakers in a large room just won't cut it, no matter how good the "quality" is. 110db yes, or 300B with 100db in a mid to large room. Maybe you get my drift. To describe any tube as simply better than an other is ok in theory but in practice this is just a single component in a system.
Follow Ups:
It's VERY difficult to do a comparison without other confounding factors, as many have pointed out here.The closest I have come is to compare a 2A3 and 300B in the same amp, at the same operating point. These two tubes have very similar transconductance and gain, so in this amp they put out the same power, have the same damping factor, etc - removing those factors at least.
Using this amp some years ago I have compared carefully the Chinese biplate 2A3 with the Svetlana 300B. I've also presented this comparison to two other audiophiles in their systems. None of these comparisons were double-blind. We all preferred the 2A3. Driver was a 6J5 with current source load, running about 250v on the plate - in other words, more than 6dB of driver headroom and a quite linear driver circuit.
I also conducted a "tube tasting" at one of the early VSAC conferences (blind comparisons but not double-blind) among several different 300Bs, using these same amps and with about 20 listeners. I would say that the difference between the 300Bs was about the same magnitude as the difference between the Chinese 2A3 vs. the Svetlana 300B.
I'm handicapped in these comparisons, as I only have old stock 2AE3's, and no new ones that are half/heater 300B's. However, I have heard most of the current commercially available 300B amps w/ WE 300B tubes, and I own 2A3's, although it's not a winner/loser choice- both are excellent and it's what flavor one prefers. I can see Gordon's point as a mfr. having to rely on current prod'n tubes, but fortunately hobbyists successful in our paying professions aren't limited in this manner. I have 6 nice old 45's 'aging' in the basement, will test them out sometime....need impetus, though.
Hello Paul.
can you share the 6J5 ~2A3 circuit ?
I'm interested in building it . what is the OPT you was using ?
Thanks
LT
The original version was published in the old VALVE magazine/newsletter under the title "SEX and the single 300B" (because it was a rebuild of the original S.E.X. amp, long discontinued). It's in the November 1997 issue, with several mods documented in later issues. All this was long before I started doing designs for Bottlehead.The original circuit used a 6SN7 in mu follower, set up so that a 6SL7 could be substituted directly. For my ears, I quickly decided I preferred to take the drive from the lower plate rather than the upper cathode, and also that I preferred the 6SN7; it was later modified to use a current source, and the 6J5 substituted.
The power transformer, also discontinued many years ago, had two windings at 2.5v, 1.25A, which could be wired in series for 300B or parallel for 2A3.
The output tube ran at 325v and 55mA with a 1200 ohm cathode resistor, with a Magnequest TFA-204 output transformer of 3K primary impedance. Total power supply voltage was about 400v. This is a plate dissipation of 18 watts, exceeding the 2A3 rating of 15 watts. The Chinese 2A3s of 10 years ago had a reputation for being rugged but having relatively short-lived cathodes, and they were quite inexpensive, so I did not mind the thought of replacing them frequently - "smoke 'em if you got 'em"! I measured 6 watts at 10% THD at the onset of visible clipping on the scope.
This amp served me well for many years, but I don't think it's practical today because of the unavailable power transformer and the excess plate dissipation. It is a direct ancestor of the current Bottlehead Paramour. I'm happy to answer specific questions about that design here, but any detailed discussion probably belongs on the Bottlehead forum.
A friend, who posts here as "richardl", has built a variant of this design using the Magnequest PGP8.1 power transformer which produces even more voltage; he uses the Sovtek 2A3 which is pretty rugged. The current version uses a choke-modified mu follower, but we are working on a modification to a choke loaded driver with separate voltage regulation.
Hi Paul.
is your one the same circuit as Les he posted below ?
http://gallery.AudioAsylum.com/cgi/gi.mpl?u=33876&f=se_glorya.jpgit also use half of the 6SN7 driver the 45 and I think it can driver the 2A3 no problem
Cheers
LT
No, not at all the same.
Paul.
I thought so too .
could you mind send me your circuit Via email .
Thanks
LT
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