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In Reply to: RE: 6sn7 GTA or GTB ??? posted by JimL on October 20, 2009 at 17:02:31
Thank you .I assume then,that if used in mono amps it wouldn't matter if one amp used a GTA and the other used a GTB
Assuming same manufacturer, identical construction and date codes it should be fine.
Actually, NO.
The GTA and GTB from the same manufacturer will sound completely different, in fact, in virtually every case, a GTB is a distinctly inferior tube sonically. One of the worst, actually.
I wonder why that would be considering that the only difference should be the design of the heater core. Maybe you're listening to tubes with different construction or significantly different date codes - remember I specifically mentioned identical construction and date codes. Certainly, tubes that are a decade or two apart in dates may sound significantly different.
Since the design of the heater core is different, it is of course not possible that a GTA could be the "identical construction" to a GTB, nor is is possible to have the exact same batch codes (date maybe).
The only exception to this is the tall bottle late 50's/early 60's Tungsol, where the GTB is exactly the same as the identical looking WGT - that is becuase they ARE actually the same. On these, you will see identical batch and date codes on top of the bottle showing they actually were both from the same batch.
With the exception of that particular variant of Tungsol, GTB's virtually ALL sound much inferior to a similarly dated GTA from the same manufacturer, whether that be RCA, Sylvania, GE, Westinghouse or otherwise.
What I meant by identical construction is same plate structure, etc. Of oourse the heater wire is going be be different but that isn't visible. It's certainly possible for everything EXCEPT the heater core to be constructed the same, same materials, etc. I'm not questioning your subjective results, and I haven't actually done extensive listening tests on GTAs and GTBs, I'm just saying that I can't see why if the cathode, grid and plate structures are the same, the materials are the same (which is why I said identical structures and date codes), why the sound shouldn't be the same. I can't imagine manufacturers back in the 1940s, 50s and 60s altering anything other than the heater core when going between GTA and GTB - just seems like too much of a hassle, especially since nobody was focussing on audible changes back then. The simplest way to make a manufacturing change is to do the minimum possible. Still, as I say, I'm going from a theoretical perspective and if you hear differences I won't disagree with that.
Which brand is your preferred GTA
Well, the very early Sylvania GTA - early 50's - with REAL chrome domes. but be careful here - for awhile, dubious or unknowledgeable sellers have been calling any and every Sylvania a with a top getter 'chrome dome' to try to peg inferior sounding tubes with the sonic reputation of the real thing.
The early 50's GE is pretty good.
If you can ever find a Canadian Westinghouse GTA from the mid 50's - those are outstanding. But hard to find.
1950's RCA are not bad. Not the greatest, but certainly far better than any GTB (except those Tungsols I mentioned earlier).
Would this be your preference for 6sn7 tubes if they were used in a preamp or a power amp
My preference is always a pre-1955 (or so) 6SN7GT. My personal preferences are the National Union black glass (early 50's), the KenRad 1945 black glass (or same dated clear glass version which is virtually identical in sound), the RCA early to mid 40's grey glass (commonly seen labelled VT-231 for military and 6SN7GT commercially), the bad boy 1952 Sylvania 6SN7GT, and the early to mid 50's Tungsol 6SN7GT which may or may not have round side mica spacers, rectangular side mica spacers or no side spacers at all.
After those, I love the 1943 to 1946 Raytheon 6SN7GT/VT-231 variants, as well as Hytron early 50's 6SN7GT and late 50's Raytheon 6SN7WGT, among others.
I'm not too fond of British 6SN7's like the Brimar CV1988, these I find a bit too rigid sounding, and there is no good Euro 6SN7. I've been through CV181's and B65's long ago and all the above I favor heavily.
Thank you for the comprehensive list.Unfortunately
6sn7GT tubes do not have the Voltage my amps need.So they must be GTA or GTB.
I don't know of any amp that requires a 6SN7GTA or GTB, that seems to me to be a poor design if in fact an amp runs the 6SN7 to the 450v range instead of typical 300v range. Puts you at a serious sonic disadvantage also.
To elaborate on astralnavigator's point, the real Sylvania "chrome domes" have the getter extending about 1/2 way down the straight sides of the glass, whereas the later Sylvanias have a top getter that only covers the domed part of the glass envelope.
Nice balanced bass and midrange response. Good clean high notes. Be sure to get them tested first, for noise especially. Hard to find good NOS 6SN7 these days.
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