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In Reply to: RE: Mullard XF1s vs EH 6CA7s posted by FenderLover on September 05, 2016 at 10:20:43
Steve
I have every Mullard EL34 made from XF1s to XF2s,both single and dual getter,I have Amperex square DD getter and the metal based Philips.
Maybe this quad of EHs I have are exceptional because I did not get this sound with my first quad of EHs which tested in the low 7000 range.
When you did your test,were you doing it in a guitar amp or a hifi amp? That changes the perspective entirely. These particular EHs have a very warm and full bodied midrange and I didn't have this with my other EH 6CA7s.
This is why I say the test results may be key in this case..
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Follow Ups:
it happened to me too with a quad of 6ca7 eh factory tested :
gm> 8500
lp> 63
The price was the same ,the quality astounding.
I think could happen with other lucky selected quad by other brands
(i had a rft el34 tfk marked that sounded ....just perfect!
on the contrary i have a Ge 6ca7 quad measured on Sophia equipment
which lasted 3 months and blew my fuse away....there is an "alea "
with tubes i found mirrors aspects of life...it is important
to have skills ,but luck or fate has great impact on what is going on)
I have never heard these tubes described as warm, or full-bodied midrange. In either guitar or hi-fi amps. At least ones designed to take the EL34 as OEM. You didn't change any coupling caps or idle settings in the gain stages? Idle bias dissipation the usual 6CA7 range?
What vintage are those EH 6CA7 tubes? Be nice to pick up a few sets of them.
Steve
I did do the typical McShane rebuild with all the upgrades of the common point ground,820uf caps in the doubler,Teflon coupling and decoupling caps,
Schotkys in the doubler and added choke. Both tubes ran in the same amp.Maybe Jim can explain more why these higher GM testing EHs sound so good.
Maybe mine are exceptional because I have written about these tubes about five times now. You have known me long enough to know that when I keep posting about the same things,I'm pretty excited about it.This is how I was with the K40ys and the 6P3SE tubes..I only put teflons in this amp because I feel they add some sparkle to the more dull sounding EL34s I have tried which is most of them.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 09/12/16
I don't have any EH 6CA7 or 6L6GC on hand at the moment. Is there a code to read manufacturing date, like in Svetlana (St Petersburg) tubes?
Thanks!
Yes, there is a four digit date code. The first two numbers are the year, the last two are the month.
The quad of mine are 02 07 gm 8500 Ip 63
That's July of 2002. But don't put a lot of faith in the "matching" numbers. The "factory" or "distributor" match is not so hot. Also realize Ip stands for plate current - yet when adjusting the bias the VAST majority of audio (and many guitar) amps read CATHODE current via a resistor between the tube cathode and ground. When I match tubes I match using CATHODE current since that's how I and most other audio guys measure the bias current in our amps.
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