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Old 4th September 2004, 08:18 PM   #1
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Default Best 6CA7?

Hey guys,

I was just curious what might be the best 6CA7/EL34 tubes available in terms of power handling capabilities? I've got an amp where I run the plates at 700v and the screens a bit over 400v; one channel uses a matched pair of later RCAs manufactured in Gt. Britain and the other channel matched NEC's. The RCAs can really take a beating but I have to watch the plates of the NECs to keep things from getting out of hand.

What do you guys think?
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Old 5th September 2004, 08:29 AM   #2
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Wink 6CA7 or EL34

Greets cadman,

From what I know, the 6CA7 and EL34 (patent issues) are really two different critters, though very similiar. Running at 700V Vbb the really only choice are 6CA7's (NOS GE's etc.), maybe the EI BIG Bottle 6CA7's. If I'm not mistaken the JJ E34L can handle at least 600V maybe more, with a 15% increase in output power compaired to an EL34. At 700V you're really pushing it!
So knowing this (mmmm maybe), I would suggest the EI's with a conservative bias of about 25-30mA @ no signal and an OPT of around 6600 ohms or higher (haven't done the math).

Quote:
The RCAs can really take a beating but I have to watch the plates of the NECs to keep things from getting out of hand.
Yeah the Japanese (NEC) you are speaking of IIRC are really EL34's and they more than likely can't handle 800Vp let alone 700V without glowing cherry red or self destructing, and the RCAs may be true 6CA7's (Beam Tetrodes) or Mullard EL34's, don't know! Where as the NEC's are more than likely true pentodes (EL34's).

You see the original 6CA7's were built to handle 800Vp, but the EL34's much less, especially those continental slimmies that came out in the 70's and 80's! @ 700Vp you should be able to grab your speakers by the balls and make your ears reeally happy!

Hope the helps and good luck!
fdegrove could be of great help here, Frank?

Cheers
Wayne
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Old 5th September 2004, 09:03 PM   #3
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Hi,

Quote:
Yeah the Japanese (NEC) you are speaking of IIRC are really EL34's and they more than likely can't handle 800Vp let alone 700V without glowing cherry red or self destructing, and the RCAs may be true 6CA7's (Beam Tetrodes) or Mullard EL34's, don't know! Where as the NEC's are more than likely true pentodes (EL34's).
It's the other way around really...

As for the British made RCAs...Never heard about RCA having valves made in Britain for them but you never know.
These are probably true EL34s, they wouldn't withstand the 700V + anode voltage if they weren't.
I assume you're running them in class AB1?

Here's a link with more data on both types:

TDSL

Cheers,
__________________
Frank
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Old 8th September 2004, 03:16 AM   #4
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Thanks guys-

Maybe the RCA's are EL34s in disguise? Both the NECs and RCAs have the tall/skinny look and are labeled 6AC7, but you know the numbers game, especially in the early 70s (which I'd wager these are from). I guess I'll keep my eye on the 'bay to see what pops up, I'm quite happy with the Gt. Britain RCAs, and no sparking
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Old 8th September 2004, 03:29 AM   #5
jlsem is offline jlsem  United States
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Quote:
As for the British made RCAs...Never heard about RCA having valves made in Britain for them but you never know.
Late in RCA's tube-marketing life, they sold lots of British- (Mullard-) made tubes. I've seen 12AX7's, EL34's, E55L's, different triode-pentodes, and others marked RCA made in Gt. Britain.

John
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