EL34's in a 5e8a twin

[Zer09]

I recently built a 5e8a head using an old organ amp chassis and transformers. The amp used a couple 5u4's, a pair of 6l6gb's and a ton of 12A-7 tubes on the organ's percussion unit. Filament current is not an issue, I've got a 13 amp tap and a separate 5 amp. The tranny is massive. I've built and played nothing but 6l6 and 6v6 amps ups to this point in my life and am now starting to play with el34's. I figure a tweed fender would be a good starting point to try them in a Marshall style circuit.

So I have the filament current supply and a Weber Coppercap GZ34 to replace my 5u4's.
My question is in regards to the primary impedance mismatch I will have and how does this effect sound, tube life, and OT life (since I'm using an OT that is 50 years old) Anything else I'm missing? Will a real GZ34 hold up in this circuit with EL34's? Everything I put in will be NOS Mullard and I'm a little nervous about toasting them.

[Diablo]

I have a Weber kit 5E8A that is running EL34s without any problems. It has a Heyboer OT with 4K primary impedance, which also works fine with 6L6 tubes. I have 1K-3Watt screen grid resistors for tube life. A real GZ34 or 5U4GB will work fine.
http://music-electronics-forum.com/t15066/

[Zer09]

Thanks Diablo. I'm going to try it tonight along with some 5881's. What do you think of the sound with the EL34's?

[Diablo]

The EL34s sound much better than 6L6s in the 5E8A. Yes, I know it's not what Leo intended, but they work very well for whatever reason. I never thought about pulling the EL34s out once I played it with them in.

[kg]

maybe during initial testing/burn in it would be a good idea to keep those mullards on the shelf and instead use some crap tubes?

red plates would be a shame...

[jmaf]

My 2 cents: Pay attention to pin 1 of the EL34's when assembling this idea. 6L6 based Fenders used it for a contact bridge for pin 4, so you'd end up with HT on the suppressor. Also increase the G2 resistor to 1k instead of 470R or it'll run very hot and smoke.

+1 on kg's suggestion to save the nos and test using a crap pair. I keep tubes removed from amps in a separate box for that purpose.

[Zer09]

I never got around to trying the EL34's last night because I tried 5881's and I loved them so when i put 6l6's back in that's what they'll be.

I have a 1 ohm bias resistor going 8-1 to a banana jack on the chassis then grounded for bias test points and did the 1k screen resistors when I built it. I was kinda expecting to try the EL34's when I realized how much filament current the pt could supply. I also have sets of used but strong JJ's of just about every variety that get subjected to the debugging and the first power on with tubes. I tend to keep them in for a while until I feel comfortable. Thanks guys.

On a similar topic, has anyone tried the JJ 6CA7's? Supposedly 6CA7's they can take up to 500v on the screens and I have another amp that puts about 395v on the screens from a second b+ rail that just causes the screens to glow bright orange. I believe the EL34 screens have a 425 volt limit and it's just too close for comfort. Though I may be better off using zeners to drop both rails down.