Tube types for a randall LB50 head

[Keven]

Hey guys,

according to the manual, the Randall LB50 is supposed to be self biased and it says i can use a variety of tubes to my liking.

so far i tried mesa branded 6V6, redplate... jj 6v6, redplate. WingedC EL34, redplate...

it seems odd that so many tubes will redplate.

it comes stock with JJ E34L. i'm going to buy another pair and see if they redplate. the current ones don't redplate at all!

I'm not with the amp at the moment but i do plan on using my bias-rite to check the plate voltage and see what happens.

here's the manual:

http://www.randallamplifiers.com/images/stories/manuals/LB50C-LB50H-LB112MANUAL.pdf

also, what preamp tubes would be decent these days? haven't had much experience with these so far. budget isn't really a limit.

thanks guys!

[jpfamps]

By self-bias, I assume the amp is cathode bias.

This would be optimistic to get 50W from a pair of EL34s in this configuration.

The E34L biases similar to a 6L6, so I would expect the cathode resistor used would work for 6L6s as well.

Genuine EL34s would probably require a larger cathode resistor to bias correctly, and hence the red plating.

6V6s have lower dissipation rating than El34s, and as I expect the plate voltage is way over spec for a 6V6, this may account for red plating with these valves.

[Keven]

So according to you i could safely replace the E34L's with 6L6GC. that's good to know!

[jpfamps]

So according to you i could safely replace the E34L's with 6L6GC. that's good to know!

Yes, that substitution should work.