Express Tweaking....

[ampkits]

Hi!

Paul Ruby is here?!!

Hi Paul, how ya been! Been a while...

Salut!

Nik

Darn, this is good forum! Where have I been?

[hairyandy]

Hey Paul,

Any thoughts on changing an Express to cathode bias with EL34's? I'm wondering if it will get any of that "chime" that is associated with cathode biasing or possibly be a little darker. Either or both could be really cool with an Express I would think. BTW, Marta is still kicking a**. I've got a pair of old Philips/Mullard EL34s in her and it's pretty darn great.

If I were to change Marta to cathode bias what value resistors should I use for the cathode? I was reading the Weber "Tube Amp Talk" book yesterday which got me thinking about this. He is recommending "anywhere form 300 to 600 ohms at 20 watts" for a 6L6 amp which I would assume would work as well for EL34s? He also recommends changing the grid return resistors from 220K to 470K or 500K for EL34s.

Thanks for any insight or ideas,

Andy

[paulruby]

Try KT77 first. Then try KT66. This will take you in the direction of more chime and less break-up. Be prepared to tweak your bright caps in each case to keep it from getting too hot in the top end.

Cathode bias is going to steal away ~15V from power tube plate bias and that will tend to take away a little top end (but may sound smoother and be helpful if you switch to KT66).

(And... Hi Nik

[hairyandy]

Thanks for the reply Paul. I have tried a pair of JJ KT77s and they were OK but not quite what I wanted. They did seem to have more headroom which is cool for certain gigging situations where you might run out of gas. I wouldn't want to ruin your lovely work on this thing, I just was reading that book and got to thinking...sometimes that's dangerous!

Andy