Express and cathode bias... schematic!

[riscado]

Ok I've got most of my board populated with components, I'll be starting the cab as soon as possible and I'm waiting on the chassis... I will be using hammond transformers.

I wanted to do the amp as original, however it'll be too loud, so I decided to tame it a little bit (even though I'm not sure I'll even notice that much of a difference) and do it cathode biased, I made the changes directly in a copy of a francesca schematic, could you guys tell me what you think of it.

Thanks in advance

[rfgordon]

You'll need to decide which tube types to run, since in a cathode bias arrangement, the EL34 and 6V6 are going to want different values for a given B+ voltage. For a B+ of around 405, a shared 250 ohm would keep a pair of 6V6s (or 6L6s) happy, but it wouldn't be optimum for the EL34s. The EL34s would want a lower value. Of course, you could make it switchable.

You won't tame the volume much (my first TW Exp was cathode bias EL34s, and it was "blow your hair back" loud). However, the transition into power tube overdrive will be a bit different, and you might like the difference. I do, and it's why I build cathode bias amps.

[riscado]

the schematic I posted is setup for el34's only, however if I wanted to run 6V6's I guess a switch to remove one of the cathode resistor/cap pair would do the trick...

I though it would be very different volumes wise, I'm looking forward to spot the differences between the two bias types though.

thanks

[Matt72]

Cool idea! So what would a the proper values be for the EL34 bias resistors? And rated how many watts?