More Headroom on Rocket - Plate Bias Resistor?

[davidskywalker]

This may seem a bit basic, but I'm looking to get the best headroom on my new Rocket build. I know that if I use the 280V instead of the 250V I'll get more headroom, but I've been informed to change the plate bias resistor. However, I did notice on Ceriatone's Rocket layout there is a voltage switch to go back and forth. Can you guys shed some light on this or point to a good post on this?

[M Fowler]

Change the 220k plate resistor of V1 to 150k or 180k and can increase voltage to V1 as well by lowering the dropping string resistor from the filter cap.

Using a switch you can switch between 250 or 280 HT leads but it really isn't worth it in my experience I like the higher plate voltage. I've ran JJ el84's without problems on the stock Rocket bias resistor with the 280-0-280 HT.

[Mark]

Perhaps at the input to the PI (after the 220K resistor) you could put a 220K to earth thus forming a volume divider. This would allow you to still get the same compression from the cathode follower whilst having a smaller signal getting amplified by the P.I. stage.