Help needed with resistance calculation

[Che_Guitarra]

My next project is to build a 2061X 20W Marshall Lead & Bass amp - I plan to install a variable voltage regulator (VVR) over the power section and phase inverter.  Here's the schematic i'm basing the build on:

Here's the same schematic with VVR installed.  I'm happy it's OK, but if you can spot any errors i'm all ears.  I'm also hoping some brighter sparks than I can work out the new resistor values I need across the B+ rail to maintain correct voltage.  #2 and #3 might be OK, but i've highlighted them anyway:

Any input most appreciated.

 

[PRR]

Well, since you know the final answers (320V etc), you could just tack-up strings of 10K resistors and find those voltages by experiment. Put five 10K in series at resistor 1. Fire-up, you will probably find the "320V" pretty low. Short-out resistors 40K 30K 20K until you get near 320V. Install a permanent part of that value. Really cheaper than brain-work. And MUCH faster.

Resistors 3 and 2 stay the same-- they are doing the same thing as before.(*)

Resistor 1 is supposed to drop 385V-320v or 65V at 2mA (each half of V1 is drawing 0.96mA), so is nominally 32.5K. However V1 has the weakest signals and you are bypassing a lot of B+ filtering, so I'd split the 33K as two 15K-18K parts and hang another 20uFd-40uFd in the middle.

It seems very dubious that the cathode resistor under V2 is 8.2K. This will starve V2. True, a too-happy V2 will slam the EL84s into cutoff.... but you ought to find confirmation.

(*) Actually resistor 2 is carrying 2mA less since you have removed the V1 feed from it. It should be a little higher. I suspect it makes little difference, and that you can cut-and-try its value quickly.

 

[Che_Guitarra]

Thanks for the tips PRR - it's much appreciated