Mesa Rectoverb Adjustable Bias Mod Question

[IzzyB]

I'd like to mod my Rectoverb from fixed to adjustable bias. Mesa won't provide the schematic for amps in production but I did find a posting for the Solo 50/Recto Series I on free society:
www.freeinfosociety.com/electronics/schempage.php?cat=1

I know they change board layouts all the time in amps. My rectoverb circuit board is not exactly user friendly. I believe I found the resistor in the bias supply. Its a 22K resister (red red brown orange) at the bottom of the board under the right corner of the 30uf filter cap. The schematic for the bias supply shows three resistors in series: 68K, 22K and 33K but my circuit board only has the 22k resistor in place. The 22K resistor leads to a 1k resistor then goes across the bottom of the board to a white 220 ohm resistor before it goes on to a series of rectofiers and gets lost.

Questions:
1) is that 22K resistor the right one to mod?
2) what do you think of a 15k resistor in series with a 15K pot?
3) Or maybe a higher value pot?

Thanks for the help.

[stokes]

http://www.tubefreak.com/mk2pwr.gif Check this link.It is a MKII power supply that shows the bias supply.In my experience most Mesa amps I've seen are similar.This one shows a bias pot,which I have never seen in any Mesa I've worked on,but that shows how you would put a pot in there.Just replace the fixed resistor that is in your amp in that position.If you are replacing a 22k resistor,I would use a 50k pot.I dont use the fixed resistor in series as you describe,just make sure the pot is set in the middle before you install it.I like to use multi-turn cermet pots,they stand up to the dc voltage better than a standard volume type pot.The multi-turn feature makes it easier to dial in.Always use a pot of twice the value of the resistor you are replacing,that way you have a fairly wide latitude to dial in for different tubes.