Is anyone familiar with the process to bias the TRL Dude Preamp

I was saddened to learn that Paul Weitzel has passed away earlier this year. I was wondering as I was in the process of replacing tubes in my TRL Dude, it appears there is a potentiometer for what may be biasing
of one of the tubes. Is anyone familiar with this process and can share it here? I am not sure which tube
gets biased either, but it would appear to be one of the three power supply tubes. Thanks in advance.
Hi tellefsen. Contact me thru this Agon system and I can help you. Your high voltage power supply caps should be set to a particular voltage depending on the version of your Dude. The latest generation with the 1 Inch thick faceplate should have 325-335 Vdc on those power supply caps. The pot you are referring to allows you to adjust the Vdc to hit that range. 

I need to know the particular Dude you have to be sure of this setting. Changing your tubes should not throw the voltage out of range I'm most instances. 


I only checked when I replaced Sprague electrolytics for MR Clarity film caps, same procedure though.

I have a 2nd generation Dude (liked looks better, no big deal)

The pot actually sets voltage for the power supply section overall, not any particular tube bias.

The preamp should be FULLY WARM, for a steady meter read.

Set voltmeter for proper DC range.

Voltmeter RED probe/clip goes to first cap on right bank (POSITIVE +)

BLACK probe/clip to (STAR GROUND-) usually the last cap towards rear of preamp, you’ll see the wires bunched together.

Do this carefully and slowly, the voltages can be you-know-what.

If you don't feel safe or sure, have a tech do it.

We have not heard from the poster? Please let us know if you are all set as we are interested! 

Sorry for the slow response. I have been on travel. Thanks RX8MAN for the procedure.  Bill, I may still call you to talk through this. Mine has the 1inch face plate. I think it was built in 2010.
Great . 335 Vdc is your target. Nice preamp!
335VDC is where mine’s at, there will be a plus-minus 5 volt swing or so during your dial-in, that is normal, the trim pot is sensitive, as long as it’s in that range your good.
Sorry to hear of Paul Weitzel's passing. His equipment was not for the faint of heart (or back!)