Bogner Bias for XTC 101B


New member
Does anyone happen to know what the factory bias recommendations are for a 101B XTC? I know you can measure plate voltage and calculate it, but having owned a Shiva previously and biasing it, I know that there is usually some drift and that having been said Bogner usually has the factory bias nailed down to a particular value. For a Shiva, it was a bit lower than I would set up a Marshall for any given tube type. Wanted to see if that might be the same for an XTC.

The reason I am asking is I've noticed when pushed, my XTC gets a slight chorusing effect on it at higher volumes. Having worked on amps, built amps that's usually the sound you get when the tubes are biased hot and start to red plate.

I had the same chorusing effect on my Shiva when I had it and was able to get rid of it by adjusting the bias down. Interestingly enough with Bogners, while I've seen them sound like they might redplate, neither actually does. Which is good. Most Marshall's aren't that forgiving.


Well-known member
101B has plate voltages well north of 500V, more in the 525V range. You’d want to bias them conservatively in class AB. If using class A be sure your wall voltage is close to 115V or else you’ll run the risk of redplating.


I always kept mine around 31-32, but recently lowered to 27-28. The change is subtle but hearable, the tone became a bit less compressed, thus a bit more open. Seems like tubes have more "breathe" with that setting. Same impression while lower a bias a bit in my other amps (Engl Invader, Marshall JVM).

Regards, Andy


New member
One other quick question. When you use your mix knob when in parallel mode for the loop, should it function such that tired all the way CCW is dry and all the way CW is wet? Reason I as is mine is not that way, in the center it is loudest and dry, moving CW it adds in the effects but volume drops as you go full CW. I use series but I found that odd. Been like that since I got it.


Well-known member
Regarding the bias: I seem to recall sending an email to Bogner hq about this when I got my first 101b and saw what the plate voltage was. Pretty sure they told me 28ma.
Given the 525v-540v on the plates, I would recommend as cold as you can get without killing the tone. I think these amps sound better biased around 55% -60%.