trinityamps.com

Powered up my Triwatt build for the first time this evening and got ahead of myself - played through it for about 15 minutes before I figured I should check the bias (the amp sounds fantastic and I could've played longer).

So, with amp connected to the cab, master volume at 0, bias trim pot fully counter-clockwise and amp powered on, I took a measurement at the test points and got a reading of 13mV. Deciding I wanted to set it in the 19-20mV range, I began adjusting the bias trim pot clockwise however, the reading did not change from 13mV regardless how much adjusting I did with the trim pot.

Not sure what's going on here - either I've got a problem with the multimeter itself (not out of the question), or I made a mistake wiring the trim pot, or the trim pot is not working.

Any ideas?

Post a picture of the power supply section, specifically the area around the bias pot.

_________________
http://pdfelectronics.com

I had the wire from the 47K resistor on the turret board connected to lug #3 on the trim pot which in turn was jumper to (middle) lug #2 on that pot (lug #1 is wired to ground) - so lugs 2 & 3 are shorted together as per the schematic and layout diagrams. However, it would appear that the jumper from lug 2 to 3 wasn't making a decent connection - I simply moved the wire to the 47K resistor on the turret from lug 3 to the middle lug (2) and all is well now. Set the bias to 20mV.

In this instance, I don't think it actually matters if lug #3 is actually connected to anything but I re-soldered the short jumper between 2 and 3 again.

My Triwatt has got a little hum to it when it's cranked - overdrive gets a little wild for noise beginning around 2 o'clock - not as much hum as my JCA20H but I may look into seeing if I can improve it anyway.