Hi I have an old simms watt 100 watt guitar head, not the pa version. I have just got my hands on a bias probe and have had a quick look at the amp.
I am getting a reading of 74mV from the Groove Tubes probe which seemed really high and that is as low as the bias pots will let me go. I am using EL34s but I am not sure if the amp has been modded to run something else.
Also the amp only has one of the three preamp valves inplace, should theese all be ecc83s and is this likely to affect my readings for the power amp section?
I am new to servicing valve amps but I have sorted my 50 Watt plexi and this is my next challenge. Many thanks in advance for your replies.
Cheers,
Ross