L
loganflynn294
Member
So I'm not new to biasing tubes but I've never swapped from EL34 to KT88 before and I'm having a weird problem. Amp in question is an Uberschall Rev 2 serial #220 that currently has EL34's in it biased at 36ma with 470v measured at pin 3 with the amp running (not in standby). One of the factory installed bias resistors has a resistor piggybacked on top that someone soldered in. It's a 5 band resistor, the bands are so close together that I can't tell if it's 100k or 130 ohms (brown, orange, black, black, brown). Anyways, popped in a matched set of Gold Lion KT88's and I cannot get the bias low enough. With the trim pot set to where the 34's biased at 36ma (almost all the way counterclockwise) I'm getting 120ma. If I turn the trim pot clockwise all the way the lowest it will go is 80ma. How can I get the bias lower? I thought if anything I wouldn't be able to get the current high enough not have it way too high. What am I missing?