Originally Posted by mintchris
I replaced the 6j1's with GE 5654w's and they were a nice improvement.
I am going to pick up a quad of Mullards soon to see what that does.
Only thing is I have never biased an amp before. Is it a pain to do?
Biasing the MS-20L is easy. Get a multimeter and use the millivolt range so 0.4V will read as 400 on the scale.
Make sure the amp is good and warmed up (I usually wait until it has been on 20 minutes).
Turn the volume all the way down.
Make sure the - and + leads are connected to the meter properly.
Put the - and + leads in their respective places for one of the output tubes.
If the reading is not 400mV (milli Volts), using the supplied tool SLOWLY adjust the potentiometer (clockwise to increase, counterclockwise to decrease)
Repeat for each output tube then do a repeat check on each tube before you call it quits.
Using the millivolt range the reading will jump around a little, not to worry.
When you put different replacement tubes in the bias may be off by quite a bit, if so take your time. For example when I went from 6P3S-E to EL34eh the bias was at 175mV. I raised each tube 50mV at a time until all were at 400.
Have fun and enjoy the music.