Biasing/whammy tuning effect link?..

[Sam Laming]

I've finally just biased my Herbert pretty perfectly/accurately but I noticed something; I'd get seemingly all the pairs perfectly within 0.5 of 60ma, then go back to the first one and check it and it would be miles out this distance shortened until I got it pretty perfect after doing it multiple times but is this like the whammy bar tuning effect - you tune one string and it pulls up on the others so you have to just keep tuning them all till it's good?

Done now though I can't imagine having an amp without external bias pots now

 

[steve_k]

I've finally just biased my Herbert pretty perfectly/accurately but I noticed something; I'd get seemingly all the pairs perfectly within 0.5 of 60ma, then go back to the first one and check it and it would be miles out this distance shortened until I got it pretty perfect after doing it multiple times but is this like the whammy bar tuning effect - you tune one string and it pulls up on the others so you have to just keep tuning them all till it's good?

Done now though I can't imagine having an amp without external bias pots now

Some of it will depend on the tube qualities. The bias trim pots are so sensitive that it can be a real trick. Power should be distributed evenly with the 3 pairs. I have found on the VH4 and my Ubershcall which have only one bias trim for the quad that the last tube in line gets the least current and getting all 4 dialed in exactly ain't gonna happen. Plus/minus 10% of your target is acceptable.

Steve