Wondering how bias is adjusted on these amps...is there a bias pot inside the amp, as well? I ask because a few years back I had my Super Reverb serviced and they re-wired the hum balance control to be bias adjust like the older amps, instead. If there is another pot inside that was formerly for bias, was it most likely bypassed altogether? Otherwise re-purposed somehow? Just wondering out loud. I can't open it up and look at the moment.