What controls the voltage here... (pic inside)

[JubileeMan 2555]

I'm continuing to mess with a friend's super reverb and when measuring voltages I noticed something funny. At this location at the Bias resistor 2 of my amps (his and another fender of mine) measure about 93v and my super reverb measures 104v.

Then I looked at schematics. THe OLD schematics for super reverbs show it should be 104v, and the modern super reverb reissue schematic shows 93v ??

Does this voltage not really matter so that it can have a big range? What controls this voltage?

ANy help would be great!

http://www.shelleygrund.com/images/biasresistor.jpg

[Old Tele man]

...different "quality" tubes? or maybe just effects of higher AC-line voltage from the wall (110-115VAC then, now 120-125VAC)?

[Structo]

I can't make out the values on the pic but such things as different cathode resistors and or plate resistors, grid resistor values all change the voltages.

[Old Tele man]

...I *think* the two schematics have identical component values, which is part of his question of "why the difference?"

[John Phillips]

One of the diagrams (probably the old one) may be wrong here too, as in your other thread. Even if they're not and were actual measurements, a difference of only 10% is nothing to worry about - it could be due to the particular tube that was in the circuit when it was measured, the line voltage, the resistor values (themselves 10% tolerance in the old amps), or meter error... or a combination of several of those things.

[BLC]

Check back further to the "C" connection on both schematics and see if the same value resistor is used just prior to that connection.