1968 Gibson Super Medalist all tube amp

[G.A.S.Asylum]

I got this amp recently and it looks great, amazing cosmetic condition and all electronics look good inside. Everything original , including the tubes , but the two 7591 power tubes are shorted, so I ordered a new matched pair. 
my task now, is to find information about the bias setting for it. 
this, and any other information about the amp , would be great, even if it’s not technical. 
thanks, best regards. 

[badbluesplayer]

I don't know much about them.  I just looked at the schematic.  here -     https://schematicheaven.net/gibsonamps/super20_medalist.pdf

It looks like the bias is not adjustable.  Just install new tubes and go.  You should be measuring about -8.7 volts at pin 6 of the new power tubes.  The schematic says +8.7v, but it should be -8.7v.  

[Bill Moore]

Is the "Hum Adjust" something like the Silverface Fenders used to balance voltage between the power tubes?

[badbluesplayer]

The hum adjust looks like it adjusts the difference between two small cathode resistors on the power tubes.  An unusual way to adjust hum.  Not the usual way of varying the voltage on the two legs of the heaters.