I have a pair of Mark IV amps. They very clean inside and out. The EL 34 are close to original with "Dynaco by Mullard" on the side. The 7199 is two years old and never used. I replaced the can capacitor because it got hot. I replaced the bios diodes and caps. I replaced the black paper caps with polypropylene. Both amps have a fairly loud 120hz hum before and after the changes. I tried new EL34. No change. I replaced the GZ34. No change. The voltages are:
GZ34
2,8 - 485v dc
4,6 - 388v ac
EL34
1,8 - 1.56
3,4 - 475v dc
5 - -35
7 - 2.8 ac
8 - 3.4 ac

Does anyone have other ideas about eliminating the hum?

Thanks. The connection is good, solid soldier, the same as the diagram. Both amps have very good assembly. They look exactly the same so I assume factory wiring. This weekend, I replaced the pc board resistors with new carbon resistors. A few of the 1 watt resisitors were out of spec, lower than they should be. I'll turn it on Saturday.

The amp turns on fine and the bias did not change after the resistor change. The hum is still there. I might try increasing the filter capacitance, one leg at a time.