Ampeg Gemini II 7591 bias questions

[NeilG1203]

Hello again,

Hoping to get some guidance on what numbers to use to properly bias this amp, after installing new EH7591s.

Without adjusting anything except the AC with a Variac, setting voltage to 115 VAC and using an Alessandro biasing unit, I am getting 34 mA per 7591, Volmeter - screen voltage ~ -22, matching the Ampeg drawing.

When I look up the 7591 spec sheets, for an AB setting, there are 3.

NJ7P SQL Tube Database Query

I think this is the correct set of parameters from the above link:

Push Pull Class AB1 Amplifier
Plate Voltage ................................. 450 V
Grid No. 2 Voltage ............................ 400 V
Grid No. 1 Voltage ............................ -21 V
Peak Grid No. 1 Voltage........................ 42 V
Plate Current (Zero Signal) ................... 66 mA
Plate Current (Maximum Signal) ................ 144 mA
Grid No. 2 Current (Zero Signal) .............. 9.4 mA
Grid No. 2 Current (Maximum Signal) ........... 30 mA
Load Resistance ............................... 6.6K Ω
Power Output (approx) ......................... 45 W

Not sure if this is for one PT ot two??

Confused by the 45 watt power out (thought the Gemini II had about a 30 watt rating)

Any help with a pin by pin recomendation or other comments would be very appreciated.

Thanks in advance.

Neil.....

[Jazz P Bass]

The 66ma current draw at idle is for two tubes.
All else is up for grabs as far as I can see.
How does it sound?

[NeilG1203]

Thanks for the quick reply.

Unless I'm reading it incorrectly, there is only 5 volts diff between the plate and screen(grid 2).

I'm new to the sound/tone but I'd say it's very close to what I am looking for, matched with my single coil archtop.

Trying to trace/track down the source of a hum in the reverb - increases as I turn up the reverb pot. Sounds like 60 Hz. Acquiring a scope to help.

Changed out all the electrolytes but am concerned I did not properly charge them. Also changed both transformers (Mercury Magnetics) and this introduced a low level hum.

Comments and suggestions are very welcome.

Thanks!