500C - 7591 killer

Wall voltage is 125VAC. Got -20.5V off the bias cap with the 2 CL-70s. I'm just nowhere close with the -13 as the best it can do after the IBBA. I used 20K bias pots and 10K balance pots.

I have 435V on the plates, 403 on the screens, and had -16.6 as the best bias I could do with the old 10K bias pot before I did IBBA.
 
Did you Replace C-91(4 section Can cap) and R143 (big green 1.2K 7W resistor between the 2nd and 3rd output tubes?). Your screen voltage should be a bit lower than the plate voltage. Singles, restuff or new can cap?
 
@Jailtime Did you ever sort this out?

I have a IBBA board wired in (500C with 7591s). Before inserting the output tubes, I powered up the unit with the line voltage reduced to 60V and a DBT in series (100W bulb). The max negative bias voltage I'm seeing at the grid resistors is -6V, which seems too low, even with the line voltage at 60V. So I'm a bit wary about putting in the output tubes. . . .

FWIW I do also have a CL-80 thermistor installed and a Rectron BR84 rectifier.
 
@Jailtime Did you ever sort this out?

I have a IBBA board wired in (500C with 7591s). Before inserting the output tubes, I powered up the unit with the line voltage reduced to 60V and a DBT in series (100W bulb). The max negative bias voltage I'm seeing at the grid resistors is -6V, which seems too low, even with the line voltage at 60V. So I'm a bit wary about putting in the output tubes. . . .

FWIW I do also have a CL-80 thermistor installed and a Rectron BR84 rectifier.
I think he ended up selling it but I am not 100 percent sure.
 
Wall voltage is 125VAC. Got -20.5V off the bias cap with the 2 CL-70s. I'm just nowhere close with the -13 as the best it can do after the IBBA. I used 20K bias pots and 10K balance pots.

I have 435V on the plates, 403 on the screens, and had -16.6 as the best bias I could do with the old 10K bias pot before I did IBBA.
Mine kepting redplatting at 125VAC hopefully my bucking transformer fixes this... Got it a month ago. So far so good
 
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