Re: 545B


 

Craig Sawyers wrote:
Hi all
Well, I bought a 545B, known not working. HT power supply was completely
unwired. Wired it back up - and here is what I see:
* 6AU5 oscillator is going at 50kHz, which is pretty much OK. Voltage
produced is 15V rms, which is low by a factor of 10 or so, and the plate of
the tube glows red.
* Tube voltages all over the place - for example the book value of the grid
voltage is -55V, and it reads near ground.
* Capacitors around that tube measure OK, values correct, <10^8 ohms
insulation resistance.
Some thoughts...

I wouldn't assume that the caps weren't the problem, particularly that .001uF 1KV "leakmaster" oil cap used in the oscillator tank circuit. It can look good until stressed. Try hitting it with some freeze spray and see if it changes anything. This part is cheap enough to replace as an experiment.

You might also try a 6AU5 replacement.

Perhaps a short in the HV circuitry is loading the oscillator down.

-Dan

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