Re: Mystery power supply , preamp and power amp!
Even a variac may not do the job. At low variac volts all the valve heaters will be too cold for the cathodes to emit. Nothing will happen. So you'll wind the variac up and up and up and eventually current will start to flow. But the mains transformer will now be supplying quite a lot of HT. The caps might be OK or they might not.
Specialised capacitor reformers have been developed to do just this job and if there was any other safe way then they wouldn't be needed. They're not difficult to fettle up. A couple of solid-state diodes and a suitable resistor tacked onto the rectifier socket pins can do the job with all the valves removed (just check that none of the other caps in the circuit will be over-volted). It would be a shame to do damage rather than doing this right.
Cheers,
GJ
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