Variac

[J Forster]

It depends on the circuit.

If the rectifiers are tubes, it's better to use something like a light bulb, because the caps don't get voltage until the rectifier heats up.

If the rectifiers are solid state, absolutely use a Variac.

I generally apply HV from an external PS with no filaments power in the unit being tested and always check the prints and reform the caps, before applying line.

-John



Bob Groh WA2CKY wrote:

> The answer is "very, very important!".
>
> Sometimes you can get away without doing so but not always - don't know what percentage of old gear will 'complain' (usually by venting smoke and noxious fumes as the power supply electrolytics let go plus the possibility of frying a power transformer) but having it happen even once is not a good thing. Don't ask me how I know that (you can guess thou')!
>
> I guess that probably better than 50% of the old gear I bring up has a bad or about to be bad electrolytic.
>
> By the way, you need more than just a variac. You really should monitor the power supply as you bring the voltage up. Sometimes you can reform the caps and they will be ok but usually (again just my opinion) a bad cap is a bad cap and it will still fail. You can usually detect that because the voltage on the cap stops increasing as you bring things up (and it will usually start to run hot).
>
> I have come to the opinion that I should just plan on changing the electrolytics for new ones even before I bring up the radio. Haste makes waste. If the cap(s) don't fail now they will probably fail pretty soon so just go ahead and change them out right at the start.
>
> Bob, WA2CKY
>

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