Vintage tube amp resurrection with Variac?

There is a simple way to do this using an incandescent light bulb. You remove all tubes and put the light bulb in series with the AC power and turn it on.

The light bulb will light up, which means most of the power is being dissipated by the bulb because the caps are likely shorted. However, if they need to 'form up', the bulb prevents them from heating up by limiting the current. If the bulb goes out the caps are formed up and OK.

Time-honored technique BTW; but if this is an amplifier you intend to really play a lot don't screw around- just change out every filter cap in sight... If there is a selenium rectifier change that out too.

If using a variac on a unit with the tubes installed care needs to be taken if the item is tube rectified.

If it has a slow start rectifier installed it will NOT see a slow ramp up from the variac, but will eventually quickly see higher voltage, which is not good for reforming caps.

There are some quick start subs for a GZ34 (think I once used a 5Y3, but not certain as it's been awhile).

A local tech once used a SS (plug in) rectifier on one of my vintage amps with a GZ34 (he made made it in a manner of minutes), but I've seen them for sale online as well.

With tube rectifier things get simpler because tube rectifiers reach operational voltage slow enough to catch problem with or even without variac.
With variac set to operational voltage and voltmeters attached to the bias pots or resistors and one attached to the rectifier output you can monitor gradual voltage increase. Once bias on any of the bias pots goes beyond tolerant, you can bring back variac to the noted voltage or below or turn amp off and inspect circuit elements around the fault bias pot or resistor.

Czarivey:

Your advice does nor gell with the tech that worked on my Pilot 232, nor the advice I received from the AA forums.

Basically I was told that a GZ34 will not start to pass current until it reaches 80-90 VAC (which is 4-5 times higher than one wants to start when reforming lytics).

Dekay I mentioned earlier replacing all DC supply caps before even getting onto the variac.