Ok. Let’s try this again…RCA 9TC240 Alignment

[Penthode]

It is a transformer set. When working on hot chassis sets, I always use an isolation transformer. On these set? No need.

What you do is replace the AC filter capacitors. The ones from the AC supply in to chassis. Use only 1000v dc capacitors or ones rated for 600v ac. Once replaced use an ohmmeter from each prong to chassis to confirm no problems. The is no resistive leakage here so the reading will be more than 50 Megohms so off the scale of most of your meters. And thats it.

So no on this and other full transformer sets like this, no isolation transformer is needed.

I suspect your isolation transformer is dropping the supply to 95 volts ac.

But put it this way: if th supply is 120vac, I would expect the filaments to be about 6.5v ac. Because it is only copper wire and a fixed transformer ratio, it is impossible to have the low filament voltage you cited unless there is a resistive drop someplace (which will dissipate a lot of heat) or the losses in the isolation transformer are causing the supply to the set droop when on.