Early Ampeg Reverberocket R-12-R Chassis Restore

[misterc57]

That's what I'm asking, what is the measurement you are reading? Or how do you know it is fuse blowing current?

Monitoring my variac meter for current as I very slowly dial up the AC line input. Current rises very slow (normal), then starts getting jumpy with small hops (not normal) at around 20 VAC input, then huge nearly 1 amp swings as I continue to dial up slow. This is when I back off.

This is all happening around 20 to 25 VAC input, no tubes installed, and 6.3 VAC secondary wires lifted.

Update

This morning I lifted the 5 VAC secondary. Instead of the jumpy small hops I now get the huge 1A spikes at around 20 VAC input.

Not much left to rule out aside from the PT?

Thank you

[Helmholtz]

Disconnect really all PT secondary leads and isolate them, i.e. everything but the 2 primary wires.
Now try again.

[misterc57]

Disconnect really all PT secondary leads and isolate them, i.e. everything but the 2 primary wires.
Now try again.

Did that, Still happening. After which I lifted primary leads and attached a test AC cord. So now PT is completely isolated from chassis circuit and issue is still happening, Still at around 20 VAC line input.

Bad PT.

[Helmholtz]

Bad PT.

Well, as said 7R primary DCR looks too low.
Probably shorted primary turns. In that case the primary impedance essentially reduces to the DCR.
Means that an input voltage as low as 7V can draw a mains current of 1A.

[drewl]

I have a couple old Ampegs with bad PT's in this week.
seems quite common, either from abuse or asking too much of the PT.