6G3(-ish) Amp Popping Fuses--Need Ideas!

[pjhalliday]

I have an amp that is basically a 6G3 clone that was working fine, warmed up fine at a gig, was switched off then back on and has been popping fuses ever since. Fuses pop even going to stan-by and also pop even with all tubes removed. I have not found a short to ground from any of the power transformer wiring and cannot figure why I'm blowing fuses with the tubes and even the pilot light removed. If you have ideas about diagnosing a problem like this, please suggest ideas! Thanks.

[Jazz P Bass]

What type rectifier are you using? Solid State or Tube?
(A basic schematic would be nice.)
If it blows a fuse with the GZ34 rectifier (if that is what you have in it) removed then you have a power transformer problem.

[pjhalliday]

It does have a GZ34 rectifier and pops with that removed. The layout is very similar to the schematic here except that the input jacks are hi only and the first preamp stages for the inputs do not share the same bypass cap/resistor.

[eschertron]

Are the heaters tied to ground with 100R resistors? with all tubes removed (and hypothesizing that the PT is not bad) something in the heater supply might cause the fuse to blow.
Also, do you have a light-bulb limiter? That's a good tool to have; allows you to keep the power on the circuit with popping fuses or damaging the amp further.

[pjhalliday]

The heaters are tied to ground with 100R resistors. From all points along the heater circuit I measure 50R to ground as expected (no shorts). I do not have a limiter, but could make one if it would be helpful.

[Mick Bailey]

My starting point with this would be to isolate the PT secondaries and see if it draws excess current without any secondary load or connection. Here's where the bulb limiter comes in.

If you're still getting high current draw then you may have an internal short, or arcing between turns. Transformer faults sometimes only occur under operational voltages.