Old Princeton Reverb keeps blowing fuses

[dancriel]

Hi, I'm new to the forum.

I have an old (65 or 66 maybe?) Fender Princeton Reverb amp that's blowing fuses. When I turn it on, as soon as the tubes warm up a little, the largest, leftmost tube makes some blue spark action inside the glass and the 1 Amp slo-blo fuse blows...any ideas where should I start my troubleshooting?

This amp sat dormant for a couple of years before I started using it again. I know very little about this stuff, so any help would be greatly appreciated.

Thanks.

[Jerry]

Replace the fuse with the proper rating and remove the output tubes. That would be the 2 large tubes to the right of the first large tube on the left. If it still blows a fuse, you have a problem with your transformer, or rectifier tube. If it doesn't then you have a problem further downstream. possibly ouptput tubes or filter capacitors in the power supply. You should locate a schematic for it.

[Enzo]

The sparking action inside the tube says that tube is bad, to me.

[dancriel]

Hi Jerry,

I tried what you suggested - replaced the fuse with a new one, removed the 2 output tubes, and switched on the amp, and the fuse *did not* blow. Would this mean I probably just need new tubes? The ones I have in there are at least 7 or 8 years old.

[Don Moose]

I'd be a little bit worried that either the bad tube took something with it, or the internal spark is a symptom of a non-tube problem.

You _could_ take the tube that doesn't spark and try it in sparky's socket - but that may kill a good tube. You _could_ try sparky in the other socket, but that could kill parts inside the amp.

You might wander over to R.G.Keen's Tube Amp Debug pages and see what he suggests for something like this. Don't go outside your personal-safety comfort zone, though. The voltages inside a tube amp are genuinely lethal and we don't want to lose anyone.

Hope this helps!

[52 Bill]

But the leftmost tube from the rear of the amp is the rectifier, not an output tube.

I'd suggest replacing the rectifier tube first and then see what happens.

Removing the two power tubes will have removed the major current load from the rectifier causing the tube not to spark and the fuse not to blow.

[txstrat]

I'd go with ENZO.
Sparks inside a tube don't sound good to me either.
When the new fuse does NOT blow with the power tubes out - what would I assume? Bad tubes.
I'd replace the tubes and see what happens before I would troubleshoot any further.

Matt