Troubled Princeton Reverb build

[Herzog]

I have a PR build here experiencing a difficult birth.

Once built I powered up with light bulb limiter, all seemed fine to proceed, voltages checked out, bias voltage present.

Installed tubes. Hooked up my bias probe but put this on the GZ34 tube. When I realised this I powered down and continued with tests. Amp seemed noisy (hum).
I installed a known good rectifier which arced under power. Plate volts reached about 190v before I powered down. (I maybe imagined this)

It turns out I destroyed my bias tester plugging it into the rectifier socket. The other day it was reading 150mv on any 6V6 I tried. Once I ascertained this I got a new bias meter today and began testing the amp again. Biased up nicely with an older set of JJs. (more on these below)

Sounded fine but lacked clean headroom. Moved the NFB to the 8 ohm tap of the OT. Seemed to clean it up a good bit but when testing the reverb I got a very loud distorted signal and no reverb.

I discovered the reverb transformer common was isolated from ground as was the 220k grid leak resistor. Sorted this out,

Plugged in to test and the 1K 3watt dropping resistor burned up.

Any clues where to start?

I had two sets of 6v6s I used in the blown probe, thinking they were bad, is it possible this was down to power tube failure? Each tube used in the probe got very hot and read bias at 150ma albeit for a very short time till I powered down. Any ideas here very welcome

Thanks in advance

[Stevem]

I have no clue what your taking about here!

There is no 220k resistor anywhere to be found in that amps whole reverb related circuit!

Also that 1k power supply resistor does not need to be 3 watts, as its only 1 watt in the Fender circuit!

If your starting to burn up that 3 watt 1k resistor that is 2 power supply dropping resistors away from the reverb circuit and in that case you have a output stage short going on, because if the issue was in the reverb circuit you would be burning up the 18k resistor that powers the last 12ax7 tube next to the output tubes which is the phase splitter.

I suggest you go to the Fender amp field guide site and look at the chassis layout drawing for the AA1164 PR amp and compare it to your build.

[Herzog]

Thanks for your reply.

The 220k resistor in question is the grid leak resistor on V3a, the reverb recovery tube.

If your starting to burn up that 3 watt 1k resistor that is 2 power supply dropping resistors away from the reverb circuit and in that case you have a output stage short going on, because if the issue was in the reverb circuit you would be burning up the 18k resistor that powers the last 12ax7 tube next to the output tubes which is the phase splitter.

This very is useful, thanks. Is it possible the output tubes have shorted causing this? Screen resistors?

This is my second PR build, the other one is built exactly the same and works perfectly. I use Rob Robinette's excellent layout drawing.

[sluckey]

There is no 220k resistor anywhere to be found in that amps whole reverb related circuit!

Sure there is. It's the reverb recovery grid resistor and is physically mounted on the reverb pedal jack.

If your starting to burn up that 3 watt 1k resistor that is 2 power supply dropping resistors away from the reverb circuit and in that case you have a output stage short going on, because if the issue was in the reverb circuit you would be burning up the 18k resistor that powers the last 12ax7 tube next to the output tubes which is the phase splitter.

That 1K feeds the output tube screens as well as the reverb driver.

[Stevem]

I ment to post , on the whole reverb driver / transformer side of the Reverb circuit.

If your output tubes are good and you replace that 1k resistor and confirm that you have atleast a - 32 volts on pin 5 of each output tube socket before you plug them back in, then the amp should play normal.

This assumes you have v+ also on pins 3 and 4 of each output tube .