CBS SF Princeton PS node

[Steelwitch]

Hey y’all,

I got a sf princeton reverb with a burnt up 1k 1w resistor where the screen grid of the output tubes are getting V. This is due to a short from the screen grid to the cathode? Am I right in thinking this? Here is the schematic. Thanks!

[Steelwitch]

The caps are testing normally, so it is the only other failure I could find related to this PS node

[The Dude]

Most likely a shorted or intermittent output tube. Replace the resistor and pull the output tubes. See if the resistor holds up with no output tubes installed. If so, you've eliminated other possibilities.

[pdf64]

Yes, it’s probably either the screen grids or their HT cap, or V2 reverb driver, drawing too much current.
Use a metal oxide type with a flame retardant coating as a replacement.
Power up via a light bulb limiter until you’re sure all is good.

[Helmholtz]

To see if there's excessive current just measure the DC voltage drop across the 1k resistor.
Should be around 10V without and around 20V with power tubes.
1V drop corresponds to 1mA.
Filter cap leakage or a shorting reverb driver (V2) would show as increased voltage drop.

Voltages measured without limiter.