Peavey Triumph 60 Hum

[Lostfollicles]

Damn! while checking the HT voltage to set bias on my now tweeked Peavey Triumph 60 running EL34's the meter probe slipped and shorted the HT to the LV heater circuit, didn't blow any fuses after the pop but it slowly developed a 50Hz hum on the Crunch & Ultra channels??? Clean channel is hum free???
All channels work fine but I'm only getting hum on the dirty channels! Any ideas what I've buggered guys?
I've checked DC to valves V1 V2 V3 and all looks OK but then I don't have a scope to check for any nasty ripple!

I have looked at the circuit for any other problems and found there are two 47 Ohm flameproof resistors R70 & R71 that are open circuit! Could this be why I now have hum?
I read somewhere these low ohm resistors are there for reducing the hum in tube heater circuits by lifting the voltage above ground?? I know they are open circuit but surely it would hum on the clean channel too which it does not, not even a hint!
It's an easy fix of course but I'm just trying to get my head around how the short got to blow these resistors!
Thank you all in advance for any help and advice!
Regards

[loudthud]

The short is what blew the resistors, but after they blew the HV on the heater circuit could have broken down the insulation between the heater and the cathode of some of the tubes. Replace the resistors to see if that fixes the hum.

[Lostfollicles]

Thank you loudthud!
Replaced those ground lift resistors R70 & 71 - 47 Ohm FP today and that nasty hum on the Crunch & Ultra channels has gone!

And there I was just about to replace every cap on the pre-amp board thinking it was a leaky cap! Doh!

Every day is a curve ball challenge!

Regards
Lostfollicles