Mesa Boogie Rect-o-verb

[methodofcontrol]

hey guys,
i have one of these on my bench i'm fixing for a friend. the amp just started sounding quiet and fizzy at some point after my buddy loaned it to another band on tour. i opened it up to have a look and one of the 1k2w resistors on the power tube circuit board is charred and terrible looking. i assume that's why the amp sounds so shitty...
but my questions are:
1)how does this happen? (bad power tube? voltage spike from wall?)
2)if i replace the resistor, how do i know i'm not just fixing the symptom and not the problem?
3)any good tips on removing carbon from a circuit board?
4) ok to replace these resistors w/ 1k5w's? (i know increased wattage is not a big deal, but i don't want it being one those things where the bigger resistor allows something more expensive to burn up if the problem persists- resistors are cheap!)

thanks for the info!

[Wilder Amplification]

hey guys,
i have one of these on my bench i'm fixing for a friend. the amp just started sounding quiet and fizzy at some point after my buddy loaned it to another band on tour. i opened it up to have a look and one of the 1k2w resistors on the power tube circuit board is charred and terrible looking. i assume that's why the amp sounds so shitty...
but my questions are:
1)how does this happen? (bad power tube? voltage spike from wall?)
2)if i replace the resistor, how do i know i'm not just fixing the symptom and not the problem?
3)any good tips on removing carbon from a circuit board?
4) ok to replace these resistors w/ 1k5w's? (i know increased wattage is not a big deal, but i don't want it being one those things where the bigger resistor allows something more expensive to burn up if the problem persists- resistors are cheap!)

thanks for the info!

Those are more than likely the screen resistors and it was probably that tube that had a screen short, which took the resistor out. Very common occurance when power tubes short.

Yes it's OK to increase the power rating. Not sure on how to get the carbon off the board though.

Sounds like a retube is in order. The problem was caused by that tube shorting to the screen. Replace that resistor along with the power tubes, rebias and you should be good to go.

[acorkos]

3)any good tips on removing carbon from a circuit board?

at my 'day job,' i'm a dentist...i have compressed air and one of these...

the microetcher blows 50 micron aluminum oxide powder at 60 psi....it removes the top layer of carbonized pcb nicely. the stuff can make a mess...i lay a towel over the amp and expose just the area that needs treating (like surgery), and blow out all the powder afterwards.

4) ok to replace these resistors w/ 1k5w's?

i see plenty of these on EL34 amps...

[methodofcontrol]

cool, guys!
thanks for the reassurance.
i'll replace both screen resistors and power tubes and try the amp out. i'll post back later!