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I have a 1200S here with a BBQ'd load resistor. Can't decipher the band code, but this closest matching schematic suggests a 680ohm 1W across the 16ohm secondary. In this amp it's a 2W CC resistor..
Sunn Dual Rectifier Amp-1.pdf
I can't imagine a fault condition, other than no-load, that would cook that resistor.
The owner plays loud through a custom cabinet, which he says is working fine.
Lets say the cab, cable, and jacks all check out, what else?
I thought of flyback voltage, but that would appear on the primary side...
The Sunn 1200S schematics at the Hoffman amp forum show that 680 ohm as a 7 watt resistor.
Sunn Schematics - Tube amp Schematics
And that amp driven balls to the wall can easily give you some 200W squarewave.
Now the resistor doesn´t know or care about waveforms, it will happily heat up.
In that case, the resistor will be asked to dissipate almost 5W, so 7W is minimum.
Original schematic *might* have asked 10W and one digit was lost along the way.
Used as a PA, no big deal, voice is (hopefully) used clean, but as soon as you plug a Guitar (or even a Bass) there and rip off, all chips are down.
Juan Manuel Fahey
I can't even count the number of times I've replaced resistors that were under rated for what players do with the amps. Though I'm with Juan on this, Perhaps a 10W spec typo'd to 1W? Still, there are a few cases here and there where a truely vintage amp driven balls out is up to the task but for a couple of resistor ratings.
"Never bet your life on somebody else doing their job." SoulFetish's good friend
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A
"Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158
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