Fender Deville 100 ohm resistors blowing!

[SixAndChange]

How are you guys doing? Im coming into this forum hoping to learn something new here. Im a FOH engineer and one of my bands Fender Deville 212 decide to stop working whilst on tour a while back. We dont have a tech and I want to the core of my body to understand these things better.

Let me give you a little info.

A goodly sum Budweiser was spilled onto the top of the amp during a show one night, and shortly there after the amp cut out. I told the guitar player to shut off the amp and unplug it. After the show I plugged it back in and turned it on, at which point I noticed the area around the first 12AX7 was smoking, shortly there after the fuse blew and the amp shut off.

I took it apart later on and noticed that BOTH the 100ohm resistors (R80 and R81) had been burnt to a crisp. Now I only have a basic understanding of schematics and whatnot, but from looking at the PCB board, it looks like these resistors are connected to the powerlight and ground line coming from the input transformer.

My question to you is, what do you think is the cause of my problems here? would replacing these bad resistorss fix the problem, or would I only melt more components and blow more fuses?

ALSO, where can I go to read a little bit about the internal workings of the amplifier?


Thanks in advance for anyone that might help.

[stokes]

These resistors are an artificial CT for the heater circuit.Since beer was spilled into the amp it is hard to say from here what else is shorted out.You could try cleaning up the mess on the PCB's and change the resistors,but you are probably better off taking it to a tech.

[MWJB]

The 100 ohm resistors are blowing as a symptom of a deeper problem, probably shorts between the B+ (hi dc voltage to the tube plates) and the heaters (lo voltage, hi current AC). If you keep powering up without correcting this your amp may possibly catch fire before blowing the PT.

To play safe I'd replace ALL the tubes, thoroughly dry out (compressed air & hair dryer?) the PCB & tube sockets (clean/replace any tube sockets that have visible signs of arcing), replace the 100ohms and then power up (with no tubes installed) and look far any signs of hum/vibration/smoke/flames or burning 100ohms. If ok, start installling the tubes, one by one (obviously powering down between installations), starting with the power tubes (set negative voltage at pin 5 to around -55 to -60vdc first), until you have all tubes installed and no problems. Then bias the power tubes to 30mA (see the amp's manual).

If you can't get all the tubes installed without a problem then go to a tech.

Put the amp in standby mode, when unplugged from the wall AC, to eliminate the risk of getting a zap from the filter caps whilst working on the amp (the deville's main filter caps have bleeder resistors that drain the caps).

[Enzo]

I'd make sure the amp was thoroughly dry before applying any power.

The simple test is to remove the tubes and power up the amp like he said. if it seems OK, and no sockets start arcing, then you can reinstall the tubes and see what happens. Usually those resistors burn when a power tube shorts a high voltage anode to the heater. But with fluid in the amp, it could just be the fluid.