I've isolated a problem on my Peavey Mace Tube Amp circuit board. Can anyone tell me what the gray cylindrical object with the burn marks under would be referred to and if you know where I can get one. I tried googling the numbers I could read on it but nothing came up. Thanks for your help.
An externally hosted image should be here but it was not working when we last tested it.
You will need an ohm meter to measure the resistor, preferably out of circuit but I predict he's still okay.
The burned marks underneath could have been prevented by placing the component higher above the PCB.
Most important are the solder joints on the other side of the PCB.
I bet they need to be redone.
/Hugo
The burned marks underneath could have been prevented by placing the component higher above the PCB.
Most important are the solder joints on the other side of the PCB.
I bet they need to be redone.
/Hugo
It's a 10 watt power resistor. The other numbers will tell you what the resistance value is supposed to be - within 10% as marked. If you want to either post all the text that is printed on the resistor (or post a pic that shows it all) anybody here can tell you what the figures mean.
Replacing the resistor will be relatively easy, but it would also be a good idea to find out why it happened so it doesn't happen again, possibly taking out other components with it. Going for a higher power rating is also not a bad thing ie, if you find a 12 W or 15W you can use it.
Replacing the resistor will be relatively easy, but it would also be a good idea to find out why it happened so it doesn't happen again, possibly taking out other components with it. Going for a higher power rating is also not a bad thing ie, if you find a 12 W or 15W you can use it.
nhuwar said:
An earlier post said it "supplies high voltage to the output tube screens". The name Peavey in the first post implies guitar amp. I'm thinking about sustained drive in excess of clipping, and just plain way too much screen current. I'm not sure what's involved with the "phase inverter transistors", but I'm sure they draw current too.
400 ohms at 10 watts should be good for 160 mA. Exceed that for too long, and poof. It looks like the resistor was mounted a little close to the board for a 10 watt part anyway.
You are correct as long as the resistor was sized correctly in the first place. Peavey is usually fairly conservative when it comes to part selection. Either two filter capacitors (they are in series) on the PS board are shorted or you have a bad tube. Though R1(400 Ohm/10 Watt) does supply the phase inverter the two smaller series resistors(22K/1W) would have given up long before R1. I say you have a bad tube that may or may not show up on a tester. Is the resistor in fact bad or when you saw the melt down you assumed it was bad? Another possibility is prolooooooooooonged usage in the "overdrive" mode, maybe with a incorrect load. There are 100 Ohm 5 Watt resistor s for each output screen (pin 4), check those for open. Caps or tubes thats all there is.
Craig
Craig
Up the fuse beyond spec, add parallel speakers, play loud and long and voila! Toasty resistors and transformer coils oozing their coatings. 
I was a kid once, good times. Blow it up then build it better. I can't think of anything more fun. The really cool part about tubes; in many cases it is hard to destroy the speakers. Sorry for the meandering off topic but the image in the first post brings back good memories.
I was a kid once, good times. Blow it up then build it better. I can't think of anything more fun. The really cool part about tubes; in many cases it is hard to destroy the speakers. Sorry for the meandering off topic but the image in the first post brings back good memories.
FWIW, I worked on a Peavey Valve King 100 today and thought of this thread. It uses the same 400 Ohm/ 10 Watt resistor. It was all I could do to get 40VDC across it, meaning, in a properly functioning amp the most it dissipates is 4 Watts. I still say bad tube(s). Also the power supply uses 100UF/550V capacitors from Nippon Chemicon. I looked on their website but these must be made for Peavey as I could not find anything over 450V. Anyway I thought they would make a nice big filter bank WITHOUT stacking them, doubling capacitance with the same number of caps as long as your PS is under 550VDC.
Craig
Craig
From the first post I didn't undestand if there is really a malfunction problem or just the aspect of the fried PCB. It looks like the burn is from a previous dead resistor and who changed it mounted the new one too close. Maybe a better lighted picture will clarify this, but IMO this resistor doesn't look like an old/overloaded one...
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