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Old 11th April 2009, 06:36 PM   #1
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Default Does Anyone Know What This Is?

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.

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Old 11th April 2009, 06:47 PM   #2
Shenda is offline Shenda  Bosnia and Herzegovina
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Some 10W resistor... I can't read value in ohms...
...probably
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Old 11th April 2009, 06:57 PM   #3
Netlist is offline Netlist  Belgium
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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
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Old 11th April 2009, 06:57 PM   #4
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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.
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Old 12th April 2009, 02:51 AM   #5
llwhtt is offline llwhtt  United States
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According to the schematic it's a 400 Ohm, 10 Watt resistor. Supplies high voltage to the output tube screens (490VDC) and phase inverter transistors (300VDC).

Craig
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Old 13th April 2009, 03:33 AM   #6
DHT112A is offline DHT112A  United States
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Got a pic of the other side of the board?
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Old 14th April 2009, 01:43 AM   #7
nhuwar is offline nhuwar  United States
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The question I have is why did it fail. I could be wrong but I though failed resistor are usually a symptom and not a cause.



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Old 14th April 2009, 02:02 AM   #8
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Quote:
Originally posted by nhuwar
The question I have is why did it fail?
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.
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Old 14th April 2009, 02:32 AM   #9
llwhtt is offline llwhtt  United States
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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
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Old 14th April 2009, 02:37 AM   #10
llwhtt is offline llwhtt  United States
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Ty,

You beat me to the sustained overdrive reply!

Slow typerer,
Craig
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