#1
I have been trying to fix this weird hum coming from my marshall valvestate 8080 and so I bought some electronic cleaner and sprayed all over the inside of the amp and pots. Good news is that it stopped the pots from scratching whenever I turn the knobs but the hum is still there and whats worse is that these (resistors?) near the tube of my amp start to burn and smoke. I've opened it and tried to see why it burns but no luck. It would take about 5 seconds before I can smell the burning coming from the (resistors?) I've taken a picture of the it. I don't want to take it to a repair shop since they charge $45 an hour and this amp cost me about $20. If you amp builders can help me out I will totally appreciate it. Thanks.

Last edited by Scarface735 at Dec 13, 2011,
#2
Sadly I cannot help you, but PM Cathbard. Explanation is not necessary.
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#4
Power = I^2*R.

If the resistors are burning up, you've exceeded the power rating on them.

Maybe you shorted something downstream of the resistors, and there is a large current going through the resistors, which is causing the power rating to be exceeded.

Just my guess, I'm not too familiar with amplifiers though.

(Power also equals V^2 / R. I doubt a large voltage is being dropped across the resistors but anything is possible)
Last edited by farmosh203 at Dec 13, 2011,
#5
^ I figured since they are heating up very quickly they must be taking in alot of current since they heat up very fast. On the otherside of my amp there are similar resistors that are a bit smaller that I just noticed today also heat up quickly.
#6
YOU SPRAYED THE ENTIRE INSIDE OF THE AMP? Whats happening then is probably that the resistors are getting hot (which the often to at regular operating levels) and the chemicals are burning.
#7
^That may be a problem too. Should I use a contact cleaner to dry it? The ones used for computers?
#8
You can clean it with a toothbrush but you'll probably just have to wait until it burns off.
As for the hum you probably have to replace the filter capacitors. That's where I'd start.
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#11
No I believe my house has some good wiring. When I purchased the amp, the hum was coming from the amp already and he suggested that it was the speaker (which i know is working 100% fine). It may be the power cord that is causing the problem so I'll go ahead and test that.

My amp is covered in greasy deoxit so that maybe why it burns so I'll give it a cleanout with a toothbrush and report back.
#13
hold an intervention. smoking is the number one killer of amps in the world
Call me Chris
Quote by jimihendrix6699
had a blast until the person in front of me whipped out his dick and started pissing all over the floor..

Ducks and guitars or fish and guitars. I lead a simple existence
#14
I cleaned it with a toothbrush and so far it seems like its working. The resistors are extremely hot. I hope thats how they are supposed to be. It still smells like its burning unfortunately but I'll test it out tomorrow again.

As for sound I will change the caps as you mentioned and see if its causing the problem of the loud humming.
Last edited by Scarface735 at Dec 15, 2011,
#15
Quote by inkandlead
And the hum is definitely not our guitar/pedals/cable?


And its not that. I have another amp as well so I'm sure.
#16
maybe get a small fan in there
Call me Chris
Quote by jimihendrix6699
had a blast until the person in front of me whipped out his dick and started pissing all over the floor..

Ducks and guitars or fish and guitars. I lead a simple existence
#17
Quote by IronMaiden76
maybe get a small fan in there


I never heard of a solid state amp with a fan. I understand theres a preamp tube in there but I think its there as a gimmick. It doesnt seem like it even affects tone.
#18
The photos don't indicate browning of the resistor bodies, as would be the case if they were dissipating more power than their rating. Theyd certainly be browning if the burning was the actual resistor body going up in smoke.

They look like good size power resistors too, they are designed to get hot, so it's really no surpise that they are getting hot.

At this stage I'd go with whats been suggested that the heat is still burning off the chemical residue.

I'm assuming the amp hums with no guitar connected to the input?
#19
when you plug it in, do it outside so if whatever is burning off catches fire, you don't burn the house down.
#20
Quote by Scarface735
I never heard of a solid state amp with a fan.



MG's had them in the back and they're loud as hell too. I'm guessing it functions like a rattle in the sense of a rattlesnake: Back off and walk away.



Back on topic. If you're worried about the resistors getting too hot try probing around them with a multimeter to see if it's still within tolerance. If it is then see how much current it's dealing with. Just be careful to not to discharge the caps on yourself while poking around.
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#21
^the MG's i played through were quiet...
Call me Chris
Quote by jimihendrix6699
had a blast until the person in front of me whipped out his dick and started pissing all over the floor..

Ducks and guitars or fish and guitars. I lead a simple existence