Friend smoked champ

peteb

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I was jamming last night with a friend. We have been regular jamming partners for about five years. I really like jamming with him, he is a much more qualified musician than myself, but it is really hard on my gear. Usually, he travels, it’s only a mile, and I provide an amp. For some reason he is really hard on my gear. Over the years it’s always the amp he is playing that blows a fuse, a tube, or in this case the amp started smoking. I have never smoked an amp.

he said he noticed a problem all night. I plug straight in and he uses a pedal board. At the end of the night the amp was acting up, but it was still playing.

my friend saw a small amount of smoke coming out of Jack 2 and shut the champ off. I have not looked inside yet. It should be pretty obvious what was smoking. The under sized fuse, 0.5 amps, did not blow. I felt the trannies and they were both cool. i am sure the power tranny was cool because I turned the amps off for dinner. He is an actual musician and he thinks the amps should stay on, even old amps, during extended breaks. I turn amps off during long breaks. Vox says don’t leave an AC running with no signal.


what smoked? My friend thought it must be near the input because that is where the smoke came out. I think that is the only place it could come out.


all I can think of is the cathode resister fried.
 

schmee

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Open it. You should be able to play an amp hard with no ill effect. A pedal can drive an amp harder though. Original little alnico speaker? I wonder if those are paper voice coils? maybe he burned the voice coil up?
It's likely obvious inside though. Probably is a resistor and the input jack is an exit hole for smoke!
 

Timbresmith1

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Open it. You should be able to play an amp hard with no ill effect. A pedal can drive an amp harder though. Original little alnico speaker? I wonder if those are paper voice coils? maybe he burned the voice coil up?
It's likely obvious inside though. Probably is a resistor and the input jack is an exit hole for smoke!
Pretty much the only hole 😂
 

Axis29

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I had a guy come over to try my '69 Vibrolux Reverb. We kinda knew each other through The Gear Page. He';d never played through a Vibrolux, did I mind him come checking it out. Of course not... Why would I? Nice guy, plays big vintage Marshalls all the time... dimed, it seems.

He dimed my VR when I wasn't looking and blew both speakers (Weber P10Qs). I didn't realize they were blown for a few weeks (the amp didn't get used a ton during that particular period). When I turned it on, playing in a pretty quiet environment, I thought some tubes had gone microphonic... Took me a few minutes to figure out the speakers.

I stopped letting anyone plug into my amp when I am not watching. LOL

But, I will most certainly let folks play them. I used to host a bunch of Blues Jams, back in Virginia. Lotta guys loved playing through my gear. Never had any other problems with jokers plugging into my stuff....
 

Boreas

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What Champ model/circuit and era?

So he was plugged into Jack 1? If he was plugged into 2, it could have been the attenuator resistor on that input.
 

JL_LI

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I have a Mesa Boogie. Gain is in stages. Anyone is welcome to play using my settings. Turning it up a little or using one of the high gain channels is OK too. But if you have no idea how the thing works or how to control its temper, leave your cotton pickin' hands off of it.
 

Phrygian77

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Are you sure you checked the OT temp? I've seen a shorted 6V6 melt the varnish out of one, in a '80 Champ. No blown fuse. It also torched the cathode resistor.
 

roeg

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Caps and resistors smoke.

My last *smoking amp* experience, playing my '79 vibrolux, poof smoke. Turns out one of the big caps in the ...cap clamshell, gave up its guts. Re-cap and all has been well for several years now! routine maintenance issue, it happens(caps dry out and fry).just one possibility. as you stated, look for a blackened resistor(i don't know the champ circuit,but, i can get around a Hiwatt, or Marshall).
 
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cyclopean

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I had a guy come over to try my '69 Vibrolux Reverb. We kinda knew each other through The Gear Page. He';d never played through a Vibrolux, did I mind him come checking it out. Of course not... Why would I? Nice guy, plays big vintage Marshalls all the time... dimed, it seems.

He dimed my VR when I wasn't looking and blew both speakers (Weber P10Qs). I didn't realize they were blown for a few weeks (the amp didn't get used a ton during that particular period). When I turned it on, playing in a pretty quiet environment, I thought some tubes had gone microphonic... Took me a few minutes to figure out the speakers.

I stopped letting anyone plug into my amp when I am not watching. LOL

But, I will most certainly let folks play them. I used to host a bunch of Blues Jams, back in Virginia. Lotta guys loved playing through my gear. Never had any other problems with jokers plugging into my stuff....
An amp that can’t handle being dimed was either poorly designed or has something wrong with it. Especially if he was just playing guitars through it and not using some kind of pedal that self oscillates or a synth or something that’s going to hit it with a sound wave that it’s not expecting.
 

cyclopean

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What kind of pedals was your friend using?

If we’re trying to troubleshoot/keep it from happening again, that may matter.

I’m curious if he was running some enormous amount of gain/boost or something like that.

Anything with super high or low frequencies might damage a speaker but i can’t imagine it would hurt the circuit.
 

fretWalkr

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My only smoking amp experience was at a gig with a BFSR. It was a power transformer. Apparently a cap failed and the PT went up in acrid brown smoke which came out of the unused input jacks.
 

tubedude

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Generally, if an amp in otherwise good condition is driven hard and smokes, the screen grid resistor is the likely culprit. Especially if it was still working when smoke was detected. This happens a lot driving it hard using attenuators also.
 

OldPup

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The cathode bypass resistor or the cap next to it have to be the top suspects. I mean, it could be anything but I’ve had a cathode bypass cap blow in a VC I owned and from what I read online it seems pretty common. Champs are known to run that part of the circuit pretty hard.
 

jrblue

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Mega-doubtful that his input would have caused a problem in the amp. Even massive effects and gain produce a tiny signal, really. As others have pointed out, even up all the way the circuit, particularly in a Fender, is designed to handle the load. What mostly happens is that things get loose over time, and it's a loose part or a failed component that cause the amp to go out. That's really the cost of doing business, and Fenders, poarticularly, are designed to be put back into order if that happens. The PCB reissues are harder to service, but the older amps make it easy to inspect, test, and replace parts. Others can identify the most commonly failing parts, and where to look first. Good luck -- I hope and expect it will be straightforward. And as for this player advising you about leaving your amp on, etc., I'd simply say that it's your amp, so listen and then do what you want. It's a Champ. You can turn it off and on.
 

peteb

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screen grid resistor is the likely culprit.

OK, we have a suspect.

this is a blackface champ.

I kinda wanted to have an idea what to expect before I looked at it.

i probably am going to look at it today, but not planning to do anything about it. Too much other stuff I have to do.

I agree with the comments that an amp is meant to be played, and it should be no problem to let some one use it.


I have seen too much evidence that pushing the front end with something other than a guitar, I play single coils, is a contributing factor.

his volume was not overly loud, about the same as a champ on 8 with only a guitar. His pedal board has overdrive, and reverb and trem. Mostly I think he was running a small amount of overdrive.


thanks for the replies, I will let you know what I find out.
 

schmee

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Generally, if an amp in otherwise good condition is driven hard and smokes, the screen grid resistor is the likely culprit. Especially if it was still working when smoke was detected. This happens a lot driving it hard using attenuators also.

Screen resistor was my first thought also.

OK, we have a suspect.

this is a blackface champ.

I kinda wanted to have an idea what to expect before I looked at it.

i probably am going to look at it today, but not planning to do anything about it. Too much other stuff I have to do.

I agree with the comments that an amp is meant to be played, and it should be no problem to let some one use it.


I have seen too much evidence that pushing the front end with something other than a guitar, I play single coils, is a contributing factor.

his volume was not overly loud, about the same as a champ on 8 with only a guitar. His pedal board has overdrive, and reverb and trem. Mostly I think he was running a small amount of overdrive.


thanks for the replies, I will let you know what I find out.

Does a Champ even have a screen resistor?
 

peteb

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I added one to bring the screen below the plate, as suggested by Gerald Weber. But what GW really meant was to fix the 5E1 champ that fed the screen and plate off of the same node.

if the problem is at the screen or the screen resistor, the resistor may have saved the screen and the tube.

the amp had not lost volume or the underlying tone, and I doubt the power supply current went up because the fuse is only a half amp fuse and the amp idles and plays at 0.43 amps.

crossing my fingers
 




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