# Classic 30 - some of the smoke got out



## buckaroobanzai (Feb 2, 2006)

Hi all amp gurus - I was jamming with friends a couple of days ago when my Classic 30 went quiet. I looked over and noticed to my horror that it was smoking around the midrange pot. I shut it off immediately. Also noticed that 2 of the EL84's lookad a lot blacker than I remember them looking ( matched quad of JJ's, about a year old). Went home with it ( smelled up the car pretty bad) and opened 'er up. Big resistor gone bye-bye.

Picture attached. I do some of my own repairs, and have built an Ax84 P1, but this is above my comfort zone. Also it's been my favorite gigging amp for a while and I hope it can be saved. Any and all advice gratefully received.


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## loudtubeamps (Feb 2, 2012)

I think it's time to take it in for a freshen up. It can be saved!


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## nonreverb (Sep 19, 2006)

Agreed, the circuit board on these amps is a complete PTA if serviced by the uninitiated. Better to let someone who's serviced one before have at it 



loudtubeamps said:


> I think it's time to take it in for a freshen up. It can be saved!


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## buckaroobanzai (Feb 2, 2006)

So, finally an update - it took me a while to source a new resistor for my Classic 30 - I didn't want to pay shipping to get a single resistor, and I couldnt find one locally. Had to wait until I was in Toronto picking some other stuff up. I found instructions ( with pictures!) on the interwebs. While the instructions suggested that the PCB be entirely removed to effect the repair, I decided to try a different approach. Since there was no visible damage to the solder connections on the board, I clipped off the dead resistor as close to the body as I could, and then formed loops out of the remaining ends. Then I placed the new resistor in position and hooked the new leads around the old ends. A couple of twists on the leads, and some careful soldering ( including heat-sinks on the stand-offs soldered to the PCB) and the new resistor was firmly in place. I powered it up without power tubes and measured the voltages - it all looked good, so I put a new quartet of JJ's in and tried it out. It's back , good as new. Hooray!

( I must confess that in my haste to get it back together and tested, I did not take pictures of the repair. Hopefully my description of what I did makes sense - )


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## greco (Jul 15, 2007)

WELL DONE!...Congrats !

Thanks for the update and the detailed description of the repair.

Cheers

Dave


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## Chito (Feb 17, 2006)

Congrats. I wish I could do things like what you did. If I had the same problem, it would've gone to nonreverb.


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## shoretyus (Jan 6, 2007)

Chito said:


> Congrats. I wish I could do things like what you did. If I had the same problem, it would've gone to nonreverb.


Amen..him and his soulmate Captain foldback are on speed dial.....


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## jb welder (Sep 14, 2010)

Good job. That seems to be a fairly common fault with those amps. When an EL84 goes bad and draws excess screen current, it can fry that resistor. So you have to stay on top of the condition of the power tubes. 
Ideally, the main B+ line should be fused. If you have to go through this again, you might consider installing one.
As far as the "short cut" on the repair job, I don't really consider it a problem due to the standoffs that resistor is mounted on, and the fact that you used heatsinks on them while you soldered in the resistor. You saved yourself a lot of time and other potential problems doing it without pulling the board and bending all those wire jumpers.
Just as long as you kept the new resistor off the circuit board so it doesn't burn next time.


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