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Topic: Old Session 400 "Nightmare on Wilburn St" |
Ken Fox
From:
Nashville GA USA
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Posted 18 Sep 2012 4:28 am |
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Got this in from a Forum member for a mod. My policy has been no non-working amps. Well this one worked, sort of.
It had been butchered by some repair shop or individual in the past. The power amp board had one of the 4 stand-offs still holding a little, 2 broken off and 1 screw put in to hold another corner. The board was sitting on a piece of styrofoam to boot! Power amp had 0.75 volts of DC present on speaker outs (a bad thing). Not to mention that FedEx managed to damage it cosmetically, due to poor packing by the FedEx store.
Also it was held in the cabinet with only two of the cage nuts. The chassis was bent and deformed where the others were pulled out with some great force. A little body and fender work and I straightened all 4 mounitng holes as well as installed two Peavey 10-24 cage nuts for the missing ones, I installed 6-32" stainless steel stand-offs for the power amp board.
Got the power amp modded and checked, still DC on the outputs. Replaced two noisy transistors on the power board and pulled the output transistors to test. 3 were original RCA and 3 were Peavey replacement parts. Ah, the power amp had been worked on before! All tested good but one of the chassis mounted T-03 transistor sockets was broken (one of the leads was held on with some shrink tubing by the previous amp butcher). Replaced that and put in 6 all new plastic style T-03 insulators. DC offset was gone!
On to the preamp, it had noise in it upon arrival as well. Modded it and then spent about 3 hours chasing a ghost noise. Several transistors, capacitors and resistors finally resolved that. Cleaned up poor solder joints on the pots (a common problem on the older amps). This was a 1974 amp, one of the earlier ones with the metal faceplace.
Well, the cost of my labor and mod would have exceeded the value of the amp. So as in the past we made another contribution to salvation of another old amp.
It sounds awesome! However this will be my last one that I repair, period. I just do not want to chase ghost noises in these old amps anymore. Spent too much time doing that in the past.
Here it is all modded and repaired:
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Ken Fox
From:
Nashville GA USA
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Posted 18 Sep 2012 4:58 am
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Also the power transformer was replaced in the past. One of the Molex connectors from it to the power amp board was gone, wires soldered to the terminals. I replaced the missing Molex plug and cleaned up the solding mess on the Molex pins as well. Diode on the epower board had been burned out and replaced, cleaned up the burned area as much as possible.
All in all folks, you might want to take a good look at the inside of an older amp, if you are buying one. There can be a real can of worms in there sometimes.
Last edited by Ken Fox on 21 Sep 2012 4:58 am; edited 1 time in total |
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Ray Anderson
From:
Jenkins, Kentucky USA
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Posted 18 Sep 2012 5:06 am
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Sure good to know that there are people out there with heart and integrity, a quickly fading attribute I might add.  |
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Ken Fox
From:
Nashville GA USA
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Posted 18 Sep 2012 5:16 am
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Well, I have done it for a long time. Guess I am just ready to retire at the end of this year and pursue camping, music, etc! After the house fire and 7 months of work to get the home back I decided to lighten my load. Now all I do is old vintage tube amp repair, mod a few working Peavey amps and sell some nice mod kits for the amps.
I decided to do no more solid state amp repair as well as work on Webb or Evans amps. Derrel Stephens does a great job on Evans amps. As far as Webb, who knows. I repaired about 20 for Tom B in the past. Not sure if he has a west coast tech, but I bet he does by now. You can't beat these two guys, they are great. |
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