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Peavey classic vtr problems
Hello Guys, I'm new here so please excuse any mistakes or overlong meanderings!
To cut a long story short...about a year ago I bought an old Peavey Classic 2x12 VTR on ebay. Looked like it had the original 6L6 tubes from 1981 still fitted!... so I swapped them out with Russian Electro Harmonix ones. Volume levels seemed to still be up and down, so it was stripped down and the main PCB removed. As suspected... full of dry joints, plus on the valve bases too - all resoldered and cleaned up etc. I noted that one of the 5885 cathode drivers and it's protect transistor on the board had been swapped out with TIP41 AND BC182....still it was working perfectly now, and I had no schematic so it was left at that. I did a dozen or more gigs with the combo, which by the way produces a great satisfying articulate yet creamy tone...one of the best amps I've had in fact.
And so the trouble starts....during a rehearsal...a loud 'pop' then dead (at least it wasn't during a gig...). Now a small weedy distorted output.
I took it to work, where I have a bench, good light, tools, test gear (I'm in electronics as it happens).
The main HT fuse had blown, (1 amp fast). TIP41 and it's protect transistor both short....hmmm.
I contacted Peavey U.K. who kindly sent me a PDF schematic and for £10, two new drivers and two protect transistors. The T0-220 drivers were MJE15032G, 250v devices...better than the 150v originals, the two protect transistors MPS6531's. All surrounding resistors checked, an a few old electolytics swapped out on the board for good measure. Main board reseated with all it's connectors, and the fuse replaced.
So, switch on....500v sitting on the anodes and +80v on the MJE collectors/6L6 cathodes. +/- 15v rails good...a little white noise from the speakers...and, yes the amp is working again! I ran a CD through it for half an hour at high volume to prove the point, then reassembled.
This was a week ago....today with the amp at home (and no schematic - it's at work and it's Easter) I tried the combo with a guitar.
At switch on there was a slight frying noise....it worked for a couple of mins then 'pop' and dead again!!! F**K!
I opened up the chassis - 1 amp fuse open cricuit again. One MPS transistor short and the accociated MJE driver leaky base/emitter...although I need to pull them out for further checks...this will be back at work now.
Somthing strange is happening on that half of the output stage...overvolting? I'm just wondering if it's on of the (new) valves going internal short.
All this is on the same side that the TIP41 was originaly replaced on...a bad omen for s/c output transformer?? Maybe somthing in the drive circuitry between the op amp and base of the MJE....I hope.
I'll post more later, after more probing....but has anyone come upon a similar fault on one of the Peavey VTR combos?
If so...I need help! The problem is I don't feel I can trust this amp now....
Thanks for reading, Steve.
To cut a long story short...about a year ago I bought an old Peavey Classic 2x12 VTR on ebay. Looked like it had the original 6L6 tubes from 1981 still fitted!... so I swapped them out with Russian Electro Harmonix ones. Volume levels seemed to still be up and down, so it was stripped down and the main PCB removed. As suspected... full of dry joints, plus on the valve bases too - all resoldered and cleaned up etc. I noted that one of the 5885 cathode drivers and it's protect transistor on the board had been swapped out with TIP41 AND BC182....still it was working perfectly now, and I had no schematic so it was left at that. I did a dozen or more gigs with the combo, which by the way produces a great satisfying articulate yet creamy tone...one of the best amps I've had in fact.
And so the trouble starts....during a rehearsal...a loud 'pop' then dead (at least it wasn't during a gig...). Now a small weedy distorted output.
I took it to work, where I have a bench, good light, tools, test gear (I'm in electronics as it happens).
The main HT fuse had blown, (1 amp fast). TIP41 and it's protect transistor both short....hmmm.
I contacted Peavey U.K. who kindly sent me a PDF schematic and for £10, two new drivers and two protect transistors. The T0-220 drivers were MJE15032G, 250v devices...better than the 150v originals, the two protect transistors MPS6531's. All surrounding resistors checked, an a few old electolytics swapped out on the board for good measure. Main board reseated with all it's connectors, and the fuse replaced.
So, switch on....500v sitting on the anodes and +80v on the MJE collectors/6L6 cathodes. +/- 15v rails good...a little white noise from the speakers...and, yes the amp is working again! I ran a CD through it for half an hour at high volume to prove the point, then reassembled.
This was a week ago....today with the amp at home (and no schematic - it's at work and it's Easter) I tried the combo with a guitar.
At switch on there was a slight frying noise....it worked for a couple of mins then 'pop' and dead again!!! F**K!
I opened up the chassis - 1 amp fuse open cricuit again. One MPS transistor short and the accociated MJE driver leaky base/emitter...although I need to pull them out for further checks...this will be back at work now.
Somthing strange is happening on that half of the output stage...overvolting? I'm just wondering if it's on of the (new) valves going internal short.
All this is on the same side that the TIP41 was originaly replaced on...a bad omen for s/c output transformer?? Maybe somthing in the drive circuitry between the op amp and base of the MJE....I hope.
I'll post more later, after more probing....but has anyone come upon a similar fault on one of the Peavey VTR combos?
If so...I need help! The problem is I don't feel I can trust this amp now....
Thanks for reading, Steve.
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