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arcanon1313
Silver Member
USA
414 Posts |
 Posted - 05/21/2006 : 13:44:39
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I just got an Ampeg VL-1002 100 watt all tube head from my boss. (I finally work in a music shop!) One problem...It doesn't work! It has no tubes, some parts have been "canibalized" (Bais switch EL-34 to 6550, Impedance three position knob switch 4-8-16 ohms, hum balance knob, 2 of 4 power tube sockets, possibly more that i can't see). And one small part of the PCB board that holds the power tube sockets along with 1 12AX7 socket is charred from some component getting fried. More than likely that is the only hard to come by part that I need to get it up and running. If ANYBODY knows how to fix tube amps, or knows someone that can fix, or help with schematics, or can possibly make me a new board PLEASE HELP! If I can fix it. I can keep it! Thanx in advance! |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 05/21/2006 : 14:26:42
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The schematic can be found on FreeInfoSociety.
You will need to start by replacing the missing parts. EL34 sockets are standard octal sockets and you should find out what tubes you need from the schematic. PCBs can normally be repaired without too much trouble. You may have to call Ampeg to get identical replacement switches.
A standard troubleshooting technique is to plug it in with no tubes (rectifier tubes need to stay in place). Measure the output voltage from the power supply and make sure it's ok (not that voltages from an unregulated power supply will typically be much higher than noted on the schematic when it is plugged in without any load).
Then plug in the output tubes, measure all DC voltages and verify they're within limits. Finally plug in input tubes and do the same thing. It's a divide and conquer approach that usually works well. When all DC voltages are stable and within limits you will need to calibrate the balance of the output valves and then you can test with an AC signal.
Sorry to say this but it is probably not an easy job. Why did the amp get cannibalised in the first place? Perhps there was a problem so nasty that the tech who originally worked on it couldn't find it and gave up? You could end up replacing the missing parts at high cost just to find out that you're troubleshooting that same difficult problem. |
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stahlhart
Platinum Member
1318 Posts |
Posted - 05/21/2006 : 15:07:19
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Sounds to me like someone who thought that they knew what they were doing, but didn't, attempted to modify the amp and turn it into something like a Marshall. The ensuing damage was probably caused by the ill-conceived modifications.
Since you have the schematic now (Ampegs often attach them right to the amplifier, on the shield plate that covers the chassis cavity -- both my old V-4B and my current GU-12 did/do), you could probably restore the damaged traces to the circuit board using point-to-point wiring on the underside. That's probably going to be the only way you'll be able to accomplish it, as getting a replacement circuit board alone is going to be virtually impossible unless you get extremely fortunate and find another "parts" amplifier you could salvage one from.
The schematic ought to be sufficient for you to restore the original board components, provided you aren't missing anything weird like tapped inductors for midrange tone control, photoresistor/lamp modules for tremolo, etc. Ampegs are probably the best amps out there for weird components like this, so be careful. But things like the resistors and capacitors you should be able to spec out correctly.
There are some forums around that are devoted to tube amplifier gear -- one that immediately comes to mind is http://www.firebottle.com/ampage, but I have yet to figure out how to register and participate on it (I can't find the link(s) on the page that take you to the registration)... if you can, please let me know.  Activity level there seems to be about the same as it is here, and there are some knowledgable people participating.
Here is some additional Ampeg information, though i'm not sure how many of the resources are still available for contact -- wouldn't hurt to try... if I remember correctly, I contacted the guy here from St. Louis a few years ago and got a replacement tremolo module for my GU-12 from him: http://users.aol.com/bluemuse/ampeg.html
C.K.
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Does Anybody know how to fix tube amps?
