For all early 4100 / 4212 owners.

[digi2t]

Hi all. More bug fixes for the early versions of the Tourmaster (combo, or head only).

Last week, the treble pot on my second overdrive channel went wonky. As I would raise the treble level, the volume level would diminish. At max, the channel was completely mute. Figures it had to be the lower row, meaning that it would be double the work to get at it. Anywho, going over the schematic, along with some testing, revealed that the pot had a short to ground, between the 2 and 3 pins. First time I've ever encountered this. Probably a factory defect from the Alpha plant that finally reared it's ugly head. New pot fixed the problem.

While I was in there, my eyes noticed that something didn't jive between the schematic or board , and the "classic/modern" switch wiring for both overdrive channels. Further investigation revealed that they were connected backwards at the factory. Flipping the switches isn't really an option since the chassis holes are punched with the alignment tabs, so the wires had to be resoldered to the opposite poles. Easy test to see if your switches are backwards; flip between "classic" and "modern". If the percived sound level is higher in the "modern" mode, they're backwards. If you under take this work yourself, desolder the outermost wire (there's only two, leave the middle one in place), and resolder it to the opposite pole. You should be able to fish the switches out to do this without having to do any other major work. Maybe clip a tye-wrap here or there.

AS ALWAYS, USE EXTREME CAUTION WHEN WORKING INSIDE TUBE AMPLIFIERS. THERE ARE LETHAL VOLTAGES INVOLVED. IF YOU DON'T KNOW WHAT YOU ARE DOING, SEEK QUALIFIED HELP.

 

[davenz]

Thanks very much for this. It sounds very familiar. I have an early Tourmaster 4100 with similar symptoms.

The mid/bass frequencies on OD2 disappeared entirely and those knobs do precisely nothing now. The treble knob now acts as a volume (for the remaining treble frequencies), but it's not backwards as you describe. With the treble turned off there is no volume and as it's turned up I get more volume, but it's all very thin sounding.

I've been measuring pot resistances to try and find if one of them is shorting but have found no culprits so far.

I'd had these symptoms come and go a few times on OD2 (but failing much more that it's working), but recently something really weird happened. OD2 started working normally and the exact same problem occurred on OD1. No bass/mids and the treble knob acts like a volume. The only significant things I've done that could have caused some change is I removed the Clean2/OD2 EQ board from the chassis (still connected, just removed so I could get at the pots better and see their values). I also used some contact cleaner on the OD1/OD2 pots, but that's all I've done.

Based on your experiences do you have any tips for what might be causing this?
Also you mentioned that you have a schematic. Would you mind sharing that with me? Otherwise my next step is to map out the EQ boards myself. I tried asking Egnater Support for a schematic, but they wouldn't give me one. Any help much appreciated!

 

[digi2t]

I have schematics. Just note that that the page that covers the channel switching doesn't apply. It must have been a preliminary schematic, but Egnater went with a proprietary system instead of MIDI. The amp sections and power section drawings are correct though. Maybe some minor differences here and there, but accurate enough for troubleshooting.

https://drive.google.com/open?id=0B1N9M_iu6iFJZFJsaWZBdjMwU28

One thing I highly recommend is reflowing ALL the solder points on both pot board. This alone solved many of the intermittent control problems I had on all channels. I don't think that a jig was used to keep all the pots perfectly aligned when they were installed at the factory. As such, any slight misalignment get translated into stress on the solder joints when the boards were mounted into the chassis. A good test to see if it's a solder joint problem is simply loosening the nuts on the suspect pots to see if they start working properly. You might have to jiggle them a bit as well. If the pot works intermittently as you jiggle and turn it, then the solder joints might be suspect.

AS ALWAYS, USE EXTREME CAUTION WHEN WORKING INSIDE TUBE AMPLIFIERS. THERE ARE LETHAL VOLTAGES INVOLVED. IF YOU DON'T KNOW WHAT YOU ARE DOING, SEEK QUALIFIED HELP.

 

[davenz]

Thanks very much, I really appreciate the help.
Reflowing the EQ boards sounds like a good idea because it would be nice to get the amp to the point where I trust it for live use again.