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Late December a Magnatone Stereo Twilighter amp came in from our rental inventor (CenterStaging, LLC Burbank, CA) with loud hum. I hadn’t had one of these opened up before, so after verifying the symptoms, which at first didn’t occur until I patched into the Hi gain input, then the loud hum was hostile. I pulled the chassis out and moved it to my service cradle, after taking a series of photos of the insides for reference. Then took photos of the chassis assy inside and out.
I found the speaker baffle was not secure at the top, moving a good inch and a half. I had to remove the Model plate at the top of the cabinet, which then exposed the 1.5” long drywall screws, finding they were stripped out. Replaced those with #10 x 1.5” truss head screws, now tight again. Put the logo plate back into place.
I looked at the solder joints of the preamp tubes on the PCB, seeing Lead-Free solder, and they were all very crusty in appearance. When I powered it up again to start chasing down the problems, I found a bad Bass Control, where touching the outside wires caused a lot of noise, so pulled it out, pulled the cover off the pot, cleaned/lubed the contacts, and tightened up the rivet that attaches the solder terminal to the wafer board/contact of that terminal. Put it back in, tried again. No more issues with that control, but found the problem was still there. After removing the tube shields, I found one of the ECC82/12AU7’s broken, and replaced that. Still had the loud hum. I had removed the Reverb assy and it was connected to the chassis on the service cradle. Turning up the Reverb control at all yielded the main source of hum. Found the tube associated with that (V4), and de-soldered the pins, and re-soldered with fresh Lead-Free solder. That now looked proper without that crusty appearance I saw on the other tubes on the PCB.
Powered back up, seemed ok, until I tapped on the PCB at that tube with a chop stick, and the horrendous noise was back. I replaced that tube, which now seemed to cure that problem. Prodded the three wires from the reverb control where they’re soldered into the PCB adjacent to V4, and those connections weren’t solid. Re-soldered those, and finally had a solid amp that I couldn’t cause any more noise.
Put the amp back together, and finally have a solid amp.
I had copied the schematics that LarBal had posted in his thread of 02/25/2021 on the Stereo Twilighter amp
https://music-electronics-forum.com/...reo-twilighter
schematic: Magnatone St Twilighter schematic rev 3 20150609.pdf
Very cool sounding amp!!!
I found the speaker baffle was not secure at the top, moving a good inch and a half. I had to remove the Model plate at the top of the cabinet, which then exposed the 1.5” long drywall screws, finding they were stripped out. Replaced those with #10 x 1.5” truss head screws, now tight again. Put the logo plate back into place.
I looked at the solder joints of the preamp tubes on the PCB, seeing Lead-Free solder, and they were all very crusty in appearance. When I powered it up again to start chasing down the problems, I found a bad Bass Control, where touching the outside wires caused a lot of noise, so pulled it out, pulled the cover off the pot, cleaned/lubed the contacts, and tightened up the rivet that attaches the solder terminal to the wafer board/contact of that terminal. Put it back in, tried again. No more issues with that control, but found the problem was still there. After removing the tube shields, I found one of the ECC82/12AU7’s broken, and replaced that. Still had the loud hum. I had removed the Reverb assy and it was connected to the chassis on the service cradle. Turning up the Reverb control at all yielded the main source of hum. Found the tube associated with that (V4), and de-soldered the pins, and re-soldered with fresh Lead-Free solder. That now looked proper without that crusty appearance I saw on the other tubes on the PCB.
Powered back up, seemed ok, until I tapped on the PCB at that tube with a chop stick, and the horrendous noise was back. I replaced that tube, which now seemed to cure that problem. Prodded the three wires from the reverb control where they’re soldered into the PCB adjacent to V4, and those connections weren’t solid. Re-soldered those, and finally had a solid amp that I couldn’t cause any more noise.
Put the amp back together, and finally have a solid amp.
I had copied the schematics that LarBal had posted in his thread of 02/25/2021 on the Stereo Twilighter amp
https://music-electronics-forum.com/...reo-twilighter
schematic: Magnatone St Twilighter schematic rev 3 20150609.pdf
Very cool sounding amp!!!
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