Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: AxeAmpTN on September 23, 2019, 11:00:03 am
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A customer brought in a 1980 Twin Reverb that he said had been giving him troubles, sometimes not even turning on. Initial test showed it to be working. Upon opening it up, I found the power switch had been replaced and sloppy soldering had previously left shorted pin connections on the first 6L6 socket. Since there had been obvious arcing, I replaced the socket. I cleaned up the bad soldering, including replacing the power switch. Also recapped since those were all original. Also replaced the missing pilot lamp.
Went to do the initial power up with no tubes, but nothing came on. I checked to make sure the fuse is good (check) and the switch is working (check), but there only a few millivolts are reading on all the secondary windings. I see nothing to indicate a shorted or otherwise damaged PT, especially since it worked when the customer brought it in.
Anyone experience this? Any insights or recommendations? Am I looking at a bad PT?
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Got 120v ***ACROSS*** the primary winding? If so, disconnect all secondary leads and recheck for proper voltage across each winding.
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Thanks for that reminder, sluckey. I checked the voltage across and sure enough it was millivolts. The only other thing in the circuit after the cord is the ground switch, which I moved to "off" then after 3 seconds, the pilot suddently came on. Now it works in all positions. I'm guessing it's not actually the ground switch (since I messed with it before, but actually something with the 39-year old power cord.
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And now that everything seems to be working right, I'm worried that my customer will get this back only to have problems. How likely is it that the ground switch is causing issues with power into the transformer? Any reason I can't remove the ground switch (since the amp already has a 3-prong cord)?
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The only other thing in the circuit after the cord is the ground switch,
There should also be a fuse and power switch.
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The only other thing in the circuit after the cord is the ground switch,
There should also be a fuse and power switch.
Yes, you're right, there is a fuse (which is good) and of course the power switch (also good). Guess I'm just saying the only thing I'm questioning is the integrity of the ground switch vs. that of the power cord.
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Test the cord and plug for continuity while moving the cord agound. Could be an intermittant break in one of the wires or the plug its self?