Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dpm309 on March 05, 2019, 04:37:04 pm
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Have a Vox AC30C2 with no sound. Both pilot lights light up and all of the heaters on the tubes are glowing. I am getting proper voltages on the tubes so the PT seems to be functioning properly. I am suspecting the OT but was wondering if there is anything else I should be looking at. Plate voltage (pin7) on the power tubes is 328VDC and 305VDC on Pin 9.
Thanks,
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What kind of test equipment do you have to check it with. A simple audio probe easily built with a couple parts will take you a long way into pinpointing the spot of signal loss. a guitar as your signal source, audio probe, and a working amp for the audio interface to your ears. About as simple as it gets but does work if no other equipment is available. Not recommended unless you are skilled working around the lethal voltages present in amp circuits.
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Zero sound? Bad speaker jack??
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Volume pot turned down? Just had to ask. :l2: :l2:
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I get absolutely no sound even with the volume turned all the way up. The speaker is hard wired into the amp. I have a listening amp/audio probe that I was planning on using to determine where the signal gets lost. Will also run a couple of tests on the OT.
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Cool. Sounds like you were looking more for some common problem with these amps the forum knew of vs more general troubleshooting help. Good luck with the probe. Keep us up to date with what you find. May be something we can use in the future.
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Check the cliffs for send/return, looks like in the schematic if they get boogard no sound.
make sure you got tube glow, the pre's use DC fil, the last on I worked on had toasted filament stuff on the DC side
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All the tubes are glowing. Cleaned the send/return jacks, tried the bypass switch and jumpered the loop jacks with no luck. Ran some simple output transformer tests which did not indicate any problems. I then ran a shorted winding test. The bulb lit up on the primary side (good) but did not light up on the secondary side. I ran this test with all of the leads disconnected. Will try the audio probe this afternoon when I get some time.
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Double checked the voltages on the preamp and power tubes - 3VDC for the preamps and 3.1VAC for the power tubes. I checked out the speakers using 9V battery and they are both working. Also plugged an extension cabinet in and did not get any sound. Using the audio probe, I get signal right up to the OT, but nothing after. Looks like the OT is fried.