Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JaycetheOwl on December 27, 2015, 02:36:01 pm
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I have a Vox AC15CC and recently my reverb has stopped working all together.
I was bringing it to a gig and two things happened that might have caused it.
1. When it was in my car, at one point it fell over pretty hard during a turn.
2. When I first turned my amp on at the gig, it did not work, upon further inspection I found that the ground wire on my speaker terminal had come loose. Is it possible that because of this I possibly hurt the circuit inside the reverb tank?
I have the accutronics reverb tank, the replacement one.
I made sure the rca cables are in place, I also opened up the back panel just to make sure nothing was apparently amiss (I did at one point have to replace the reverb pot, so I wanted to make sure the solder joints were good, which they are).
Any thoughts? I'm hoping I just need to replace the Tank and nothing more.
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A little further non-technical test:
When I turn the amp on and uplug the rca cables, I do get noise when I touch either end of the rca cables, and I do get reverb noise if I plug them in, then rattle the reverb tank.
Still no reverb with guitar.
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I don't think the speaker wire has anything to do with the problem. Could be a bad tube though. To start try swapping V3 with a known good 12AX7. Check to make sure V3 is seated properly in the socket. Reverb tanks are pretty rugged but you could pull it and inspect it physically to make certain the springs or any other parts are not broken. I dropped one on the floor from table height once and it didn't do a thing to it. Works fine. But I know tubes can get damaged from shock.
Is everything else working on the amp? Here's some info on reverb tanks for you to look at. https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared (https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared)
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AC15CC
I went fishing for a schemo, but all I found were comments like "the Chinese didn't include one"
If you hear the springs and it makes noise touching the rca's, I'd look for broke/cracked traces, solder connections.
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It can also be: Inside the reverb can, from the chassis-mount RCA jacks to the coils run two teensy thin wires. They can break. They can be resoldered. However it is rather delicate to do and frankly I would not recommend it as a first thing you do in case you are a soldering newb. I've fixed a dozen or more over the years. On a few, one coil was indeed open.
If you have an ohmmeter, you can also test for coil continuity at both ends. If you have it, your tank is tanking properly and you don't have to do the above. I don't know what the plug config is on your amp, but in Fender we would have two male RCA cables leading to the reverb can and one could measure right from those. If it's good, you're done and don't have to take it apart.
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AC15CC
I went fishing for a schemo, but all I found were comments like "the Chinese didn't include one"
If you hear the springs and it makes noise touching the rca's, I'd look for broke/cracked traces, solder connections.
I also could not find a schematic :/
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I don't think the speaker wire has anything to do with the problem. Could be a bad tube though. To start try swapping V3 with a known good 12AX7. Check to make sure V3 is seated properly in the socket. Reverb tanks are pretty rugged but you could pull it and inspect it physically to make certain the springs or any other parts are not broken. I dropped one on the floor from table height once and it didn't do a thing to it. Works fine. But I know tubes can get damaged from shock.
Is everything else working on the amp? Here's some info on reverb tanks for you to look at. https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared (https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared)
The Vox AC15CC is solid state reverb, I don't have a V3.
I did open up the can, and couldn't discern anything to be wrong.
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It can also be: Inside the reverb can, from the chassis-mount RCA jacks to the coils run two teensy thin wires. They can break. They can be resoldered. However it is rather delicate to do and frankly I would not recommend it as a first thing you do in case you are a soldering newb. I've fixed a dozen or more over the years. On a few, one coil was indeed open.
If you have an ohmmeter, you can also test for coil continuity at both ends. If you have it, your tank is tanking properly and you don't have to do the above. I don't know what the plug config is on your amp, but in Fender we would have two male RCA cables leading to the reverb can and one could measure right from those. If it's good, you're done and don't have to take it apart.
I'm gonna go pick up an Ohmmeter today.
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this might be your schematic then looks like op amps in place of tubes http://www.guitarnewsdaily.com/wp-content/uploads/guitarpug/2008/06/ac15cc1_schematic_only.pdf (http://www.guitarnewsdaily.com/wp-content/uploads/guitarpug/2008/06/ac15cc1_schematic_only.pdf)
maybe check to make sure connector 3 (tcn 3) is secure and making good contact. check all the connectors and make sure they are making good contact - with power off then try the amp.
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Before the reverb stopped working, did it work without a footswitch? Could be a problem with the reverb part of the foot switch. Did you replace the pot with a pot of the same value? It would be hard to suspect a bad
mix pot if you just replaced it. But, it could be a bad connection to the pot. Also, which accutronics reverb pan did you use, assuming you replaced the original reverb pan. And why did you replace the reverb pan to begin with? Do you still have the original reverb pan?
Just for general checking - I'd check to make sure I had +/- 30v and +/- 15 volts which goes to IC1 and IC2 and IC3 respectively.
I also think I would reflow the solder joints on the mix pot to make sure they have good conductivity. A picture of that little board would be nice showing the mix pot pads.