Ampeg GT10 reverb

[pontiacpete]

This reverb circuit is very strange to me. It has 43vdc on the input. Not knowing this, when I pulled the cables,the input cable shorted to the tank now there's no reverb.
This is what I've tried quite so far. Pulled Q3, Q4 and Q5 to check out of circuit and they tested good. But my tester, the "Peak Atlas DCA' is not always accurate, so I subbed in a BC184 for the BC169s (Q3 and Q5) and a TIP31 for Q4 (40625). This made no difference.
There is no sound of springs crash when banging on the tank. The input transducer has 24 ohms and the output one has 166ohms. Tried subbing in an 'EB.....' (original tank is the 'DB..'), still nothing.
Here are the voltages on these transistors
Q3 C 3.3vdc
B 1v
E .35v
Q4 C 41.8vdc
B 3.2v
E 2.6v
Q5 C 10.9vdc
B 1.3v
E .7v

Does anyone have an idea where to go from here?
Thanks

[52 Bill]

There is no sound of springs crash when banging on the tank.

If the return circuit is not working, there will not be any reverb. Start by checking the return circuit transistor and input cap.

You can take the reverb tank output and send it to another amp (signal tracer) to see if the drive circuit is working.

[J M Fahey]

Agree and suggest extra tests.
Each component pair means "the net joining them" including relevant component legs.

Inject some audio , through a .047 or .022 capacitor since all those points have some DC present , at:

* C19-C16
* C16-R27
* R27 - VR4 with VR4 set to 0
* R27 - VR4 with VR4 set to 10
* VR4 wiper with VR4 set to 10
* VR4 - C15
* C15 - R24
* C13 - R23
* J3 hot leg
* C13 - R47
* R47 - Reverb return RCA (I assume they use one)

Any and all of these, some louder, some softer, must be heard on the speaker.
When sound disappears or becomes mosquito/garbled, you found the problem area.
Test both ends of any track or wire involved innthe path, you may NOT have a "bad parts" īproblems, thatīs why I **HATE** shotgunning, but a *connection* one.
Your straight to +V short may very well have vaporized a track or wire and you will never catch that with a Peak/Atlas thingie.

Also check, with amp OFF and caps well discharged, that you measure 1k from Q4 collector to +43 line with reverb unplugged and some 24 ohm with it plugged; also that you measure some 166 ohm from R47btop to ground with reverb plugged in.

[pontiacpete]

Test both ends of any track or wire involved innthe path, you may NOT have a "bad parts" īproblems, thatīs why I **HATE** shotgunning, but a *connection* one.
Your straight to +V short may very well have vaporized a track or wire and you will never catch that with a Peak/Atlas thingie.

Found a broken solder pad from a trace on a leg of the Reverb pot. Thanks for the help with this!!