Session 400 Reverb issue

Tommy Mc · From: Middlesex VT

I'm having some trouble with the reverb in my Session 400 and hope the collective mind here can point me towards a cure.
I've checked the cables and cleaned the RCA connections. The cable input and output are connected to the correct places. I can hear the springs crashing around through the speaker. In fact, they seem to be super sensitive. But with the steel hooked up, there's no "reverberation" effect, no matter how high I turn it up...just some background spring noise.

To troubleshoot, I've tried:
1. A different spare tank...no improvement
2. The tank from my Deluxe Reverb...no improvement
3. Connected the Peavey tank and cables to the Deluxe Reverb. Played through the DR and the Peavey tank worked fine.

So it would appear that my reverb tanks are functional. The Reverb circuit in the Session seems to be active, in that I can hear the springs crashing around and the level control turns it up and down. But there is no actual effect on the instrument. Thinking it through conceptually, it seems that I have reverb "output" but no "input". Any ideas what to check next?
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1980 MSA Vintage XL S-10, 1975 Session 400
1972 Dobro model 66s
Derby SD-10
Tom McDonough

Stephen Cowell · From: Round Rock, Texas, USA

Your reverb drive signal is missing. Make sure you haven't swapped the in and outs to the tank. You've tried another tank... this points to the tank being OK.

You can set your voltmeter to AC volts and look for a reverb drive signal by unplugging the drive (low impedance?) side and measuring at the plug with signal. No AC volts? Trace it back. Most reverb circuits switch off the recovery, not the drive... not sure about yours. Divide and conquer! You should see increasing AC volts as you proceed through the circuit.
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Tommy Mc · From: Middlesex VT

Thanks. I understand the concept, but not the exact process of which you speak. I did check and clean the connectors inside the amp and check for continuity. I can check for bad solder joints, but following a circuit is probably beyond my skill level. I guess I'll be using my reverb stomp box....
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1980 MSA Vintage XL S-10, 1975 Session 400
1972 Dobro model 66s
Derby SD-10
Tom McDonough

George Biner · From: Los Angeles, CA

Sounds like the tank is not getting signal from the amp. One thing you can do is open it up and wiggle the connectors and see if that makes a difference.

Beyond that, the signal needs to be traced because it's probably a bad component or open solder joint somewhere in the 48 year old amp. I am in LA very far from beautiful Vermont, else I would offer to fix it.
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Electrical engineer / amp tech in West Los Angeles -- I fix Peaveys
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