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I just purchased an A100 from a church. It has been sitting in the fellowship building for a long time and I made them an offer of $100 and they took me up on it. Everything seems to be working fine except the reverb. I have an M100 that has the exact same amp and reverb unit. I switched the tubes out with no results. I then took the reverb unit itself out of the M100 and hooked it up to the A100. Still no results. Any suggestions???
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Check the wiring from the reverb amp output, to the reverb control, and then to the reverb speaker. Maybe a connection is broken along the way. The reverb didn't work on my A100 when I got it, there was a big empty hole where the reverb speaker was supposed to be 8)
And congratulations on a really sweet find!Tom in Tulsa
Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720 -
One basic diagnostic test to try with spring reverb problems is to shake the spring tank a little. If you hear clanging springs, the problem is on the drive side. If you hear nothing, the problem is on the recovery side. This assumes the tank itself is good, but I think you swapped them.
Also, test the grey molded RCA cables for continuity. They are known to fail.I'm David. 'Dave' is someone else's name.Comment
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RCA cables and the wiring from reverb amp to reverb control can easily enough be ohm'ed out for continuity.Comment
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All wiring checks out for continuity and still no reverb. Maybe a problem with the amp itself??Comment
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Did you try the 'shake' test?
Tom in Tulsa
Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720Comment
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I have to visit a studio soon with a non working A100 reverb and I deduced it is the output transformer that has failed. That one also has nothing on the output when the tank is shaken. We have found a replacement for me to fit.Hammond A100, M102, X5, XB3, XB5, TTR-100,
Lowrey DSO-1, H25-3, Yamaha E70, RA-100,
Farfisa Compact Duo MK2, Vox Continental 300,
Korg BX3 MK1, Leslie 145, 122.Comment
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I wouldn't immediately jump to the conclusion that it's a bad output transformer. For example, if it's the AO-44 reverb amp, it has a transistor first gain stage, and 1960s transistors can fail, as can the electrolytic coupling capacitors connected to them. Or it could be a bad tube.
Also, do test the output transducer in the reverb tank for continuity as well. These old tanks suffer less from open transducers than more recent production, but it can happen.I'm David. 'Dave' is someone else's name.Comment
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Thanks David. On my first visit I took a replacement transistor and replaced the electrolytics as well. I could not get continuity through the transformer windings although I did get a crackle through the speaker when I put my meter probes on the transformer wire solder joints. I did not think of doing the transducer check. It's a friend of a friend's studio and he wanted to see if I could fix it before trying a pro as I had done repairs on the organ before. -
Hi Dave, I was really talking to the OP here. A bad output transformer is not the first thing I'd think of in a no-signal situation. I'm not saying you didn't find one, but it's not common. -
Ah I see :-) I had recently diagnosed a dead OT on a two tube preamp so it seemed worth checking as nothing else seemed wrong with the amp! At least for the OP reverb amps pop up on ebay quite a lot.
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The rheostat easily gets dirty and develops "dead spots" - on my A-100 it was mostly all a "dead spot", actually. Try cleaning the rheostat thoroughly.Current organs: AV, M-3, A-100
Current Leslies: 22H, 122, 770Comment
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I had the same problem on mine a few years back. Cleaning the rheostat worked for me. Give it a shot and let us know.Comment
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Mine is also a sealed unit, try shorting together the two wires on the rheostat and see if you get any sound.Tom in Tulsa
Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720Comment
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