I have here a 1966 Danelectro 9100 Reverb Box a customer brought me. All original apart from one tube . I've never seen one before - they were never imported into the UK AFAIK, but I assume one of you in the US may know something about it... Fault symptom - the reverb doesn't work, although the rest of it does. I told the customer it should be an easy enough fix - how difficult can a reverb unit be? I assumed it would be very similar to a Fender one inside, and that it was probably a dead recovery tube or a broken transducer wire. But of course the dead part is the one thing that's critically different from a Fender - the reverb transducer. It looks like nothing I've ever seen in a reverb tank... a little package wrapped in cloth, possibly some sort of piezo/ceramic element, as it doesn't appear to be magnetic. The return one is simply producing no signal. It meters open-circuit - but then it would, if it's a piezo - and the send one does too, so I have no idea yet if that one's working or not either. Anyone know for sure what the transducer is or its spec? Is it replaceable with any common substitute? Is this a well-known fault? Thanks in advance.