My reverb holiday didn’t last long, as I feared. The tank still echoes when struck, but no useful amount of organ sound gets into it, so I assume it is the drive transducer that has failed.
I replaced the valves - no change.
So, it looks like I have some homework to do.
I have reviewed the above information kindly provided, and chased those links.
Option 1: Repair the transducer? - no info around on this
Option 2: Replace the transducer? Apparently these were basically ceramic phono stylus transducers that haven’t been available since the 1970s, so that’s probably not going to happen.
Option 3: modify the current circuitry to drive a new-style reverb tank, as favoured above by the cognoscenti. The current piezo transducers apparently are high impedance (can’t find much data on exact numbers) while modern reverb tank systems vary from about 8 to 2000 ohms.https://www.tubesandmore.com/tech-corne ... d-compared
To modify the circuit, there are several possibilities.
Hugh favours re-wiring the valve circuit along the lines of a Fender amp reverb driver.
Dave favours adding a MOSFET to the drive valve - that Rod Elliot article explains the context http://sound.whsites.net/project167.htm
Will suggests using a transformer and replacing the type of valve to ECC82 to drive the highest impedance tank available (which appears to be around 1.5kohm)
The problem with all of those could be that there won’t be enough current available from the 210 volt winding on the main TX to power the new circuitry, but this could be improved by adding a diode bridge to replace the half-wave rectification that exists at present.
Schematic againhttp://www.adambaby.com/tempdownloadfil ... mboPSU.pdf
There is a big Rod Elliot article that covers a lot of this including transformer drive options and recovery circuits, that I am attempting to get my head around…http://sound.whsites.net/articles/reverb.htm
Phew! - who knew there was so much to consider when replacing a little ol reverb tank!