Gregory ADD-VERB

The Gregory "ADD-VERB" is a standalone reverb unit, probably from the 1960s. Very simple inside. The whole thing is build point-to-point using small tagboard. The reverb driver section should look familiar to fuzz effect fans. The top input jack is labelled "MIKE" - yes, spelled that way - and the other two are labelled "INSTRUMENTS."

The reverb input transformer is the collector load for the second transistor. This is an unusual arrangement, and surprised me because the second transistor was very small. Fortunately I had traced the circuit before I started messing with the reverb connections. It would have been very easy to wrongly assume that the RCA shield went to ground, when it fact it is connected to +30V above ground.

The original input transformer was broken beyond repair. One of the wires was completely ripped out. I was able to substitute a 9FB2A1C. I simply figured the input transformer must have a fairly high resistance to work correctly like this, and the "F" indicates the highest input impedance. Perhaps I am wrong about that, but the 9FB tank did work pretty well, so I didn't experiment further.

The output is phase inverted with respect to the input, and fairly high impedance due to the common emitter configuration and the 10kΩ collector resistor. The next stage needs an input impedance >100kΩ.