Radioshack Realistic Pro Verb

[Passaloutre]

Ancient transistorized spring reverb unit here. I picked this up at an antique store. Can't find a schematic anywhere. I get a nicely boosted dry signal through it (reminds me of Echoplex preamp), and a very weak reverb signal with the knob all the way up.

I've attached some photos of the interiors. It's clearly been modified, three transistors have been changed (solder-spliced to the dead legs of the originals), and one (presumably original) four-leg metal-can transistor that I can't identify or figure out the pinout. The replacement transistors say "CBS 1232" on them, but I can't find a datasheet for that part, and I can't make out any markings on the four-leg guy.

The filter capacitors also appear unoriginal and the values seem to have been chosen at random as far as I can tell.

Anyone care to make sense of my schematic? I've double checked it with my meter, but I'm sure there remain errors. What's the deal with the four leg transistor?

More photos of the guts are here: https://imgur.com/a/527Kr9i

It has a tiny tank inside, but I don't know how to measure the coils. I'd like to get it back to it's original shape, but if not I suppose I can build a different reverb circuit into the box, maybe with something like this: https://www.tubesandmore.com/product...mc2bf-2-spring










EDIT: looking through the JEDEC transistor package documentation, the metal can thing appears to be a TO-7 transistor, one of the legs would be a shield presumably.

[Passaloutre]

Here's a crop of the area around the 4-leg transistor: https://i.imgur.com/u4Jxd8P.jpg

• The red wires in the background are a ground bus
• The red wire in the foreground (at the junction of the 470 and 10 ohm resistors) is the "B" power node.
• The white wire with black stripe goes to the input of the reverb tank.
• I can confirm there are no connections on the back of the board, so everything should be visible here.

[The Dude]

Did you check that 25uF coupling cap? Also, if you could label transistor voltages on the schematic, it might tell us something.

[dmeek]

The four leg transistor is probably the same pinout as these

[g1]

It's odd that they would have the 2 resistors in parallel like that (22K and 68K). Unless someone replaced that can and had to tweak the bias, or if that's how they tweaked for the cans at the factory. If germanium I guess they would be finicky.

Can you see in the tank at all? Maybe post some pictures? If it's piezo type transducers you might not want to waste much time on it.