sound city 50r mk 3 reverb tank

[pontiacpete]

Would anyone here happen to know what reverb tank is best for this amp?
Here's what the original looks like:

Servicing a Sound City 50R Amplifier

[Alex R]

Presumably you don't have the original to read the Accutronics code from. So...

Looks like the long (16.75") version, which gives us the first digit, either 4 or 9 (short or 9.25" is 1 or 8). 1 and 4 are 2-spring, 8 and 9 3-spring.

Very likely to be transformer-driven (though I don't see one in the pics), so now we have the next code element signifying lo-Z input, A. Codes B through to F are higher-impedance for solid state driven reverbs.

This is followed by the usual output impedance code, B. A is lower impedance, C higher.

Next digit is the decay time, can be 1, 2 or 3 according to taste and availability. Code 3 is positively oceanic, man.

Next element is a letter signifying which connector sheath is grounded to the tank chassis. Can't tell you which is right but if it's wrong (ie makes a hum loop or fails to ground the tank) you can mod it by disconnecting a sheath or adding a ground wire.

Penultimate digit is usually 1, signifying no locking device.

Final letter is intended orientation. Yours is vertical, connectors down, so code D. This one will make things a bit difficult for you, as all the readily-available transformer-coupled types are code B, meant for the usual cab-base scenario. If you have some old tanks hanging around or some other source of little springs, then I'd get a code B and add a couple more of those little springs to the top suspension points, or maybe just shorten the ones in there a little. Or maybe it will hang ok straight out of the box, you never know.

The standard old-style tube Fender 9AB2C1B should do the job if you can get it to hang right when on its side, which I think you will. Really anything that begins 4A or 9A will work ok with a transformer-coupled circuit, and it's a bonus if you can get a D or even a C suffix (C needs connectors on the up side but you could do that I guess).

There's some kind of a problem with Accutronics, it got sold out I think, and a lot of suppliers will now sell you a Belton alternative or Mojo-branded or something, but the codes still are meaningful. Just watch they sell you a low impedance input, like a speaker-type impedance, and the right length of tank.

(All that is AFAIK so please correct if anyone knows better, it's a good few years since I wrote all this in the back of my Allparts catalogue)

[pontiacpete]

It does have a transformer for the reverb. The one in that site is definitely a long tank. I have several tanks here. When I try the 9AB3C1B I get nothing out of it, no crash when tapped. I hook up an 8AB2A1B and I get the crashing noise when I knock on the tank but no reverb on the guitar.
I don't know what to make of this.
Thanks for the detailed explaination.
Could it be the output impedence is lower or higher than the 'B' type?

[Alex R]

Did you check the output coil on that 9AB3C1B, just measure the resistance across it?

[pontiacpete]

The output coil is good, 216ohms. It's a new tank, actually.

[Alex R]

That is strange, you should certainly get some response out of that output, whatever the impedance. Plug in your leads and check you still get the 216ohms inside the amp chassis? You can test the output coil in a rough and ready way by connecting it to a jack and plugging it into a guitar amp.

[pontiacpete]

That is strange, you should certainly get some response out of that output, whatever the impedance. Plug in your leads and check you still get the 216ohms inside the amp chassis? You can test the output coil in a rough and ready way by connecting it to a jack and plugging it into a guitar amp.

I don't think I understand this. I plugged into another amp from the output of the reverb transformer and got a lot of noise. What does that tell me?
I added a picture of the transformer and the 2 terminal strips that I believe is where the reverb should be connected.

[pontiacpete]

got it working with the 9AB3C1B. Had the hook up wrong. Now I need to find the best suited tank. This one doesn't respond that well. I have to turn it up a lot to get some reverb out of it. I will experiment with the other tanks that I have.
Thanks for the help!
pete

[Alex R]

That transformer should drive the 9AB tank ok.