Weak Reverb

[ricach]

Blackface ProReverb. Yes, I did all the obvious checks. What I'm scoping is lots of signal entering the tank and unmeasureable signal leaving the tank. (measured from inside the tank) There is a signal there, somewhere, because the recovery tube amplifies it to an audible (and measurable) level. But it's about a tenth the level hitting the tank. Hence I've got reverb, but weak.

My guess it has to be the tank, but I don't have an identical tank to swap out. I did try a gibson tank, and was getting the exact same readings, but I think that was due to a severe impedance mismatch since they are completly different tanks.

Before ordering a new tank, I want to double check that I haven't missed a trick. Any ideas?

UPDATE: Thought I'd check the resistance of the input and output and now suspect this is not the right tank. (So much for checking all the obvious things first) I'm getting about 165/170 in/output. Checking the resistance of the xformer and its at 2ohms which tells me this tank was never the right one. Although my friend insisted it sounded great in the past, I'm doubting that now.

I'm guessing the tank I need is a 4AB3C1B. Can anybody verify this?

[izzybell2810]

The amp should have 4AB3C1B tank as you thought. It has input impedance of 8 ohms and an output impedance of 2250 ohms. it's an input insulated output grounded type. What's the number of the pan fitted?

[Chuck H]

The output of the tank SHOULD be truely tiny. The input needs to be substantial to shake the springs. But the output can only be what the tiny magnets in the recovery transducers make. Have you tried swapping out the reverb recovery tube? That tube is responsible for re-amplifying the signal from the tank.

Chuck

[ricach]

There is no model number on the tank. But it does have an accutronic label inside.

Yes, I did replace out the recovery tube and checked all the voltages against the fender schematic. Talking with my friend, he insists the reverb was much stronger and can pinpoint the gig when he noticed it had become almost nonexistant. Although I know for sure its the wrong tank, I'm thinking there is still more to the problem. Or, this tank is going south and needs to be replaced anyway.

[Chuck H]

Well then... If the voltages check out, the electronic componants check out and you know that it worked better once upon a time, that only leaves the tank and the transformer. I'd bet on the tank. You can check the transformer by putting an 8 ohm resistor across the secondary and measuring it's output. I've never done it but with the amp up loud you should probably see about half a watt.

The above tank ID is correct.

Chuck