Carvin MTS 3200 reverb mystery

[Randall]

Got this amp in wit a multitude of problems, got most of them sorted out, but the reverb does not work. While tracing the path I see a good strong signal on the driver plate as well as on the input jack, but nothing on the output jack. I inject a sine into the return wire and it shows up and is controlled by the volume pot. I swapped out another tank and the same thing, strange, then a second swap, still no reverb. Then I sent the output of the tank to another amp input, no guitar signal, but I do hear noise when I touch the springs. I go back and forth between my 3 available tanks with the same result, none will produce guitar reverb despite measuring a stong input signal at the tank inputs. I feel like I am in the twilight zone here, how am I getting the same result with my two tanks?

I just verified the 3 tanks with a known working amp, the Carvin tank did not work, and my two subs did work. What am I missing?

[alexradium]

the Carvin tank has high impedance,because its directly coupled to the plate of the driver triode,instead of a transformer like a Fender,its a pretty common failure in this amp,mine also did it.
Check out the code on the tank,for replacement

[g1]

And that 'high impedance' is probably much higher than you can commonly get anywhere. Carvin often used 9GB2C1B, which is around 8K input impedance, so would read around 700 ohms on your meter.
An E or F input impedance might work, but I'd still expect it to be quite weak.
What type tank did you try in there as a replacement?

[Randall]

AH, impedence was in the back of my mind, which I thought I was losing. I tried a tank from a Twin Reverb, a 4AB3C1B. Ther original is 9GB2C1B.

What I don't understand is, why did I get no signal feeding a known good tank from the Carvin reverb send to the tank reverbinput and from tank output into input of a test amp?

I just verified that I have 200 ohms on the output transducer and 735 ohms on the input, so shouldn't this be working? I only find new ones in the UK for about 3X what I am used to paying, so I don't want to just throw a new tank at it and hope it works.

[Enzo]

Did you try measuring the reverb pan resistances from the amp end of the cables? That is to say THROUGH the cables?

[Randall]

Good thinking. I just tried that and they are about the same through the amp cables and an extender cable.

This makes no sense to me.

[nickb]

What I don't understand is, why did I get no signal feeding a known good tank from the Carvin reverb send to the tank reverbinput and from tank output into input of a test amp?

I just verified that I have 200 ohms on the output transducer and 735 ohms on the input, so shouldn't this be working? I only find new ones in the UK for about 3X what I am used to paying, so I don't want to just throw a new tank at it and hope it works.

The 9GB is 8k. The 4AB is 8 ohms. That's 1000:1 or ~30:1 if you think about turns on the coil. The drive depends on turns x current, so if the current were same, you'd have 1/30 the drive with the 4AB and so hardly any output.

[Randall]

It was something in the cabling/ jacks. I resoldered the jack wires, cleaned them and cable conncetors, and reseated the other end of the wires where the fit directly to the board via push on connectors. The output jack is a little finicky, but at least I can stop worrying about why both transducers measured correctly and both the send and return circuits were working, but no reverb. The fellow will bbe happy. Thanks for steering me right yet once again!

[moshpit903]

I've had 2 of those and really liked them,seemed very solid,but like everything they break down..imo they are really good for the prices they sell at..both mine had Sovtek 5881's in them and really liked them.
Now biasing them was a different story,but not that hard to do.