Reverb transformer

[lowell]

I have a Boogie Mark I reissue here w/ dead reverb. I tried a working tank, checked continuity of cables, tube voltages of send/return tubes, the return circuit is working as I hear the tank when I tap on it. I tried a new send tube also, to no avail. The last component is the transformer. The primary DC resistance is reading 1.2k. Not sure if that sounds about right or not. The tank in here is a 10ohm input. Do I need to sub a transformer or can someone say what typical boogie primary DC resistance is?

[Enzo]

Play a signal into the amp. Is there signal coming out the secondary of the existing transformer? Is there signal at the plate of the drive tube? You could even connect the drive to a small speaker instead of the reverb pan to see if it is doing anything.

[lowell]

There is signal on the drive tube plate, none on the secondary, however as stated there is a "crash" when I knock on the tank. Gotta be the transformer right? I believe the secondary impedance for a replacement should be 8ohms, what about the primary?

[stokes]

Check the grounds on the cables.I dont know if the reissues have the same problem,but many of the MK's have issues with the ground at the chassis becoming corroded and losing contact.

[lowell]

checked continuity of cables per my initial post. Should've been more specific I guess, but yeah the grounds/hots are all indeed making connections.

[Enzo]

Don't even worry about impedance. All the little drive circuits are similar, so most anyone's little reverb tranny will work. Got a Fender one on hand? Clip it in place of the original.

As to gotta be the transformer, maybe, but for example if the jack for the cable is shorted, there will be no signal at teh secondary but the transformer would be OK.

[lowell]

Ok, boy this is really stumping me. I threw the new reverb transformer in there and still no reverb. Just to recap: I get the crash when I bang on the tank, I get a hum when I touch the return cable, there IS signal getting to the input of the tank as I see on my scope, there is NO signal on the reverb tank "out" jack even with no cable plugged in. Tank input is reading 1ohm DC, output is 212ohms DC. ??? My guess is the old reverb transformer fried this tank so I'm running in circles here. Unfortunately I don't have another tank at this time.

[lowell]

Ok I'm giving this back. I'm at a loss. Everything checks out w/ the reverb. The tank works, signal is getting to the tank but not through it. Any last minute ideas welcome.

[R.G.]

Ok I'm giving this back. I'm at a loss. Everything checks out w/ the reverb. The tank works, signal is getting to the tank but not through it. Any last minute ideas welcome.

Measure the DC resistance of the tank transducers. Sometimes these open up. If the input side transducer is open, you can have signal on the jack, but no drive to the spring.

Or just swap in a known-good tank.

If signal is getting to the tank input jack, as verified by scoping it, and whamming on the tank makes noise on the return, then the transducer must be bad, right?

[Albert Kreuzer]

Once (and only once) I had a case where the pan measured good DC-resistance-wise and still didn't work. So it can't hurt to try a different pan even if the first one measures OK.

[lowell]

Yeah I tried a known working tank, and tried the replacement tank on another amp too, both work. Oh well.. thanks guys.

[52 Bill]

Did you check the ground connection on the input of the tank? Mesa usually uses a grounded input jack on their tanks with and unshielded drive wire. If you sub a Fender type tank with an ungrounded input jack it will give symptoms that you describe.

[lowell]

Yeah I tried my rca cables that I have for testing and still no worky. Good advice though.

[lowell]

52 Bill and others, somewhere along the way I must've lost perspective. I had checked continuity of grounds at one point, but it must've been w/ the original tank. Turns out that that WAS the issue, after the bad reverb transformer was replaced that is. I couldn't get it to work w/ the new tank and w/ my test cables. And here's why, even though my test cables are shielded/grounded, the input still was not grounded because the rca jack at the chassis for the send is not grounded either. So I was basically running in circles. I added a ground to the send rca jack and it's all good. thanks again for the help.

[Ramsay]

Try resoldering the reverb tube socket conections!
Maybe a bad contact in a trail of the PCB cause the issue.