prosonic reverb weak

[daz]

Wondering if anyone might have some advice here. it's a fender prosonic with reverb which on 10 sounds more like 2. The footswitch jack is fine, IE: The shorting tabs are shorted and reverb stops altogether when separating the shorting contacts. Have cleaned them well but no joy. Tried replacing both reverb tubes, V4 and 5. It's not the verb pot. Tried 2 different reverb pans and different cables. Voltages at the plates are normal and i can't seem to find any bad components. Touching the secondary side plug yields a good strong buzz. any other ideas?

[52 Bill]

Touching the secondary side plug yields a good strong buzz. any other ideas?

Wrong tank, tank plugged in backwards, bad driver transformer.

If you hook a small speaker to the drive transformer output do you hear a signal?

[daz]

Wrong tank, tank plugged in backwards, bad driver transformer.

If you hook a small speaker to the drive transformer output do you hear a signal?

I tired several tanks and plugged them in both ways to find the right way. So plugged in correctly and with different tanks, same result. I haven't tried that speaker trick tho. That would just tell me whether it's a issue before or after the pan, right? And i already think it's before because you can get loud noise moving the pan so i think the recovery circuit is fine.

[52 Bill]

I haven't tried that speaker trick tho. That would just tell me whether it's a issue before or after the pan, right? And i already think it's before because you can get loud noise moving the pan so i think the recovery circuit is fine.

Yes, the recovery circuit seems to be fine, but if the drive is weak you could have a problem. Also what tanks have you tried it with? If the input transducer is not an 8 ohm coil, you will have weak reverb.

[daz]

Yes, the recovery circuit seems to be fine, but if the drive is weak you could have a problem. Also what tanks have you tried it with? If the input transducer is not an 8 ohm coil, you will have weak reverb.

One was exactly the same tank, but i tried a speaker to the transformer secondary and no sound. So that isolates it to the input stage but i still don't find anything wrong there. So that seems to leave the tranny. How can i check that?

[52 Bill]

So that isolates it to the input stage but i still don't find anything wrong there. So that seems to leave the tranny. How can i check that?

Resistance tests of the primary and secondary windings, shorted turns test with R.G.'s neon lamp tester and replacement.

[Enzo]

Leaves the tranny??? Leaves the whole drive circuit. The tranny is just the last thing in the line.

Is there drive at the transformer primary? Is there B+ at the drive tube plate? Signal there? At the grid? Is there cathode voltage to indicate tube current? etc etc etc.

[daz]

Leaves the tranny??? Leaves the whole drive circuit. The tranny is just the last thing in the line.

Is there drive at the transformer primary? Is there B+ at the drive tube plate? Signal there? At the grid? Is there cathode voltage to indicate tube current? etc etc etc.

Well, i'm just saying there IS reverb, it's just very weak so there is apparently signal and I cannot find any components that are bad. I can't get under the board to look for bad joints w/o painful removal so that will be a last resort. And yeas, as i said above theres normal voltage at the plates. So testing the tranny seems like the easiest thing to do at this stage that is a possibility. Anyways, can't get back to it for a few days.

[Enzo]

Of course it could be the transformer, they do fail, just not often.

Since the rest of the amp works (yes?) we have good signal at the FX return. I might prefer a signal tracer, but a scope works too. check the signal at the FX return jack as a benchmark. Still there at R33? I hope so because your dry signal is also branching through R31. Once it goes through C17 to R34, I expect it to lose some bottom end and reduce in level by maybe a third. Then R32 takes us on into the grids. Got good signal at the grids? We want to trace the signal part by part through that circuit.

When you said you didn't find any bad parts, did you pull C17 and measure it? You don't need to pull the board to get on these parts with a scope/tracer probe.

How is the tube function? Are both sides lit? I'd expect something in the 5ma region for current, give or take a couple. so is there something like 4-5v on the cathodes? Are we getting about a volt or two of signal at the grids? If so, are we getting 30-40-50-60v of signal on the plates?


If you suspect the transformer still, then about any reverb transformer can be subbed in there to find out. In fact if I had something like a Champ OT in the shelf I might use that for the test. Come to think of it, the thing only needs to be powered a few seconds to determine if the transformer made the diference, so really then ANY OT would work. I might clip in half of some OT like for a Deluxe and see if it works. It won;t hurt such a transformer to be so used for a moment.reverb.

[g1]

Yes ^^^^^. We know you have a scope, as much as you may hate to use it .

[Enzo]

Frankly, maybe a signal tracer is more intuitive for you. Easy enough to make a tracer, then you can listen to what is at each stage.

[daz]

Frankly, maybe a signal tracer is more intuitive for you. Easy enough to make a tracer, then you can listen to what is at each stage.

I have one i made years ago. But i won't be able to work on it for a few days. When i do i'll try all these ideas. Thanks.

[daz]

Ok, i used a signal tracer and there is plenty of signal going into the tranny, but nothing whatsoever on the other end at the grid. And yes, the pan is connected. So i assume this must be the tranny, no?

[Enzo]

OK, so sub the tranny, I suggested a couple ways to do that that might use things you already have.

And since it seems like it has to come out anyway, go over to RG's Geofex page, look up the transformer tester, and make one. Test the tranny.

[daz]

OK, so sub the tranny, I suggested a couple ways to do that that might use things you already have.

And since it seems like it has to come out anyway, go over to RG's Geofex page, look up the transformer tester, and make one. Test the tranny.

I'll just sub one in from another amp. Looks like it must be the tranny tho. Does the same thing with different cables and 2 other pans, one a exact same model. So with strong signal at the driver tubes plate and nothing on the other side of the tranny i can't see any other possibilities.