Help with intermittent reverb diagnosis: '65 drri?

[52 Bill]

From your test it would appear that the front jack is the return jack and the back jack is the send.

Plug the output from the original tank into the front jack. Rattle the tank and see if there is the traditional spring rattle sound coming from the speakers. The loudness of the sound should be dependent upon the reverb control setting. If this works, then the return circuit is ok.

As for the other tanks, wait until you have an answer to the problem before you swap them out. You will eventually be able to try the different tanks to see how the fullness and delay of each one compares with the others.

[Mango Moon]

From your test it would appear that the front jack is the return jack and the back jack is the send.

Bill,

I apologize for my confusion here, but I'm afraid the terms "front" and "rear" jack don't compute. Could you please be more specific? In other words, when you say "front" and "rear" jacks, do you mean "front" as in closest to the grillcloth (i.e., the one closest to the front of the amp = the one that buzzes when touched)? Or by "front", do you mean closest to me when viewing the amp from the open rear panel (i.e., the one that is dead quiet regardless of reverb pot setting)?

Again, I apologize for the confusion, but I want to make sure that I'm perfectly clear here.

Thanx for help and your patience.

[JoeM]

On my DRRI, the jacks are color coded. White = Reverb send (Pan in), located closer to the rear of the amp, and Red is the Return (Pan out) - located closer to the grille.

[Mango Moon]

Thanks for clarifying Bill - I'll get after it straight away, and no, unfortunately, the two RCA jacks on my DRRI are not color coded. I sure wish they had been. It would have made things far easier.

[Mango Moon]

O.K., I've gone ahead and color-coded my FRONT/RED RCA jack per discussion using a red felt marker (i.e., front=grill=red=pan out & rear=back panel=white=pan in), and with the connections made as specified earlier, the reverb pan does indeed 'crash' audibly when tapped or jarred, regardless of volume setting, and seemingly, irrespective of reverb pot setting. In other words, the 'crash' sound, sounds essentially the same in both volume and magnitude when jarred regardless of volume (1-10) or reverb setting (1-10).

So, if the Return circuit is acting properly, what's next?

Thanx Bill

[52 Bill]

Well the return circuit is working, but you should be able to turn down the crashing sound by turning down the reverb control. The volume control will have no effect on the return signal. There may be a problem with the reverb pot or a bad ground connection in the circuit. Unplug the amp and visually check the reverb pot and the circuit board connections. Check the resistance of the pot with your meter.

Next test is to check the drive signal coming from the amp going to the tank. If you have a small 8 ohm speaker you can hook it up to the send jack (white)and listen to hear a signal coming from the amp. The volume control will need to be turned up to hear this. The sound will not be very good, but if you do hear a signal, then the drive circuit is probably ok.

[Mango Moon]

To summarize then,

The reverb on this amplifier fails to work (with foot switch fully disconnected), despite a perfectly functional reverb pan and perfectly good set of reverb/RCA cables, and despite confirmation that the Reverb Return side of the circuit is working properly (i.e., it crashes when bumped or jarred). When re-connecting the foot switch and repeatedly switching the Reverb On/Off, it remains without reverb, regardless of reverb pot or volume settings, and regardless of foot switch position. This would seem to indicate (from what I've learned so far) that its the Reverb 'Send' side of things that is malfunctioning, but two successive replacements of 12AT7 reverb driver (V3 = Reverb Send) have taken place, along with replacement of V4 (Reverb Return), without a change in performance either way . . . what else is left? Anybody?

[Mango Moon]

Bill,

It looks like our most recent postings passed each other by a minute or so. Anyway, I'll be glad to conduct these various tests that you've suggested, but it will take me some time, probably Monday or later. I'll have to try and dig-out another 8-ohm speaker from the garage, and I'm not particular clear on how I would make such a speaker-to-RCA connection (i.e., speakers have two terminals +/- and an RCA jack is a lone jack). Do I simply connect the RCA to the SEND jack and touch the other end of the RCA wire to the + terminal on the speaker? I'm afraid I'm lost on that one.

As for diagnosing the resistance on the reverb pot itself with a multimeter, I believe I know how to properly jumper the two bridges on the pot, but what should I be looking for in terms of values there (both units of measure and magnitude)? Are we talking <200 ohms again?

Now, you see what you've gotten yourself into here? That'll teach you to respond to such novice inquiries! Haaaa!

Seriously, many thanx Bill!

P.S. - I wonder if I should try and throw a 12AX7 in the V3 (Send) slot just for grins?

[Prairie Dawg]

The only thing left is the transformer. Easy enough to test.

[Mango Moon]

If that's the only thing left and its easy to test, could you please provide me with some guidance on how to do so? I would be forever grateful. That's the whole point of this journey!

[Prairie Dawg]

It should be easy enough to locate where the primary and secondary windings terminate, lift one side of each and check them for continuity. If one or the other side shows very high or infinite resistance it's open.

[Mango Moon]

Thanks Prairie Dawg!

My sincere thanks also to Bill52, BigKahuna and JoeM for their contributions to this effort, but I'm afraid this ones probably gotten to the point where its over my head. Hell, I don't even know how to identify the reverb transformer from the OT, PT or other components present in this amplifier, much less distinguish between primary and secondary windings!

The truth is, when I first set-out to resolve this issue, I had hoped the problem would turn-out to be something that I (the owner) was capable of diagnosing and fixing (e.g., a bad tube or wire or maybe a bad solder point somewhere), but it now sounds like the problem is going to be much-much deeper than that (i.e., that it may require one or more replacement parts and hardware replacement efforts that I'm not qualified to conduct). Very frustrating.

Is this the general conclusion that everyone has come to on this? In other words, has the reverb transformer been firmly identified as the only remaining possibility here? And if so, how common (how expensive) is this sort of a repair?

Thanx All!

[Prairie Dawg]

Lift one side of the primary and one side of the secondary. Check them for continuity . The reverb transformer is the little dinky one that's mounted on an angle.

[Mango Moon]

Lift one side of the primary and one side of the secondary.

Huh?????

Sorry Prairie Dawg, but no-comprende the terms "lift" or "primary" vs. "secondary". As I've repeatedly said earlier in this thread, I'm not a trained amp tech. I have positively identified the reverb transformer (based on what you've said here), but I'm afraid that's the extent of my knowledge on it. So if you'd like to be more specific about what the term "lift" means or how to do it, and also how to distinguish primary from secondary, that'd be great. I'll be happy to conduct whatever testing you suggest.

Thanx

[Prairie Dawg]

There are two pairs of wires coming out of the reverb transformer. these connect to the primary and secondary windings of the transformer. Disconnect one of each and then test each side for continuity. If the resistance is low or nil, the transformer is probably OK. That's about as simple as I can make it. If that's beyond your knowledge base better call for reinforcements.