Deluxe Reverb Oscillation Problem - Reverb Driver stage?

[waspclothes]

Hey guys,
My Deluxe Reverb is making some weird noises! I've never actually heard an oscillation before, but this is definitely an oscillation noise that kicks in once the volume gets high enough (either on the volume knob, or by really hammering the strings) and goes away when the input volume dies down again. It sounds like a buzz/fuzz note, louder and on top of the guitar itself. When trying to isolate the problem, I found that either disconnecting the reverb tank INPUT or removing the reverb tank driver tube the oscillation went away mostly.

I tried some different tubes, any 12AT7 caused the same problem. I had a 12AU7 lying around, and this did not cause any problems. I'm guessing because it is a way lower gain tube.

I tried moving the lead dress around with a chopstick and that didn't seem to do anything.

I tried changing reverb tanks and that seemed to work, going from an "A" 8 ohm input, the only other tank I had to try was a "B" 150 ohm input. This stopped the oscillation/noise/distortion. Interestingly, when I switched to the B tank, I heard a "popping" at high volume (10) and found it to be arcing between pins 5 and 6 (or 6 and 7 I forget).

When the oscillation was happening, I could see spikes with the oscilloscope on the speaker output, reverb driver input and even as far back as the volume knob and the grid of V1! But as soon as I pull the reverb driver tube, it doesn't happen. I'm at a loss, any ideas?

[g1]

Where was the arcing, at the reverb driver tube? I think it may be the same issue with both tanks, just one is more pronounced. Clean up and resolder the socket and see if you can stop the arcing, then try the other tank again. Also make sure you have good ground connections at all the RCA connectors.

[waspclothes]

Where was the arcing, at the reverb driver tube? I think it may be the same issue with both tanks, just one is more pronounced. Clean up and resolder the socket and see if you can stop the arcing, then try the other tank again. Also make sure you have good ground connections at all the RCA connectors.

Yeah the arcing was at the reverb driver tube. I only saw it with the B reverb tank, but I wasn't looking in the dark. Thanks for the advice, I'll try what you said and post back the results.

[52 Bill]

Yeah the arcing was at the reverb driver tube. I only saw it with the B reverb tank, but I wasn't looking in the dark.

The arcing was probably caused by the mismatched impedance load on the reverb drive circuit.

Which model of Deluxe Reverb is this?

[soundguruman]

Depends on which Deluxe it is.
The newer ones have a problem with bunk plate resistors.

I have seen some bad reverb RCA jacks, the ones that are mounted on the plastic plates.
The ground fails, because the metal is crimped together...and when that fails, it causes all kind of problems.

Conceivably, because of that, it may cause the reverb driver tube to arc.

You "can" solder the crimped metal together, and that usually fixes it.

[g1]

The arcing was probably caused by the mismatched impedance load on the reverb drive circuit.

Agreed, I misread those impedances and was barking up the wrong tree. You shouldn't test with a "B" input impedance tank.

[waspclothes]

Looks like I found what the problem is today. As soon as I moved the wire between pin 1 and 6 on the reverb driver tube, the buzzy distortion went away. The wire was right up against the tube-base screw, and moving it away from that screw stopped the problem.

What was happening? Was it some sort of capacitance thing, or arcing between the wire and screw (even with the insulation)? Something else?

Thanks for all the help guys, I'm happy this problem is gone. Now to figure out why the Vibrato channel sounds brighter and less-ballsy than the normal channel, even though the bright cap is clipped!

[Leo_Gnardo]

I'm happy this problem is gone. Now to figure out why the Vibrato channel sounds brighter and less-ballsy than the normal channel, even though the bright cap is clipped!

As you said, either arcing or some ultrasonic oscillation thing. "Bright cap" I assume you mean the 47 pF on the volume pot. You have a lot of opportunity to "voice" the Vib channel, look at the spot where dry & reverb are mixed. The dry signal arrives thru a 3M3 resistor paralleled with 10 pF. Reverb thru a 470K resistor. Ground path via 220K resistor - for simply a tad more volume you could bump that up to say 270K to 470K. Or else to strengthen the dry signal leave that grounding R alone, reduce the 3M3 to 2M2 down to say 1M, and if still too bright reduce or remove the 10 pF cap.

[jpdesroc]

Same oscillating DRRI issue resolved..

Same DRRI issue resolved..
I had this bad oscillations (around 5khz buzz) passed around 5 on the volume
controls (channel 1 or 2). No oscillations below 5 on vols.
These oscillations got worst when the reverb pot was raised.
Was oscillating with V3 removed or not. It stopped completely
whenever I had V4 removed (using channel 1). Then I saw elsewhere on the web that
a tech worked on a same DRRI oscillation issue and found the problem to be
bad(s) supply filter capacitors.
So I had a look at all the caps under the top filter caps metal hood.
Guess what !
C33 22uf/500v was completely open (Z test point)
C32 47uf/500v was leaking at its positive end.
So paralleled C33 with a good 22uf cap and VOILĄ !
All the oscillations were gone.
One note: even when oscillating at the speaker output
C33 positive lead (Z test point) was not showing any signs
of oscillation when check on the scope (DC only with little ripple)!!
--> Don't mess too long with xxxxpf cap values
placed on some offending (oscillating nodes) circuit parts..
The original circuit should work with stock parts !
I replaced ALL the electrolytic caps under the hood
and the amp is doing fine now.
Hope this will help you.
BTW the offending caps where Illinois Capacitor branded.
This is not the first time I stumble on bad IC capacitors..
It was on a Peavey Joe Satriani combo.
J-Pierre

[TimmyP1955]

We've had several TRRI with an issue right out of the box: OK at nominal levels, dimed it had a very nasty breakup (owing to oscillation perhaps?). Unplugging the tank or removing V3 solved the issue, changing V3 did nothing. As they were new, I did not dive in, we just sent them back. If we get another with the issue, perhaps I'll have a peek inside.