1967 Ampeg Reverberocket 2 Reverb Not Working

[g1]

So, you'll need to verify Pin 7 voltage reading. If it is high like stated, there's something in the circuit area that doesn't belong.

Grids can sometimes not like being measured to ground. Measure with your black probe on the cathode, red to grid. Then subtract that number from what you measured from cathode to ground.

[Steelwitch]

Grids can sometimes not like being measured to ground. Measure with your black probe on the cathode, red to grid. Then subtract that number from what you measured from cathode to ground.

I measured voltage from grid to cathode (P7 to P6) and it was reading -173vDC.. I might check with another meter just to verify. I'm not sure if it's within range of what nevetslab stated should be correct. My head is really starting to spin with this one.

[Helmholtz]

I measured voltage from grid to cathode (P7 to P6) and it was reading -173vDC.. I might check with another meter just to verify. I'm not sure if it's within range of what nevetslab stated should be correct. My head is really starting to spin with this one.

With 1.6V at the cathode (P6) and 147V at the anode (P5) the tube works fine and you can be pretty sure that the grid is at 0V. Actually no need to measure grid voltage. It seems that you meter leads excite some oscillation which causes wrong readings when connected to the grid.

[nevetslab]

Any luck with getting signal on the scope thru the Reverb Drive stage and from the Reverb Return gain stage?

[Steelwitch]

Any luck with getting signal on the scope thru the Reverb Drive stage and from the Reverb Return gain stage?

I had to take it off the bench for a few days to get some other, more time sensitive repairs done but I’ll be updating the thread later today!

[Steelwitch]

As for where to connect your scope probe to look at the signal going to and coming from the reverb tank (once you get the circuit voltages corrected for Section B, you can look at input to grid of 6U10 pin 11, junction of a 2.2M, 220k & 0.1uF plate coupling stage preceding this stage, then look at the connection following the 0.47uF cap off the plate of 6U10 pin 2 (6U10-A). This would be the reverb drive signal. The Return signal can be found at the wiper of the Reverb pot (when the pot is at max CW), this being from the plate of 6U10 pin 5 via 0.005uF. The Reverb signal mixes with the dry signal at the grid of V3 12AX7-pin 7.

A quick check on the Reverb tank for DC resistance on the tank input and tank output will usually confirm the tank being ok, and not indicating an open tank xfmr coil.

Ok, so input to grid of 6U10 on pin 11 is good, coupling stage off pin 11 looks good, however there is no signal across the .47 cap off of pin 2, and the signal I'm getting directly off of pin 2 looks very unstable and unclear. the return signal is perfect.

I have switched from the internal reverb tank to a known working one. the stock reverb tank has about 200ohms on the input and nothing from tip to sleeve on the output, although I don't totally trust that it's an open transformer.. I'm starting to have buyers remorse for this Klein mm500, its not always accurate. I really need to grab myself a fluke.. anyway, it seems like this wima .47uf cap is suspect? thoughts? I gave it a quick look in circuit and it tests perfectly, but I should disconnect a leg just to double check.

[Steelwitch]

weirdly enough, I just got an ampeg reverberocket r-12rt in that has the same reverb issue. 6u10 as well, I'd love to know if this is a similar problem between them

[g1]

Any tank should read less than 1K DC resistance at the tank output jack. If it reads open it is bad, or a wire to the jack is broken.
You said in the first post you knew ("for a fact" ) the tank was ok, so we did not second guess you. How did you determine that? Did something change?

edit: sounds like you may just be having a meter problem, if so, ignore this post.

[nevetslab]

Ok, so input to grid of 6U10 on pin 11 is good, coupling stage off pin 11 looks good, however there is no signal across the .47 cap off of pin 2, and the signal I'm getting directly off of pin 2 looks very unstable and unclear. the return signal is perfect.

I have switched from the internal reverb tank to a known working one. the stock reverb tank has about 200ohms on the input and nothing from tip to sleeve on the output, although I don't totally trust that it's an open transformer.. I'm starting to have buyers remorse for this Klein mm500, its not always accurate. I really need to grab myself a fluke.. anyway, it seems like this wima .47uf cap is suspect? thoughts? I gave it a quick look in circuit and it tests perfectly, but I should disconnect a leg just to double check.

So, input to 6U10 Pin 11 looks good & stable, output at Pin 2 is not, and no signal on the tank side of the 0.47uF cap. What happens if you unplug the input to the reverb tank? You switched tanks to use a known working tank. Are they similar in input/output impedance? In this case, are the DCR reads similar. For example, an Accutronics 4AB3C1B that we find in Fender Twin Reverbs, DCR input is less than 10 ohms (driven by small transformer by 12AU7 tube, both stages), output DCR around 250 ohms.

The Return Signal is perfect. Meaning you can inject oscillator signal into the return circuit and all is well, or you get the reverb tank signal thru it just fine (off 6U10 Pin 5, or further down stream off the 12AX7 Pin 6, which is mixing dry with wet signal (from the tank circuit).

I haven't had one of these amps on my bench in years. Just have the Jet's, Super Jets, Super Rockets in our inventory.

[g1]

Is this one of those amps with a hardwired footswitch? If there is a stuck switch or cable fault, it would ground the signal on the tank side of that .47 cap.

[Steelwitch]

Okay y’all, I’ve learned a valuable lesson today— I reflowed the solder on the tip and ground connections on the Reverb tank and now the reverb works! There is another present issue where the reverb trails off into feedback if it’s turned up past noon. There’s also a considerable amount of noise coming from the tank. I cleaned the RCA jacks with deoxit and the connection is good. I know these tanks tend to fail over time, but I would like to figure out if it’s the tank or something else. Anyone familiar with this happening?

[doctorock]

Okay y’all, I’ve learned a valuable lesson today— I reflowed the solder on the tip and ground connections on the Reverb tank and now the reverb works! There is another present issue where the reverb trails off into feedback if it’s turned up past noon. There’s also a considerable amount of noise coming from the tank. I cleaned the RCA jacks with deoxit and the connection is good. I know these tanks tend to fail over time, but I would like to figure out if it’s the tank or something else. Anyone familiar with this happening?

Same issue here on a '64 GS12R. Been trying everything, no dice. 90% of the info online deals with acoustic coupling, where the tank is being vibrated by the cab or speaker and feeding back. On mine it is NOT vibrational, rather something in the circuit...

[doctorock]

Steelwitch did you ever solve this one?

[SoulFetish]

Doc, you stated that you issue is not caused by acoustic feedback/vibration. Can you post some of the troubleshooting steps you've already taken to eliminate this as the problem, and whatever else you have done?
This will help us help you by not covering ground you've already covered. Thanks.

[Steelwitch]

Steelwitch did you ever solve this one?

I did! I ultimately ended up replacing the tank altogether because it was prohibitively noisy, but the problem was resolved by tightening the mounting on the tank itself, the loose tank was being vibrated by the magnetic field of the speakers voice coil