1968 stupid reverb

[davebolden44]

just started some long overdue diagnostics of my super reverb. as i recall the tremolo isnt working but i am going to call that step 2. for now i am trying to figure out why the reverb isnt functioning properly. it just pops periodically, its a light pop with a small amount of pan crash to go along with it. it also has considerable hum when you turn up the reverb control. i swapped the send and return tubes one at a time, swapped the rca cables out, checked all the voltages on the tubes and they were tolerable per the schematic, checked all the associated grounds in the circuit and checked the pot for a good clean sweep, no coupling caps are leaking dc and load resistors were changed out maybe 2 years ago for whatever reason. i also did a chopstick probing for good measure to no avail. is there something i am missing or something common to this circuit? the hum could be partially due to the tank sitting closer to the circuit on my bench and could be due to shielding perhaps. i dont know, any and all insight is most welcome.

[xtian]

Common for reverb tanks to fail. Measure the D.C. resistance of input and output to the tank. Expected values can be found online.

[RightLurker]

Have you checked the filter caps? I worked on a 1967 Princeton Reverb that had a nasty hum in the reverb circuit. With the reverb control turned down there was no hum. When the reverb control was turned up, the hum started and increased the higher the control was set. I tried everything, and nothing fixed it. Finally I changed the filter cap and all was well.

[davebolden44]

yeah the caps were changed and the tank is good. i found the source of the hum and it can be attributed to my own stupidity. i had it sitting in too close proximity of the chassis while troubleshooting. i moved it away and the hum died substantially. the reverb is lush and sounds good. the popping as near as i can figure is just the old carbon comp resistors. later today i will start on the tremolo circuit. all i have determined on that front is something is wrong with the foot switch and the optical resistor still blinks. however it does not work at all

[Stevem]

If the reverb foot switch is not plugged in, and or its ground connection on the RCA end ( amp end or switch end ) is no good, then the foot switch for the Tremolo can not get its needed ground reference to turn on.

In regards to the reverb driver and recovery tube , rock them around in the socket real good to test those Female receivers out in the sockets.

Popping sounds that you can not turn down with the reverb control are coming from 1) the tube, 2) its circuit components, or 3) the tube socket.

Noises and pops that can be turned off come from the driver end of the circuit.
The first thing I do on these amps along with filters is to change out all the plate load resistors in the amp !

[davebolden44]

i replaced all the load resistors when i did the cap job about 2 years ago. the footswitch will turn off/on the reverb how ever when i put the vibrato switch in the reverb circuit it squeals which leads me to believe that the vibrato side of the footswitch itself needs repaired. however the reverb side plugged into the vibrato will engage the optical resistor but the circuit yields no vibrato effect. as far as the popping it is in circuit or the tube socket as you said. its an old amp so i am not surprised. when i make my way down to the bench later i am going to swap v5 out which aside from checking the switch itself i will call step 2.

[davebolden44]

yeah it was a bad switch, open load in both positions of the vibrato switch itself. i had another footswitch laying here and it works fine. thanks for the help guys.