Tremolo Not Working-1972 Super Reverb

[kinggabbo]

I just got a 1972 Super Reverb and the tremolo is not working on it. I have a shorted RCA jumper, but it still doesn't work. I took out the chassis and compared it to an amp layout diagram I got from vintagesound.com or the fender amp guide. Where it differs greatly is that the diagram show just a blue wire running from the vibrato pedal jack. In my it has that blue wire, but it also has what looks like a capacitor running to pin 2 of the tremolo tube. Is this normal? I'm new at amp repair and reading schematics.

If this is normal, then any suggestions to fix the tremolo? Thanks.

[Jazz P Bass]

Fender tremelo

Pin 2 has a 0.01 uf capacitor on it.
What amp circuit do you have?
Look down the optocoupler. You should see it blinking when the RCA plug is shorted. the blink rate should go faster when you advance the speed pot.

[kinggabbo]

OK I looked at it (little black tube with 4 little legs, right?). Fiddled with all intensity and speeds settings. Tried with and without the shorted RCA jack. No light at all from the roach. I would be able to see it if it was working right?

So what's the next step? Check wiring? Replace the octocoupler?

Thanks for all the help.

[Albert Kreuzer]

Where it differs greatly is that the diagram show just a blue wire running from the vibrato pedal jack. In my it has that blue wire, but it also has what looks like a capacitor running to pin 2 of the tremolo tube.

Are you sure it is pin 2 and not pin 3? Some SF designs have the 25/25 cap grounded at the vibrato jack.

And what Jazz said. Does the neon lamp blink?

[kinggabbo]

Oh sorry about that. I checked again and yes it is pin 3.

No light at all coming from the lamp/roach/bug/octomom thing.

[Jazz P Bass]

Fender Vibrato

Your next step is to check all your connections.
Use the schematic.
Does the speed pot go to ground, etc,etc.
Once you know all connections are secure , use the schematic and check all the voltages around the tube.
Write down what you measure on the schematic.
Lift the plate end of the opto & see if you have B+ coming through.
If so, it is probably good.
With your meter on Vac, look at the first grid. It should be oscillating.
If not, you have a bad capacitor in that part of the circuit.
Take your time. Use common sense. You'll find the problem.

[Albert Kreuzer]

If not, you have a bad capacitor in that part of the circuit.

When the old electrolytics go dry, the oscillator often will stop oscillating. In this case, this would be the cap going from pin 3 to the vibrato jack ground.

[kinggabbo]

Your next step is to check all your connections.
Use the schematic.
Does the speed pot go to ground, etc,etc.
Once you know all connections are secure , use the schematic and check all the voltages around the tube.
Write down what you measure on the schematic.
Lift the plate end of the opto & see if you have B+ coming through.
If so, it is probably good.
With your meter on Vac, look at the first grid. It should be oscillating.
If not, you have a bad capacitor in that part of the circuit.
Take your time. Use common sense. You'll find the problem.

Jazz P Bass, sorry, I'm kinda inexperienced with amp repair. I have a couple of questions/comments about your post.

1. I did look at the connections. They all look good. Everything seems to go where it's supposed to and grounded as well.

2. Lifting the plate enter of the opto? Is this the front part of the tremolo bug/roach? The part closest to the front of the chassis? What do you mean by lifting it?

3. And then first grid? What is that? Part of the power supply?

Thanks for your help. I am inexperienced but want to learn everything about this and fix it.

[Jazz P Bass]

Tube amp repair

There are some serious voltages in that amp.
If you honestly do not know what you are doing, please, take it to a tech.

[kinggabbo]

When the old electrolytics go dry, the oscillator often will stop oscillating. In this case, this would be the cap going from pin 3 to the vibrato jack ground.

OK. Replaced the tremolo tube. have a real footswitch. Still not fixed. I am going to order a roach and the capacitor you are talking about. What are the specs for the capacitor that I need to order?

[kinggabbo]

Replaced the tremolo tube. Have a real footswitch. Still not fixed. I am going to order a roach and the capacitor that was talked about. What are the specs for the capacitor that I need to order?

Would this work, from Weber? Electrolytic cap, axial, 25uF, 25VDC

[Jazz P Bass]

Pin 3 cathode bypass cap

25uf/ 50 V

[kinggabbo]

Thanks for all the help guys. Things have changed now. I put new power tubes in (unrelated to this problem, I needed new power tubes) and biased them. I also put a new tube in the V5 position for the tremolo. I hooked up the footswitch and I saw the bulb flashing like mad!!! Seemed to get faster or slower according to the speed control. However still not tremolo sound, no matter what I did with the intensity and speed controls. Could the intensity pot need replacing???

[Jazz P Bass]

Vibrato Intensity pot

The intensisty pot is 50K ohms.
Measure the resistance across the two outside legs.
Should be 50,000 ohms.
One leg has to go to ground.
The other leg has to meet the 220K resistor.(follow the schematic).
It may be the roach is bad.
The light that you see blinking should change the resistance of the other half . On the schematic it shows a resitor in a circle.
Turn the intensity fully on & see if you are getting a Vac oscillation at the wiper (middle leg)

[kinggabbo]

OK tonight, the light is blinking and for the first time I finally here something. There is a faint ticking coming from speakers in time with the light that goes faster or slower with the speed control. But no tremolo sound when the volume is turned up. Also, I tested the V5 and the voltage goes up and down. So I guess it is oscillating correctly?

What's the next step in troubleshooting? ( I guess a good step would be testing the Intensity pot, as stated above, will try to do that tonight)