Randall RG-120 No Tremolo (& More) Help

[misterc57]

Any new suggestions?

If I have a signal at the input of the tank, shouldn't I see one at the output of the tank? Springs are good, connected. Tried two different tanks.

Thank you

[Helmholtz]

If the tank and the recovery amp are good, the tank output signal doesn't reach the recovery circuit. Find the bad connection or cable.

To "see" if you have tank output signal, connect tank output to the input of another amp.

[misterc57]

Tried 3 tanks, no output.

I am wondering if the tanks I am trying are not compatible with the circuit. Is it possible to have no output if using the wrong tank?

The recommended tank for this amp is a Accutronics 4FB2A1A. Input impedance 1475 ohms, output impedance 2250 ohms.

The tanks I have tried have much lower input impedance, below 50 ohms and much lower output impedance.

[Helmholtz]

Transducer impedances should be matched to the circuit.
Wrong impedance may significantly lower available reverb level.

[Enzo]

But just about every reverb pan has a B output. His problem is zero reverb, not weak reverb. The recovery circuit is not working.

[Helmholtz]

The recovery circuit is not working.

See post #30 (and #32).

[g1]

You are confusing tank impedance and resistance. FB type tank should be around 200 ohms DC resistance at both ends. So yes, your tank input impedance is low and may be greatly decreasing the signal level. (if 4FB tank recommendation is correct)
What are the number codes on the tanks you are trying?

When you injected signal at the tank output, it should take very little signal to hear it at the speaker, what level signal were you injecting?

[misterc57]

I injected a 200 mV signal to the tank output pins, which made its way through the amp to the speakers.

The tank that was with the amp is a 4BB2C1D (which may not be the original tank), spec 250Ω in / 2,250Ω out.
I also tried a 4BB3C1D, spec; 150 ohm / 2250 ohm
and a 8DB2C1D, spec 310Ω in / 2,575Ω out

[g1]

200mV seems a big signal for the recovery circuit. I don't think any tank is going to put out that kind of voltage.
Again, if the recovery circuit is working right, you should be able to hear the crash if you give the tank a good shake. Whether the tank is right or not will not matter for this 'crash test'.

[Helmholtz]

Reverb pot fully up?

[misterc57]

Not passing the crash test. Reverb pot cranked and in every other possible position. No sound.

[g1]

Typical reverb output is said to be in the 1 to 5 mV range. So when you injected 200mV you were getting an incorrect result. Try injecting 10mV instead.

[Helmholtz]

Try injecting 10mV instead.

That^^.

And scope the Q19 emitter signal (AC coupling). Then trace the signal up to the source of Q3.

[misterc57]

10 mV injected at tank output. Seeing about 1 mV at Q19

I can hear the signa at the speaker. Channel VOL pot has no effect. Reverb pot makes the signal louder, so does the master volume pot

Where is Q3? I will get the scope on it next.

Thank you

[Helmholtz]

10 mV injected at tank output. Seeing about 1 mV at Q19.

Where is Q3? I will get the scope on it next.

As Q18 is a gain stage and Q19 is a buffer, output at Q19 source must be larger than the input.
Means you have a problem around Q18/Q19.

Q3 is the third transistor (JFet 58) in cannel 1.