Silvertone 1484 Tremolo Help

[g1]

Are you getting your -1.5V at the 2.2meg ?

[Helmholtz]

V6 VDC readings
pin 2 ; pulsing slightly above and below 0

I would expect something like +/- 1V here. Check R53, R54, R55 values and measure resistance between pin 2 and ground with tremolo strength at max.

[misterc57]

Note. All below resistance readings were done in circuit.

Are you getting your -1.5V at the 2.2meg ?

No! - 0.6 on the screen side and - 0.68 on the other side of the 2.2M R49. This looks like an issue!

More readings on this line.

Resistor, Spec, Reading

R49, 2.2M, 2.3M
R60, 100K, 763K. Very high, I will lift a leg for a better reading tomorrow.
R61, 2.2K, 2.2K.

I would expect something like +/- 1V here. Check R53, R54, R55 values and measure resistance between pin 2 and ground with tremolo strength at max.

Pin 2 to ground was odd trying to read resistance. At first it was 88K. Then is started to bounce around as high as 1M. Then it went OL for a while, eventually back to 88K. Strength pot at max.

Resistor, Spec, Reading

R53, 330K, 430K
R54, 560K, 567K
R55, 100K pot, 88K across pot end legs.

[Helmholtz]

Pin 2 to ground was odd trying to read resistance. At first it was 88K. Then is started to bounce around as high as 1M. Then it went OL for a while, eventually back to 88K. Strength pot at max.

Sounds like an R55 wiper contact issue. Pot may require cleaning if rotating a few times doesn't give a steady max reading.

[misterc57]

R60 measures good out of circuit at 102K. Is low voltage of -0.69 at R49 (2.2M) a concern?

I have -32 VDC on one side of R60 and -0.69 on the other side.

[Helmholtz]

The left side triode of V6 is the low frequency oscillator (LFO). As the triode has no cathode bias resistor it needs a negative grid bias voltage. The "-1.5V" in the schematic is the bias. This voltage is derived from the 6L6 bias supply by voltage dividing (R60/R61). With the values from the schematic I get - 36Vx2.2/102 = - 0.78V, so the -1.5V can't be correct. As your bias supply only delivers -32V, the result should be only - 0.69V - exactly what you measured.
While the LFO will work with that small grid bias (-0.7V), the -32V might a problem for the power tubes, will make them run very hot. C30 might be leaky. That's not related to your tremolo problem, but could account for generally low voltages.

If you don't get a voltage variation (pulsing) of maybe +/- 0.5V at V6 pin 2 (max strength), C24 is probably bad.

[misterc57]

If you don't get a voltage variation (pulsing) of maybe +/- 0.5V at V6 pin 2 (max strength), C24 is probably bad.

Just learned my meter has a min/max feature. This is pulsing from -0.26 to +0.26

[misterc57]

I read some folks will clip in a capacitor over a potential bad one for testing. Is this true and if so do I just clip it in parallel to the existing cap? Not even sure I have any .05 600V.

[Helmholtz]

It is pulsing really fast. .24 was the highest I could visually see. -.08 was lowest.

Is that at lowest speed? Your meter is probably too slow to follow and show full amplitude. Voltage variation at grid (pin 2) and cathode (pin 3) should be the same.
Anyway try paralleling another 0.05µ cap across C24 and see if tremolo strength increases.

From what you reported earlier you must have a little tremolo (of course only in channel 2) as the LDR resistance varies. Using your scope you should see a little signal amplitude modulation at the node R9/R15/LDR. And cover/shield your roach against ambient light.

[misterc57]

Yes slowest speed. Just learned my meter has a min/max feature. This is pulsing from -0.26 to +0.26

[misterc57]

Anyway try paralleling another 0.05µ cap across C24 and see if tremolo strength increases.

Progress.

I paralleled a .047. Pin 2 has increased to - 0.5 V to + 0.42 V. Tremolo effect still not working.

Should I make the swap of C24?

you should see a little signal amplitude modulation at the node R9/R15/LDR

Not seeing much here. - 0.75 mV to 1.47 mV

[Helmholtz]

Not seeing much here. - 0.75 mV to 1.47 mV

I don't understand the minus value. As DCV at that node should be zero, I expect symmetrical AC signal pulsing in amplitude. What matters is the difference between minimum peak-to-peak(pp) signal and max pp signal.

[misterc57]

I don't understand the minus value. As DCV at that node should be zero, I expect symmetrical AC signal pulsing in amplitude. What matters is the difference between minimum peak-to-peak(pp) signal and max pp signal.

This was measured on my DMM, min and max values. I can redo with the scope. Or would my DMM min/max set to AC do it here? Bear with me, I am learning. Thank you

[Helmholtz]

I meant to feed a (~100mV) signal to channel 2 input and measure AC at the node described. With scope you should see your signal varying in amplitude. With DMM use AC mode. I prefer scope as its faster reacting.

[misterc57]

I meant to feed a (~100mV) signal to channel 2 input and measure AC at the node described. With scope you should see your signal varying in amplitude. With DMM use AC mode. I prefer scope as its faster reacting.

Now I understand better. Will do and report back. Thank you!