Silvertone 1484 Tremolo Help

[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.

There is no pulsing at this node, regardless of how I set the tremolo pots.

[Helmholtz]

Just to make sure: You're scoping the node where the LDR connects, right?

Earlier you reported that the resistance of the LDR pulses. If so, you must see some signal pulsing.

[misterc57]

Just to make sure: You're scoping the node where the LDR connects, right?

Earlier you reported that the resistance of the LDR pulses. If so, you must see some signal pulsing.

I am directly on the LDR roach leg for this measurement. Resistance to ground is ranging from 635K to 672K. The waveform on the scope is steady, no changes as one would expect to see the bouncing of the tremolo effect.

[Helmholtz]

Resistance to ground is ranging from 635K to 672K..

Ok, that's almost no change. I assume you effectively shielded the roach from ambient light maybe using heavy tape to cover any opening.(with amp in cabinet there will be no light except for the neon.)

Now pull both power tubes (this will increase DC voltages) and scope again.

Next test will be increasing V6 pin 2 drive by paralleling a 330k resistor to R54.

Alternatively increase V6b gain by tacking a 47µ cap across R56 (27k).

THese are tests to see if the roach is still useable.

[Jazz P Bass]

The LDR can be tested very simply with a bright lamp.
! meg ohm/ no light.
Near 100 ohms with light.

[misterc57]

Before I try anything else, I just discovered something odd.

What is the purpose of R57 15M? I have an open from V6 pin 1 to pin 3. It is a challenge to find components in here but I physically do not see R57

Thank you

[Helmholtz]

I think R57 helps to start the neon and to maintain a very low simmer current when the tube is driven into cut-off thus avoiding re-strike spikes.
But as your V6 pin 1 voltage never drops to zero, the neon must be always on anyway.

Do you know if the tremolo ever worked?

[misterc57]

I think R57 helps to start the neon and to maintain a very low simmer current when the tube is driven into cut-off thus avoiding re-strike spikes.
But as your V6 pin 1 voltage never drops to zero, the neon must be always on anyway.

Do you know if the tremolo ever worked?

I do not know if it ever worked. I got this amp from a clean out guy who knew nothing about the amp.

I doubt I have 15M resistors. Should I clip in a different value and see if anything changes?

[Helmholtz]

I doubt I have 15M resistors. Should I clip in a different value and see if anything changes?

I wouldn't go lower than 10M (what Fender uses). Too low a value will even lower your tremolo strength.
But as indicated I don't think the missing resistor is your root problem.

[misterc57]

The LDR can be tested very simply with a bright lamp.
! meg ohm/ no light.
Near 100 ohms with light.

The roach seems to be really well protected from light. Even though I cover it to make things darker. Resistance does not change when shining a light on it. Stays around 640K. This was tested with the amp OFF.

[misterc57]

Ok, that's almost no change. I assume you effectively shielded the roach from ambient light maybe using heavy tape to cover any opening.(with amp in cabinet there will be no light except for the neon.)

Now pull both power tubes (this will increase DC voltages) and scope again.

Next test will be increasing V6 pin 2 drive by paralleling a 330k resistor to R54.

Alternatively increase V6b gain by tacking a 47µ cap across R56 (27k).

THese are tests to see if the roach is still useable.

Roach protected from light. I got to the first test (pull both power tubes). I now see slight bouncing on the scope, but not until the intensity pot is at 9 and 10. Below 9 there is a steady sine wave. Speed control does change the scope pulsing from slow to fast in the entire range of the pot.

I did not continue with the next test. Should I?

Thank you

[g1]

Have you had a look to see if that metal wrap around the roach can be uncrimped or unrolled? Then you can easily test the resistive part, and also see how much the bulb intensity is fluctuating.

[misterc57]

Have you had a look to see if that metal wrap around the roach can be uncrimped or unrolled? Then you can easily test the resistive part, and also see how much the bulb intensity is fluctuating.

No, but I may have to.

[Helmholtz]

I did not continue with the next test. Should I?

Yes, please do.

[misterc57]

Yes, please do.

Keep the output tubes out when doing the next step?