Silvertone 1484 Tremolo Help

[misterc57]

I have no tremolo and not sure why. Schematic attached. It seems like I have no audio signal at the tremolo circuit. I do not have a foot switch and am not sure if one is needed. Reverb is working.

I have audio signal coming out of both plates of V3. Each signal leaving the plates go through a resistor, R33 and R34. There is no audio signal on the other side of each resistor.

I believe that is the signal path to the tremolo circuit.

Thank you for your help!

Sears_Silvertone_1484_Twin_Twelve_REPRODUCTION_Manual.pd f

[Enzo]

The footswitch is a trem killer in this model, contrast Fender where the footswitch enables the trem. So trem works without pedal.

V3 has nothing to do with the trem, it is your phase inverter. The two resistors connect to B+ so there would be no signal there.

The trem photocell connects back to C9 and R9 between V1 and V2. Trem only affects Channel 2.

Max the trem intensity control. DO you have a LARGE moving voltage at pins 1 and 6?

[misterc57]

Hi Enzo

With either Strength, Speed or both raised, there is no moving voltage at pins 1 and 6 of V1. Steady 96 VDC at both pins.

Did you want me to check V2 as well?

If I put my signal listener at pin 6 of V6, I do hear pulsing ground noise (with no audio) that fluctuates with the 2 tremolo controls. I also notice that if I max out the Speed pot the pulse stops, if I back off the pot it does not kick back in unless I tap on the pot. Probably needs more cleaning.

Thank you, MarkO

[Enzo]

I am sorry, I was not clear. V6 is the trem tube, not V1. Pins 1 and 6 of V6. leave the speed at half way since it seems to stop at max. You apparently have a trem signal at pin 6, the oscillator, but wwith depth at max, do you get it iat pin1? Pin 1 drives the bulb in the opto.

[misterc57]

Here we go.

V6 pin 1, no pulsing DC, steady at 72 VDC, far lower than schematic indicates it should be 120 VDC, Is low DC an issue here?

V6 pin 6; pulsing VDC between 166 and 173 with speed pot at 75%.

With signal listener I hear the pulse at pin 6, none at pin 1.

Testing done running chassis on a isolation variac at around 115 VAC setting.

Update: I found the tremolo roach. The bulb side is open across the two wires. Not sure if that is right. The oscillator side has 530 ohms across its leads. Also, schematic implies V6 pin 1 plate voltage is fed through the bulb?

[misterc57]

Pics of the roach. The orange wires are the bulb side. Bulb is between V6 pin 1 and filter cap C25C. I have 159 VDC at C25C and 72 VDC at V6 pin 1. Is low DC at pin 1 due to no pulsing?

[Helmholtz]

Bulb is between V6 pin 1 and filter cap C25C. I have 159 VDC at C25C and 72 VDC at V6 pin 1. Is low DC at pin 1 due to no pulsing?

Supply voltage at C25C looks low. Should be around 200V. Check screen supply node voltage (340V) as well as R58, R59. Also some section of C25 might be leaky.

Check for pulsing voltage across R56.

[Enzo]

The bulb is neon, it will have no continuity.

You have pulsing at V6-6, that is the trem oscillator. SO it works. You have no pulsing at pin 1, which drives the bulb. SO is there pulsing at pin 2? At the top of the intensity control? At R54? At C54?

Is there ANY DC voltage on pin 2? It sounds to me like your pin 1 triode is just stuck ON. And the intensity pot? How does it check?

[Helmholtz]

It is obvious that the neon is on/conducting, otherwise plate (pin1) voltage would be zero. But as a neon stabilizes its voltage, I don't expect much pulsing at the plate. Neon brightness is modulated by its current (not voltage) which should show by a pulsating voltage across R56 (cathode, pin3).

[misterc57]

I probably missed something I was asked to check. Here are my observations and readings.

Is C25 leaking? I checked each leg for resistance to ground. All 3 were 93M ohms. Is there another way to check?

C25 readings include R58 and R59

R58 = 85K , too high?
R59 = 69K

C25A VDC = 308
C25B VDC = 200
C25C VDC = 159

6L6 pin 3 VDC = 308
6L6 pin 4 VDC = 420

V6 pin 1 VDC = 75 to 76, pulsing
V6 pin 2 VDC = very low mV, readings that are pulsing
V6 pin 3 VDC = 1, pulsing

This differs from prior checks where V6 pin 1 was steady. Not sure what changed this but I did heavily spray the SPEED pot.

Now that I see some pulsing I hooked up a speaker. I can hear the pulsing in the background, affected by the TREM pots, but the guitar signal is not mixed with the TREM effect. I am getting a dry guitar signal with trem pulsing in the background. There is no foot switch installed.

Thank you all for the help. Never had to work on a tremolo circuit before.

MarkO

[Helmholtz]

R58 = 85K , too high?
R59 = 69K

C25A VDC = 308
C25B VDC = 200
C25C VDC = 159

6L6 pin 3 VDC = 308
6L6 pin 4 VDC = 420

Did you mix up 6L6 pins 3 and 4? Pin 4 voltage must be identical to C25A voltage.
All supply voltages are low by more than 10% compared to schematic. What is your heater voltage (measured across pilot lamp)?

R58 = 85K , too high?

Yes.

[misterc57]

More updates.

I plugged into the wall outlet and my voltages increased about 10%. Yes I did swap the readings on pin 3 and 4 of the 6L6.

A few readings plugged into wall outlet.

Heaters at lamp; 6.26 VAC.
6L6 pin 3 VDC = 452
6L6 pin 4 VDC = 333

I swapped V6 with another tube. No change in behavior.

I still have the background pulsing (it is a squeaking sound) coming through the speaker with the dry guitar signal. Pulsing can be altered by the trem knobs and it can be turned on/off when I use a foot switch.

Why is the guitar signal not mixed into the Trem effect? I am trying to follow the signal path, not sure I understand where it enters and leaves the tremolo.

I have an audio signal at R9. I do NOT have an audio signal on any of the lugs of the two trem pots. No audio signal at V6 pin 2.

My R9 is in the 330K range. I have found two 1484 schematics. One shows R9 = 220K, the other 330K.

Thank you

[Helmholtz]

V6 is not in the signal path.
Use your Ohmmeter to see if the resistance of the LDR (light dependent resistor connected between ground and R9) in the roach is pulsing (use low trem speed as meter my be slow).

And replace R58.

[misterc57]

V6 is not in the signal path.
Use your Ohmmeter to see if the resistance of the LDR (light dependent resistor connected between ground and R9) in the roach is pulsing (use low trem speed as meter my be slow).

And replace R58.

Resistance is pulsing from 830K to 900K, this was about the max I could dial in.

R58; I have to order 68K resistors. I have thousands of resistors but not the one I need.

[Helmholtz]

Resistance is pulsing from 830K to 900K, this was about the max I could dial in.

That's very little variation, probably too small for a noticeable tremolo effect. Tremolo works by variable voltage divider consisting of R9 and LDR. Let's see how things improve with new R58 and increased C25C voltage.

I plugged into the wall outlet and my voltages increased about 10%.

Where was the amp plugged in before?