DeArmond (Rowe) Guitar Amplifier Model R25T Restoration

[misterc57]

Have you checked that V1 pin8 voltage is good, and it's cathode cap?

I have replaced the two .01 disc caps with new poly.

V1 pin 8 has a new cathode cap. I'm reading from 1.6 to 3.2 V based on position of the depth pot.

edit. all caps and resistors are within specs. The only one far off is the .022 cap reads .03.

[g1]

V1 pin 8 has a new cathode cap. I'm reading from 1.6 to 3.2 V based on position of the depth pot.

Is this DC voltage steady or pulsing? It should be a couple of Hertz pulse. I think you will need to scope around the V5 to see whether the oscillator is running properly.
Pin 1 of V5 would be the most noticeable place to see the oscillation.

[misterc57]

Rate and speed pots at half way. No pulsing on any V5 pin. Also tried with the varistor back in circuit.

V5 pin 1 150 V
V5 pin 3 1.6 V

V5 pin 6 332 V
V5 pin 7 150 V
V5 pin 8 152 V

V1 PIN 8 steady No pulse

[g1]

Are you using the footswitch or have you verified the grounding contact at the footswitch jack? Maybe try manually grounding the circuit where the jack connects.
It seems to me you had some oscillation from the LFO earlier in the thread, but now you have none. Or maybe the earlier time was also just when you were moving the pot?

[misterc57]

Are you using the footswitch or have you verified the grounding contact at the footswitch jack? Maybe try manually grounding the circuit where the jack connects.
It seems to me you had some oscillation from the LFO earlier in the thread, but now you have none. Or maybe the earlier time was also just when you were moving the pot?

I've been thinking that the footswitch jack should be open to ground (which it is) to have the effect ON and closed to kill the effect. That switch jack has been bent so that it is always open, there is no contact between the tip and and switch blade.

Aside, the footswitch is also in need of repair as it is always in high resistance.

Sometimes I would hear a faint oscillation when moving the pots but it would last less than one second. Also earlier I thought I was hearing a faint oscillation but it may have been strings vibrating and wishful thinking.

With a 1K injected sine wave I see no pulsing on the scope and no V pulsing on the DMM.

[misterc57]

Shouldn't there be 3 Cap-Resistor nodes to ground in the tremolo circuit?

Per schematic I only see two. The .022-Rate pot and the .01-2.2M. The .01-1M is not grounded.

Jumping the footswitch jack to ground which would put that 3rd CR node to ground, makes no difference.

[g1]

Jumping the footswitch jack to ground will short out the .01 disc cap.

[misterc57]

Good news. Replacing the two .01 caps in those CR nodes got the trem working!

I have a new 500K audio pot for the depth. Not feeling the trem until I dial up to 8 thru 10. Sounds great at 10 which reads 5 ohms across the two pot lugs. There is no longer a varistor but a 68K resistor following this pot. I would like to have a better reach on the depth pot instead of positions 8 to 10 only. Maybe put the 22K back in place of the 68K?

Thank you!

[g1]

I have a new 500K audio pot for the depth. Not feeling the trem until I dial up to 8 thru 10. Sounds great at 10 which reads 5 ohms across the two pot lugs. There is no longer a varistor but a 68K resistor following this pot. I would like to have a better reach on the depth pot instead of positions 8 to 10 only. Maybe put the 22K back in place of the 68K?

You can try that. I'm also wondering about the taper of the pot. You could try moving the outside lug connection to the other unused lug. It will work backwards but give you an idea if there is more or less useful sweep. But do this before changing the resistor so that does not become a variable.

[misterc57]

You can try that. I'm also wondering about the taper of the pot. You could try moving the outside lug connection to the other unused lug. It will work backwards but give you an idea if there is more or less useful sweep. But do this before changing the resistor so that does not become a variable.

I've tried both sides of the pot with same results just backwards. Schematic calls for CCW 350K. CCW us audio taper, right? I have a 500K audio taper pot installed as I did not find a 350K available online.

I will try some tests including placing the original 22K + Varistor back in place.

[misterc57]

Tremolo sounds great but every configuration is the same, only getting tremolo with depth knob above 8. Kim, how does your depth pot settings compare?

I have the original resistor and varistor back in place. I cannot make out the color band (I am color blind) on this resistor but it read around 15K out of circuit (schematic states a 22K in this position).

I no longer have the shorting .01 disc cap installed. I have all 3 CR nodes connected to ground and I have moved the foot switch jack connection to one of the .01 CR nodes and it is working properly.

Thank you all.

[khmassey]

Yeah mine is kinda opposite. I can’t turn the depth up past about 5 or it’s too much. Still one of the best sounding tremolos I’ve heard.