Rheem California 1909R trem problem

[drewl]

Well, got this old solid state amp up and running, tacked in parts to see if it works.

Need to replace filter and coupling caps,
But I'm having trouble figuring out the tremolo circuit.

Mainly what I think is the selenium rectifier
Tried subbing in diodes, is it a bridge?
It only has two leads.

Here is the trem circuit

[drewl]

Just to add, the circuit powers a bulb in front of a photocell.

Bulb works, continuity through the leads, but there is no voltage across the leads, ac or DC.

Replaced the caps and diode in the circuit.
Speed pot good, must be something with the 20PH6RG device.

[Helmholtz]

How can I rotate the pic without rotating my computer?

[drewl]

Maybe if I rotate the amp the electrons will flow down hill and the circuit will work!

[g1]

How can I rotate the pic without rotating my computer?

You have to save it.

[Helmholtz]

Bulb works, continuity through the leads, but there is no voltage across the leads, ac or DC.

If the lamp produces light there must be voltage across its leads.

Continuity without voltages means a short.

[Helmholtz]

Can see an LFO except if there's something like a DIAC.

[drewl]

If the lamp produces light there must be voltage across its leads.

Continuity without voltages means a short.

Lamp does not light in circuit, I pulled it out and tested it.
It lit at about 12v ac.

Diac, haven't read about those in a while.

Is it possible the mystery device is a dual diode?

There are only two leads, no continuity to chassis/case and diode tests 2.5v in one direction.

[g1]

The only data I have for it says it is a diode and that the + or red marking indicates cathode end.

[drewl]

Same here, thanks.

Well, I need to make some kind of oscillator circuit
The photocell works, resistance varies nicely with varied light.

[drewl]

Well I've tried several different types of diodes in place of the 20ph device with no luck.

Any idea what type of oscillator circuit this is supposed to be?

Thanks.

[Helmholtz]

Any idea what type of oscillator circuit this is supposed to be?

As there are no active, amplifying components it would have to be a relaxation oscillator.
It requires a triggering component like a Shockley diode, a Diac or a neon bulb.

[The Dude]

If you're replacing a selenium rectifier, you may need to add a series resistor. Can you upload a picture of the device? That may help us identify it. Also, many selenium rectifiers have the cathode side marked with a plus sign (IMO- bass ackwards), so make sure you install the replacement properly oriented.

[drewl]

If you Google the part number, pix of it come up, described as a selenium diode and yes, the cathode is marked with a +.

I tried using Schottky diodes in place of it with no luck.
Unless the bulb is supposed to be neon, there are no other devices in the circuit

Thanks, I'll read up on relaxation oscillator circuits and see if I can find something similar

[Helmholtz]

No reason for a Schottky diode here, Don't mix up Schottky and Shockley diodes.
The triggering element needs to have a fold-back or negative resistance characteristic.
What type is the other diode?