Odd field coil circuit

[drewl]

Refurbing an old Gibson GA-75W,
Amp works, needs the usual etc. But aside from the usual field coil output trans set up, it has
A 125 ohm resistor in parallel with a 40uf cap in parallel with a coil and selenium rectifier that are in series.
This circuit is fed the input ac line voltage.

Anyone have any idea why or can point me to any other examples of a similar circuit?

All of this is attached to the speaker and doesn't appear on any schems I've seen.

[drewl]

Okay, so after writing that out, the circuit rectifies the line voltage to feed the 1k coil to energize the speaker?
The cap there for filtering.

So, selenium rectifiers, do they diode test like regular diodes?
This one doesn't in diode test mode, but it does measure around 2 meg ohms one way and infinity the other.

[Tom Phillips]

...So, selenium rectifiers, do they diode test like regular diodes?...

The principle is the same but selenium rectifier assemblies have different characteristics than silicon diodes. The forward voltage drop of each individual cell within the selenium rectifier is ~1V. I think you would assume that there is at least one cell per cooling fin. The total forward voltage drop of the series cell stack is probably too much for your meter's diode test mode to deal with. Same problem with the low voltage your meter uses in the resistance measurement mode. I.e. the test voltage is too low to forward bias the selenium diode stack and thus turn it on.

[drewl]

It seems so.
After replacing that circuits filter cap, the voltage came up nicely, so the selenium is good.