I'm just finishing up re-capping of this nice Arvin 664.
http://www.nostalgiaair.org/PagesByModel/597/M0012597.pdf

I've been trying to understand why there seems to be two "local" oscillators.

The text refers to L3-c3 as the osc ... and I do confirm that it does operate at 455khz above the RF signal but so does L2-c2.

So why if almost all others use only one local osc why does the circuit seem to require two?

Care to enlighten me?... or point out my mistake?

Hi Peter

At first it sure seems that way. 2 is an RF coil. It takes the signal from RF 12SK7 to grid #3 of the 12SA7. 3 is the oscillator.

Norm

:I'm just finishing up re-capping of this nice Arvin 664.
:http://www.nostalgiaair.org/PagesByModel/597/M0012597.pdf
:
:I've been trying to understand why there seems to be two "local" oscillators.
:
:The text refers to L3-c3 as the osc ... and I do confirm that it does operate at 455khz above the RF signal but so does L2-c2.
:
:So why if almost all others use only one local osc why does the circuit seem to require two?
:
:Care to enlighten me?... or point out my mistake?

Thanks Norm:
.. I can see it a bit better now. The odd way they draw the schematic with the 1st RF plate 12sk7 pin 8 at the bottom of the tube must have led to my confusion. especially as it feeds the 12sa7 too.. that grid is drawn at the bottom like a cathode normaly is... lol

But when I place my freq probe on that first coil L2 it seems to operate at the same freq as the local osc L3 which really confuses me.

Why doesn't it operate at the selected RF freq... or is it just to hard to see that?