A three wire wax bypass cap?!?!?!

[Kamakiri]

Working on this 1940-ish RCA AA5 set, and I run across this. In all the hundreds of radios I've had my hands in, NEVER seen one before. Worst part about it is that the marks on the cap don't correspond to the wires coming from the cap, so I'll have to find a schematic to see what's what.

Not sure of the model number of the set.

[WISCOJIM]

http://www.radioatticarchives.com/radio.htm?radio=11480

[dieseljeep]

Originally Posted by Kamakiri

Working on this 1940-ish RCA AA5 set, and I run across this. In all the hundreds of radios I've had my hands in, NEVER seen one before. Worst part about it is that the marks on the cap don't correspond to the wires coming from the cap, so I'll have to find a schematic to see what's what.

Not sure of the model number of the set.

It's a 1AX, found in Riders 12. Coupling cap to 50L6 grid and tone comp to B-.
I don't remember seeing one of them in an RCA AA5.

Here's the Riders on Nostalgia Air: http://www.nostalgiaair.org/Resources/803/M0014803.htm

Is that the bottom of the 12SQ7 that it's connected to?

[old_coot88]

The values given in the Riders print are pretty smeared and hard to read, but look to be 300 pf and .005 mf (which sounds about right), connected thusly:
(Looks like a predecessor to the notorious 'couplates' of a later decade.)

[Kamakiri]

That's exactly it, thanks! I don't stock anything below 680 PF, so guess I'll have to place an order

[old_coot88]

You could probably omit the 300pf one altogether, as it serves only to cut treble.

Also, judging by the large value of C17 (across the plate of the 50L6), the designers were trying to emphasize the set's bass response at the expense of treble.

[old_tv_nut]

put two 680 pF in series and you'll get 340 pF, which is close enough

[Kamakiri]

You guys are geniuses!

Gonna finish it up when I get back from the Big Apple

[Kamakiri]

Originally Posted by old_coot88

You could probably omit the 300pf one altogether, as it serves only to cut treble.

Also, judging by the large value of C17 (across the plate of the 50L6), the designers were trying to emphasize the set's bass response at the expense of treble.

I know why that capacitor is there....because it sounds like a tin squawk box without it

Thanks for the help! She's up and working great