[ntsc525]

Thank you for pointing out the tone control link, as that was very helpful!

I interpret the tone control chart to give the EFFECTIVE capacitance provided by the switch for each position, since I believe .035 is a pretty high value for a tone control. So, we have to figure out what the switch does and how the caps are wired to see how the switch provides those values in the end.

So, I dug out the tar and tried to measure the values of the caps and figure out how they were connected.

My only good reading was .015 before I dug the tar out. I think it was the first position, which likely turned out to be the first two caps in series before I dug them out of the tar and ruined everything. (Now they are all open.)

Position 0 is off. (Switch is open to ground)

Position 1 is actually 2 caps in series. (The middle lug has 2 leads soldered to it.)

Position 2 is the middle cap direct (series cap is shorted / bypassed)

Position 3 is middle and third cap in parallel, because those two are tied to the common going back to the Audio output.

It is possible, even likely that my first (only good) measurement was been looking at 2 caps in series when I got the .015 (After I pulled them out of the tar to discover how they were wired, they were all open.)

Assuming the capacity ranges given for the tone control represents the effective capacity, then I have to figure out how to get those values based on the first two in series, the second one being .025 (.022 now), and the third one being .01 to add up to .035 when connected in parallel with the middle one.

I think perhaps a lot of people get confused by the capacitances given in the chart, thinking each individual cap has to be the value given, and not realizing what's under the tar. Examining the switch more closely reveals the series / single / parallel arrangement. If you just installed the given values for each, the third position would be a total tone killer (.06 uF).

So, using the series capacitor calculator at Digikey, (algebra, at my age?!!), and plugging in modern cap values, I came up with the following modern capacitors that will get close to the original:

C1: .047
C2: .022
C3: .01

So, the effect is:

Position 1: = 1/(1/C1 + 1/C2) in series, giving .0149 (Target: .015)
Position 2: = C2 with C1 bypassed, giving .022 (Target: .025)
Position 3: = C2 + C3 in parallel giving .032 (Target: .035)

Anyway, this is close enough and what I'm going to try!

It'll be a while before I hear how it sounds, since I started with the tone control so I could mount it after painting the chassis, and there is a lot of kluge work I have to untangle.

Thanks again for the help!

Dan