[morzh]

The 45 (butterfly) tone control's caps values are not shown in the BOM.

Typical values for several Philcos are 10nF,10nF and 15nF for three stage ones.
I inclined to think these are the same, 10nF and 15nF.

Another matter, I noticed that when using these values, the first stage takes out most of Hi and then the to others almost don't matter anymore.
Has anyone found optimal values?

[morzh]

OK, found my answer here
My values were close

http://philcoradio.com/phorum/showthread.php?tid=729

Good!

[Arran]

Mike,
I don't know why Philco insisted on using switches for their tone controls, it rather limits your options, in this case three positions but some only have two. The way they work is strange, they typically have three or four caps, one always stays in series, the other two or three are connected in parallel and are shorted out as you rotate the control, or vice versa. The one on my Philco 3118 has the shaft broken off so I have two options, replace with an aftermarket rotary switch and recreate the original hookup, or just junk it and put a proper linear pot in there.
Compare this setup to a Canadian Westinghouse console I have, it has a tone control pot, and a tone control switch. The switch gives you three ranges bass, medium and treble, and the pot allows you to adjust it anywhere in between. Did I mention that this was also a five tube console, shame on you Philco!
Regards
Arran

[morzh]

The way Philco does it is the caps are put in parallel to the primary of the interstage or output transformer, adding the next cap in parallel to the previous one. A bit of a brute force approach, I agree. The pot regulator should be in the grid circuit, not plate.

Anyway, I have rebuilt the regulator. Same thing as in 90 or 111, just no backelite box.

[Arran]

Mike;
That's a very common setup even with a linear pot tone control, which is one of the reasons why you should always replace the cap connected to to the center tap of the pot used in such setups. I've ended up with more then one set where the tone control pot burned up because that cap shorted to ground resulting in the full B+ flowing through it. One was so bad that it even burned up part of the Bakelite the resistive element was mounted to.
In the case of Philco if any of those caps on the tone control were to short it may take out the rectifier tube, field coil, output transformer, and even the power transformer since there isn't even a resistor in series with them. So basically what Philco did in this case is they substituted their three position switch ans caps for what would be the tone correction capacitor in another make of radio. Caps are cheap, inductors are expensive, change the caps.
Regards
Arran

[Ron Ramirez]

I don't know why Philco insisted on using switches for their tone controls

Marketing, I think. When Philco introduced their (four position) tone control in the 1930 models (June 1930), they made a big deal in their advertising of their "four point tone control...Brilliant...Bright...Mellow...Deep."

The switch gives you three ranges bass, medium and treble, and the pot allows you to adjust it anywhere in between. Did I mention that this was also a five tube console, shame on you Philco!