Tone control For a Philco 91 (late) /14 - Printable Version
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Tone control For a Philco 91 (late) /14 - Capt. Apparatus - 05-01-2015
Hi everyone, I've got my 91 up on the bench for a general springtime checkup and clean out (found a spider inside
)Err anyhow, I'm having some "issues" with the tone control. It's Philco part number 06698 and while I've got it recapped and wired as noted in Ron's great cleaned up schematic I noticed in the replacement parts list in the Philco bulletin it gives Philco part number 04787 a four point tone control with a gradual step up in capacitance. Now the center three lugs on the 06698 are unused so most of the positions don't really seem to do anything, including to my ears the first parked position which runs to a few 100k resistors and a tin-box capacitor
So I guess I'm asking if I should Rewire it like a 04787 and see how it sounds or just leave it be. I would imagine they changed it for a reason either due to obsolescence or preference.
Advice and opinions would be greatly appricated
Schematic http://www.philcoradio.com/tech/images/1491.jpg
RE: Tone control For a Philco 91 (late) /14 - Radioroslyn - 05-01-2015
If you look closely at the tone switch the wiper ground three contacts at a time. So only the center position is the only one that is not connecting any tone compensation parts into the circuit. The first position should give you some bass boost. The 2nd will decrease the bass boost. 3rd will give you very bright highs. 4th will cut the highs some.
Terry
RE: Tone control For a Philco 91 (late) /14 - Capt. Apparatus - 05-01-2015
(05-01-2015, 09:56 PM)Radioroslyn Wrote: If you look closely at the tone switch the wiper ground three contacts at a time. So only the center position is the only one that is not connecting any tone compensation parts into the circuit. The first position should give you some bass boost. The 2nd will decrease the bass boost. 3rd will give you very bright highs. 4th will cut the highs some.
Terry
Thanks Terry! I'll double check my wiring over the weekend and give it another listen. For the control itself the fourth position you're talking about is the one with the single cap on it correct? When in the cabinet this translates to the most clockwise position, and how it was before the recap if I recall.
Of course there's always the possibility that my ears are just shot these days and everything's just fine
RE: Tone control For a Philco 91 (late) /14 - Radioroslyn - 05-02-2015
For the control itself the fourth position you're talking about is the one with the single cap on it correct?
Yup.
Terry
RE: Tone control For a Philco 91 (late) /14 - Capt. Apparatus - 05-03-2015
I double and triple checked my wiring and all that checked out a-ok I then realized that the volume pot in my 91 was a very, very old replacement made by CTS which got me to thinking on how everything's connected at the pot. On the schematic everything for the first 2 tone positions runs into a 2k ohm resistor which then runs to the volume pot's third lug however, on the schematic they're also showing a ground point just a hair under it.
Is the 3rd lug on the original philco control (part # 8054) not connected to ground or does everything just run into that grounded point regardless and am I just going insane??
If anyone can help make heads or tails of this I'd be much appreciated
RE: Tone control For a Philco 91 (late) /14 - Radioroslyn - 05-03-2015
Well maybe you are! No the important part is that the volume control has FOUR connection not 3. Should have 3 connections close together and a fourth around the pot a bit. The fourth one is a tap that provides a negative feedback point. Without it the set will work but no bass boost.
Terry