The PHILCO Phorum
4 position tone control 90X - Printable Version

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+--- Thread: 4 position tone control 90X (/showthread.php?tid=17814)

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4 position tone control 90X - patrician56 - 01-21-2018

Work proceeding with the 90X restoration. Bakelite cap blocks re-stuffed as well as the metal cap box. Now I face a new issue with the tone control. 4 position metal housing switch – off and 3 additive levels of tone.
When I took the chassis out of the cabinet, I noticed a tarnished thin metal disc (approx. 5/16” in diameter) on the shelf below where the tone control was mounted. Examining the underside of the chassis, I saw where the disc used to be attached. It was one of the contacts on the tone control. The stem where the contact broke off looked granular, like the metal was stressed. The second contact fell off while I was removing the tone control. The metal at the break point also looked granular. The third one is still intact, for now.
Are contacts breaking off on the tone control a common occurrence? If so, any tried and true fixes?
I was thinking of filing the head of a small machine screw down to the thickness of the contact, drilling out the remains of the riveted stem and attaching the assembly with a lock washer and nut. Any other ideas?
Thanks very much.
Fran

RE: 4 position tone control 90X - morzh - 01-22-2018

Fran

I have rebuilt several Philco radios that use this or very similar type of Tone control, including 90 and 70 models.
This is the first time I hear about this defect having occurred. The effort of the sliding contact moving across the contacts' caps is very light.

Well, in the worst case for a while you will have to operate the radio without the tone control, it will just work at the peak of the treble transfer; when you locate the new control or fix this, you could install it.

RE: 4 position tone control 90X - patrician56 - 01-22-2018

Thanks very much,
I look upon this as a challenge accepted  Icon_biggrin

RE: 4 position tone control 90X - Radioroslyn - 01-22-2018

If you are not trying for correct restoration you can swap the switch for a pot (.5 meg-1meg) and a cap (.05 @ 630v). This will give you a variable tone control.

RE: 4 position tone control 90X - patrician56 - 01-22-2018

Thanks Terry,
But I think that I am probably looking for another 4 position switch to rebuild. I want to keep this set as original as I can.
Fran

RE: 4 position tone control 90X - Arran - 01-23-2018

I like the brass screw idea for a repair of the broken contacts, get the type with a standard slot, not the Phillips style ones, and if need be you could fill in the slots with solder. People used to build home made rotary switches this way back in the 1920s so I can't see why it would not work here. I never like the rotary switch tone control idea that Philco went with, it seems kind of crude, I don't know why they used them unless it was because they could avoid paying royalties to someone, or because they could make the switch assemblies in house but could not do so with potentiometers.
Regards
Arran

RE: 4 position tone control 90X - Phlogiston - 01-23-2018

Never seen one broken like that. I would probably just solder the contact back onto the brass lug.

RE: 4 position tone control 90X - EdHolland - 01-23-2018

I might have a 4 position switch in a box of bits I bought for my 16X restoration. Let me look and see if it matches.

RE: 4 position tone control 90X - patrician56 - 01-23-2018

Thanks Arran,
I drilled out one of the broken riveted contacts. Looks like a #6 round head brass screw might work. However, the actual contact is very thin, so duplicating that would probably mean removal of most of the screw head...Lots of filing or machining. That's when I thought that I would place an ad in the Phorum want ads (I did) and see if someone had one for sale. If no luck, then try the brass screw route.
Fran

RE: 4 position tone control 90X - patrician56 - 01-23-2018

Hi Phlogiston,
My original thought was possibly to solder it back on, but there is not much room to work under the contact, and the connecting wire grommet is part of the sandwich, so my second thought was something mechanical, hence the brass screw.
Fran

RE: 4 position tone control 90X - patrician56 - 01-23-2018

EdHolland,
Thanks for offering to look see if you have one. 
Fran

RE: 4 position tone control 90X - EdHolland - 01-26-2018

Not forgotten - I just haven't had chance to get to my box of bits yet. I'll try and snap a pic this weekend.

Cheers,

Ed

RE: 4 position tone control 90X - Arran - 01-27-2018

See if you can find some brass pan head or oval headed screws, the heads are flatter to start with so there would be much less to file down then a round head.
Regards
Arran

RE: 4 position tone control 90X - patrician56 - 01-28-2018

Ed,
Thanks very much.
Fran

RE: 4 position tone control 90X - EdHolland - 01-28-2018

Fran,

I dug out the switch just now and took a couple of pictures. It is in good mechanical shape. Caps are original to the 5 band model 16 from which it came.

   

   

If this works for your radio, let me know and it is yours.

Cheers

Ed