[dixierat]

My 38-116 chassis is restored except for magnetic tuning calibration.Problem appears to be subject switch stays in shorted position at all times. The contacts are not "welded" together and can be separated with an alignment tool.The switch seems to be a poor design in my opinion but there must be a way to make it work. Am I the first to have this problem? Please help before I fix it with a hammer.
Curtis

[Ron Ramirez]

If cleaning fails to correct the problem, an email to Mark Oppat may be in order...

http://www.oldradioparts.net/

The AFC switches on the 1937-38 Philcos are known to be problematic. These are often stuck in either the "off" or "on" position, or at least the part of the switch controlling the lights gets stuck in either the "off" or "on" position and will not operate.

[dixierat]

Ron, I previously cleaned the switch with deoxit but it did not adequately clean the contacts. So your reply prompted me to use a very small file to brush the contacts. Now the switch works perfectly. Magnetic tuning was easily aligned and 2 stations were set to be tuned using the magnetic tuning feature.Seems to work as Philco intended. Thanks,
Curtis

[Ron Ramirez]

How small a file did you use?

I never thought of that. Great idea.

[Chuck Schwark]

A relay contact burnishing tool is what is the least "aggressive" for those types of open conacts,
as compared to a small needle file.
I use one with a SMALL drop of De-Ox-It contact cleaner on it. Lightly push the contact leaves
together on the tool and 3-4 in and outs with the contacts held closed usually does the trick.

YMMV

Chuck

[Ron Ramirez]

Chuck

Where would one obtain one of those relay contact burnishing tools?

I have a 40-201 with a pushbutton assembly that is giving me fits. Two of the buttons only work if you hold the button in while holding your mouth just right.

[codefox1]

A long time ago we used to use a fresh $1.00 bill as a burnishing tool, whilst squeezing gently with a a needle nose pliers. I seem to remember the old master applying a little denatured alcohol before the procedure was performed, an the crud removed from the switch and a tiny amount of lithium grease placed on the shaft. Mind you what was before WD-40 and Deoxit. We used more ridiculous substances in those days to clean things.

[dixierat]

I used a flat needle file from a set purchased from RS. A drop of deoxit on the file as suggested by Chuck is a good idea but I did'nt think of it.A burnishing tool would be a welcome addition to my tool drawer for use on the next sticky switch.No electronic background here so I don't know where to get one. If I get one I'll store it next to my hammer.

[Chuck Schwark]

I'd order a few:

MCM Electronics (no min orders too!)

GC Electronics Part #: 9337 | MCM Order #: 22-910

http://www.mcmelectronics.com/product/GC...37-/22-910

[dixierat]

Thanks Chuck, I just ordered 5 so I'll be ready for the next dirty open switch.

[Ron Ramirez]

Yes, thank you, Chuck; I too will order some in the near future.

[Chuck Schwark]

You're welcome guys. I use them at work (broadcast tv equipment) on control relays, circuit board socket contacts, switching contacts on 1/4" phone jacks, analogue audio patch bays, etc. The drop of De-Ox-It and the tool keeps 'em running fine.

Chuck

[codefox1]

Agree with all. Now, Philco sets probably didn't have switches plated in silver or gold, some equipment did. That's why the very conservative methods were used in the past. If we're dealing with copper contacts encrusted with mouse pee that have lost their tension and sticky shafts, or busted bakelite that needs to be clamped and crazy glued together that's one thing. Switch contacts, just as tube socket parts are sometimes possible to be replaced by donor parts from junkers, but this often involves rather delicate operations to clear the offending area, remove he existing piece, and replace it, and finally epoxy it in place and wait a day or two while it sets up and cures. And eventhen the operation may be successful but the patient dies, but that's how it is.

[BDM]

I use thin emery nail boards (very very fine), or emery cloth. Works like a charm.