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42-380 Tuning capacitor makes popping sound - Printable Version

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42-380 Tuning capacitor makes popping sound - Sourbone - 04-13-2016

I've successfully recapped and aligned a model 42-380. It works really well, but I can't find the source of popping when turning the tuning capacitor. I've blown air through it and brushed it out with a paint brush and cleaned it up with deoxit. It creates small pops as you slowly move it up or down the dial scale. I have replaced all the caps in this radio. 

Thanks for your help, 

Dave 

RE: 42-380 Tuning capacitor makes popping sound - NostalgiaRadioTime - 04-13-2016

I've had this same problem. Sometimes teeny tiny little spots of rust or corrosion develop between the rotor and stator plates of the variable capacitor, causing an intermittent shorting as you tune through the dial. You may need to take some fine sandpaper and carefully slide it in and out between the 'fins'. It can be a real bugger to find exactly where they are touching!

RE: 42-380 Tuning capacitor makes popping sound - Sourbone - 04-13-2016

Thanks, I'll give it go. 

RE: 42-380 Tuning capacitor makes popping sound - gregb - 04-13-2016

Sometimes that is really difficult thing to cure. As I do so many radio repairs I have invested in an ultrasonic heated bath and I run any tuning caps that need a cleaning or are noisy through the bath. They come out spotlessly clean and are perfectly quiet as well. I know not everyone can afford or even wants to invest in one but if you know someone that has one it may be worth a try and they look like brand new when done.

Gregb

RE: 42-380 Tuning capacitor makes popping sound - John Bartley - 04-14-2016

The other item that may be causing trouble is the electrical contact between the rotor and the capacitor frame. Sometimes a drop of oil in the bearing and/or on the rear point of rotation will clean the contact and get rid of the popping sound.

Some variable caps have "wipers" that do the job of maintaining the electrical contact. They can also benefit from both cleaning and lubing.

RE: 42-380 Tuning capacitor makes popping sound - Chris h - 04-14-2016

I have been using graphited lock lubricant, like "LockEze" on the contacts and non rolling element bearings on tuning condensers. Once applied, and the carrier evaporates, it leaves the graphite behind, thus no "wet" lubricant to attract dust and dirt. Has anyone else tried this technique? Are there any problems that you see with this type of lubricant? The fluid seems to penitrate and carry the graphite into the bearing surfaces.

RE: 42-380 Tuning capacitor makes popping sound - TV MAN - 04-15-2016

They have a ultrasonic cleaner at Harbor. Wonder if that would work for tuners?

RE: 42-380 Tuning capacitor makes popping sound - Chris h - 04-17-2016

I have the HArbor Freight ultrasonic cleaner ( with a heater). It has worked well for me. I even got the big tuning condenser in my Philco 95 in there. It took a couple of cycles, but managed to clean the whole thing. I use a little Simple Green and hot water. They have always come out looking like new. After cleaning I will place into a warm oven for a while to dry them out.

I would like to find a larger one that would hold the larger ones out of communications radios. Perhaps I will run across one one of these days. Icon_biggrin Icon_biggrin

RE: 42-380 Tuning capacitor makes popping sound - morzh - 04-17-2016

We make our own ultrasonic cleaner (uses acetone) to clean fibre. Small but the idea is the same. Though if Freight's one cheap I might buy that one.

RE: 42-380 Tuning capacitor makes popping sound - GarySP - 04-17-2016

Chris H, I would be very cautious using lock-ease, or any other graphite spray lubricant anywhere in the potential presence of electricity.  Any over-spray  would be very hard to detect, and the graphite could act as a tracking conductor.  Take care, Gary

RE: 42-380 Tuning capacitor makes popping sound - morzh - 04-18-2016

I missed the post about the graphite lubricant.....I'd be suspicious of it anywhere where electricity is present. If you are able to confine it strictly to the bearing, then fine.

RE: 42-380 Tuning capacitor makes popping sound - John Bartley - 04-18-2016

For the graphite lube, it would be an easy thing to spray it into a paper cup, then use a Q-tip to apply it to the cap?

RE: 42-380 Tuning capacitor makes popping sound - Arran - 04-21-2016

 Graphite is carbon, and carbon is one of the substances they make resistors from, so I would be reluctant to use in anywhere in a higher voltage electrical device such as a tube radio. This reminds me of the J.B Weld everything crowd on the alternative forum, J.B is metal filled, do you really want to use that on a tube socket or a switch, especially a band switch?
 I think that the main issue with the popping is that the plates in the tuning cap are rubbing just slightly, or there is crude on the wiper, or there is an issue with a grounding braid/strap such as it has a bad connection to ground or that it's rubbing against the rotor. Since the rubber mounts are probably shot anyhow you might as well remove the tuning cap and clean it.
Regards
Arran

RE: 42-380 Tuning capacitor makes popping sound - Sourbone - 04-25-2016

Got it. Thanks for your help. I emory paper and a tiny wire brush and got the remainder of foreign matter out of the tuning cap. It works perfectly now. Thank you.

Dave