C-2 AM/FM Volume Control

[Gordon Peterson #4961]

Hi all -

My AM/FM was a mess, and among other things, made a severe noise whenever I tried to adjust the volume. Last year, I had the radio gone through by a professional. The radio now works very well, but I was told that the volume control noise is irrepairable, and replacement volume controls are rare as hell. So for a year now, I would preset the volume, THEN start 'er up, and I've been enjoying my radio - just don't touch that volume control!!

With diligent searching, I've found a replacement volume control. My original is p/n 7282024. The replacement is p/n 7290296 which I understand is made for a later C-2 radio, but is functionally identical and nearly identical in appearance.

I've pulled the radio and the old volume control. This was going to be nearly a one-for-one swap except for one area. The base of the original has four lugs wired as follows (c/w from the top in my image):
red (power? - wire comes from the radio power plug)
white (goes right to the radio lamp)
black (goes to a nearby choke and has a resistor in parallel)
brown (also goes to the power plug)

The replacement control also has four lugs. But they are oriented in a different pattern, and it is not clear which wires go where. This is where the power gets distributed to the radio, and I sure don't want to mess it up.

I've attached a photo comparison that shows some cryptic stampings in the base of each that might give a clue. I'll probably play with an ohmmeter to see if there are any electrical clues.

Meantime, can anyone help me figure this out? My radio and I thank you!

Pete

[dick foehringer]

Re: C-2 AM/FM Volume Control

they are 2 separate swiches in the control. one has power directly from the connector on the outside and that goes to the light. the other is power thru the noise filter/choke. it powers the radio. you will just have to ohm out the 2 separate switches and hook up accoringly. the worst that will happen is that your radio will come on when you turn the lights on!im really surprised they couldnt clean the control. i have a special lube/cleaner that fixes the scratchiness. unless maybe your control wiper resistor is cracked. that will make it jump way up in volume when you hit that point. let me know if ou cant get it hooked up.
regards dick

[Gordon Peterson #4961]

Re: C-2 AM/FM Volume Control

Hi Dick -

Ohming these out was inconclusive - I'm still not sure what I've got, and I'm going to have to think about what I see here. Plus I see that the ohm range for the volume section is 0-21K ohms where my original is 0-7K ohms. I'm not sure of the effect that would have.

As for cleaning, here's what the restorer told me:

"I'll try to clean the control although it appears someone else must have used WD-40 on it already. A bulletin was issued by Delco a while back against using that type of solution as it can accelerate the delaminating of the carbon film on the controls manufactured after 1960. The cleaner I use evaporates quickly and costs $35 per can."

So it sounds like he's already tried to clean it, and trust me, it sure didn't work! OUCH!

But here's a word of warning for others with noisy volume controls!

Pete

[Gordon Peterson #4961]

Re: C-2 AM/FM Volume Control

If anyone is following this thread, and I understand this is a common problem, here are some answers.

I have spoken to my radio restorer. If you view the base of the original control (left one in the image), let's call the top lug A, then B/C/D going clockwise. The "L" between A/B stands for Light (power to the light), and the "R" between C/D stands for Radio (power to the radio). And with the switch turned on, lugs A/B and C/D are shorted.

On the NOS replacement control, the upper left lug is the A lug with B/C/D again going clockwise. I have confirmed that A/B ("1" is for light) and C/D ("2" is for radio) are shorted with the switch on.

Further checks can be made. Across the end terminals of the top tone control section should read 100K ohms (+/- 20%). Across the end terminals of the center volume control section should read 20K ohms (+/- 20%). You should also read 6K ohms from an end terminal of the volume section to the lower tap on the volume section. My original is out of spec on the volume section.

We've also found a bad capacitor on the tone control terminals that, after all this, "might" have been the cause of the noise. I'll replace it surely, but I'm going to install the new control because I don't want to have to do this again.

Pete

[Joe R.]

Re: C-2 AM/FM Volume Control

Gordon,

Use the top two for your red and white wires (one to the lamp). Use the bottom two for the browns. This will work if the switch is good.

Regards,

JR

[Gerard F.]

Re: C-2 AM/FM Volume Control

Gordon,

I think you've got it figured out but I thought I'd confirm that the switch 7290296 was the original part number for a 1967 and is probably the same for a 65 and 66. I replaced mine a couple of years ago and I was lucky to get an NOS one which looked exactly like the one I took out, and looked exactly like your original one (on the left in the photo) with the R&L. The wire colors may be different in later years.

The four lugs on the back are just like a double pole switch which turn on two circuits, one for the radio and one for the light. However, be sure that you are not reversing the feeds. The light is fed from the instrument light circuit, and dims with the instrument light from the headlight switch. The radio is fed through the radio circuit from the fuse block. If you reverse the feeds, you will be blowing your instrument light fuse, and will find it impossible to dim the radio light.

I think you have it figured out but just make sure you've got the right feed to the right circuit.

Jerry Fuccillo
#42179

[Gordon Peterson #4961]

Re: C-2 AM/FM Volume Control

THANK YOU, Gerry! I really appreciate that input. And you can bet I'm going to figure out some way to test it before I go through the aggravation of putting this puppy back in that dash!

Pete

[Gerard F.]

Re: C-2 AM/FM Volume Control

Gordon,

Happy soldering! While you have it out, check the board and innards for corroded soldered connections and solder them up also.

You can bench test the radio with a battery charger, replacement speaker, and a gypo antenna. I think your restorer is probably right about cleaning it once too many, and dissolving some part. Once it's worn it's worn, use the new one. I'm not so sure it's one of those two capacitors soldered to the switch, it wasn't with mine. I resoldered them onto my new switch and everything worked fine, no more static.

I have the wiring diagram and the parts lists for the 65-67 AM/FM. Email me if you need any info from it.

By the way, my NOS switch cost $75 from corvetteradios.com

Jerry Fuccillo
#42179