Old C1 Capacitors

[Mike G.]

From time to time, someone will post a question about what the capacitance values are of various caps in C1s. Apparently, original caps are fairly easy to come by. I'm wondering how close to original specs these old caps are.

With old (50s, 60s and even 70s) guitar amps or recording consoles, replacing caps (with equal values, not hot-rodding) is pretty common and my own ears will confirm that the improvement in sound is very noticeable. Apparently caps go bad over time. Replacing resistors or transistors is NOT routine like with caps (and certainly tubes) with vintage music gear.

I realize original appearance is more important than removing ALL the engine whine from a Wonderbar (the primary purpose of the capicitors behind the guage cluster), so I'm not saying original caps shouldn't be used. And possibly the TYPE of caps in C1s keep their values? I'm just wondering out loud. Any thoughts?

[John M.]

Re: Old C1 Capacitors

Mike,
I have a capacitor tester and allways check them before using them or selling any to my friends. The rating of all the cap's are shown on the outside of the case. an open cap would not cause any damage, but not so for a shorted one. The worst thing that is going to happen if it is open is the radio is going to be a little noiser than normal.

Regards, John McGraw

[Dave K.]

Re: Old C1 Capacitors

John,

I'm putting my C2 66 Corvette back together and was wondering how to check all of the capacitors (stop light switch, instr. cluster, coil, blower motor, etc.? I have a Fluke digital voltmeter and thought that I could at least check for an open or short circuit. Any thoughts? The stop light switch capacitor, located on the pedal cluster, has both terminal ends cut off and I was going to replace it but Long Island doesn't stock it. I'll check my new electrical harness to see waht kind of terminals it will require and plan to reuse it. I believe that it is wired in parallel with the switch.

Dave Kitch
33108

[Mike G.]

Re: Old C1 Capacitors

I've now been told that the capacitors that lose their specs are generally the wax-foil type, which are inside the Wonderbar radios, but not the ones at the back of the guage cluster. So my concerns may have been exagerated.

Apparently, there are two things to check for in a capacitor: capacity and dissipation (I ain't the expert here, so feel free to correct me.) Capacitance is how much charge it holds and dissipation is how much leaks from a held charge. A standard multi-meter should be able to check capacitance (expressed in farads?), but I'm not sure about dissipation. The wax-foil (no longer made?) capacitors develope dissipation problems as they age.

[Bernard M.]

Re: Old C1 Capacitors

John, I also have a meter that allows me to test for capacitance values and use it to test old Delco-Remy capacitors I might use. Their rated capacitance value is stamped on the end. I've always assumed these ratings are +/- 20 percent (standard electrical tolerance). Do you have any idea what the voltage rating of the capacitors is? I'm guessing spikes at positive coil terminal could be over 100V and somewhat less at the generator and voltage regulator. Do you (or anyone else) know what the voltage specifications are?

[Jack H.]

Re: Old C1 Capacitors

Specs vary by specific component (tolerance and working voltage rating). You need the applicable document(s) that define the parameters. Wax foil caps will typically have both specs published on the body. Mica caps use an industry standard color coding convention. Most electrolytics used for 'boat anchor' RF supression were 'sloppy' with +/-20% tolerance and somewhere around 200 VDC working voltage.

But, why would this (specific rating) info be of any use? The external RF caps had Delco Remy marks on 'em and that's what's important in a factory concours judging setting. Trotting on down to Radio Shack to find a generic replacement is of little value to most on this board....

The benefit(s) these RF suppression caps brought to the car were marginal in the first place. You typically needed to be in an AM 'fringe' reception area to observe a difference (cap present or cap absent) and most of the daily driver applications I've seen restrict their classic Corvette, weekend warrior, jaunts to not straying too far from major metro areas.

[John M.]

Re: Old C1 Capacitors

Dave,
Although it is not possible to find the capacitance value with a standard VOM, It is possible to at least tell if it is working at all. First, you would check the capictor for shorts, and it should not show low resistance in the check. Then you should lock the meter into a high range like 100k ohms or greater and check resistance in one direction. After doing this you should reverse the leads and you should see a quick spike on the meter and then it should drop back down again. You are charging the cap in one direction and then discharging it through the meter in the other. This does not indicate anything other than the capacitor is working to some extent and is not open or shorted.

Regards, John McGraw

[John M.]

Re: Old C1 Capacitors

Jack,
You are right on the money! The numbers are what's important, and it isn't like there is anything left to listen to on AM radio anyway.

Regards, John McGraw

[Bernard M.]

Re: Old C1 Capacitors

Jack / John, Actually it does have a bearing on RESTORATION. I've been able to repair other electrical components to factory specification by substituting internals with updated parts (I'd be happy to share my chapter newsletter article on repairing e-brake flashers). It would not be difficult to repair a generator capacitor (for example) that is rated at .5mfd by using a standard size .47mfd capacitor inserted into a hollowed metal Delco-Remy case. An end seal canibalized from an old distributor capacitor, some solder and voila, a fresh part. But to do it right, one should know the voltage at which the capacitor is rated.

[John M.]

Re: Old C1 Capacitors

Bernard,
I would not disagree with restoring valuable old electrolytics when necessary, and I have done so on some multi-section electrolytics from old radios as it is impossible to find NOS Delco units. In this case it is easy to insert new components in the case and close it up, as the modern components are a fraction of the size of old caps. In the case of suppresion caps, they are pretty widely available if you are willing to scrounge through junkyards and the time spent taking one apart would not be time or cost effective. The bigger difference as Jack and I both were pointing out is, that even if they were not working, nobody would probably know the difference. On a Radio Electrolytic capacitor, if it does not work the radio does not play.

Regards, John McGraw