1947 Special Radio

[Jack Worstell]

We have a factory radio in our 1937 Special.    The manual says to install

 

        a capacitor on the coil primary ( + terminal )

               and

         a  suppressor ( resistor )    on the center   pole of the distributer cap

 

But it says nothing about what the size capacitor (  in micro farads I guess ) should be  nor how many ohms the

suppressor should be.

 

Can anyone help on this ??

 

Where can I get the right suppressor ??

 

Jack Worstell

 

PS   the manual also says to put a capacitor on the generator....but we have an alternator...

does this also require a capacitor?  If so....how many micro farads ?

 

 

 

 

[Daves1940Buick56S]

The capacitor for the coil and alternator should be about 1 ufd. I would get a voltage rating of at least 50 vdc to be on the safe side. The resistor should be abt 5k ohms, but if you are already using R plugs and resistor wires leave it be. Do you have a lot of static interference that goes with the rpm?

 

Cheers, Dave

[Bloo]

Spikes at the + terminal of a coil on an older 12v car can be well over 200V. A 50 volt rating on a capacitor sounds too low to me, even for 6 volts.

 

Typically these capacitors, as originally used, were metal-shelled things specifically made for the purpose. They look about like the condenser that goes in your distributor, but have a tab (sometimes welded on) so you can attach it (and ground it) with one of the mounting bolts for the coil bracket. They were dirt common through the 80s at least. I would see if NAPA has something appropriate.

 

 

Edited February 8, 2019 by Bloo (see edit history)

[Daves1940Buick56S]

Hmmm, I have a full ignition test bed on my bench, I will check.

 

Cheers, Dave

[Jack Worstell]

Thanks for the info everyone.

 

These things are surprising not that easy to find.   When I do find them ( eg NAPA )

they don't give specs for voltage rating or for capacitance.

 

Jack Worstell

[1937 Buick 66C]

Good Afternoon Jack et al,

 

We need to keep in mind that the use of AM radios in automobiles and associated interference was still in it's infancy in 1937.  There was not a comprehensive understanding of what aspects of the automobile would cause radio interference, therefore they approached it with an abundance of caution and seemed to install capacitors all over.  I suggest putting the radio in the car, get it working, and see if you can hear any interference from the systems in your car (pops from the ignition, or a whine from your alternator).  I had my radio rebuilt, put it in, and do not have any interference from anything so no capacitors at all.

 

My brother-in-law has a very original 1937 Century sedan, and there are capacitors everywhere.  They're on the ignition (coil), light switch, generator and one on each running board between the running board and the chassis.  His radio does not operate, so we've never investigated whether or not there's any difference in the way the radio behaves.

 

A good car audio store will have several types of noise suppression capacitors available;  They're probably your best bet for obtaining one.

[Bloo]

The things he asked about were standard equipment as long as cars had conventional distributors and coils.

 

After a while, the resistance was no longer a separate "suppressor", it was just moved into the plug wires, making the suppressor attachment redundant. Today, there is also resistance in the plugs themselves (whether you want it or not).

 

The capacitor on the coil never went away until the coil did. There is likely capacitance in modern systems doing the same job.

 

The capacitor for the alternator is probably already there. It is usually mounted inside.

 

 

Edited February 9, 2019 by Bloo (see edit history)