Maybe a quick Electronics 101 might help. The capacitor (also called a condenser) will short any stray opposite voltage signals to ground. They have a polarity. Placed on a PLUS DC line and grounded, they will ground out any stray NEG voltage spikes (AC noise) that cause the familiar AC whine in the radio. Placed accost the points they will charge when the points break, preventing an arc.
however no where on wiring diagram nor on distributor indications does it even say that there is a cap in the 24vdc line,,,,,, just a curiousity thats all but then my manual is very limited and only covers what we called 2nd echelon maintenance in the corps, i was a electronic tech chief for 2nd mar divOriginally Posted by bmorgil
It almost looks like a redundant "points condenser" in your drawing. I can see however that it may have helped with radio noise. Everything was relatively low frequency AM band stuff and short wave in the WWII era. Any stray AC would wine for sure. The points opening and closing definitely would generate a little noise. Maybe the boy's were on to something!
Excuse me, Ma’am.
May I have a large helping of crow – without feathers if you have it. Thanks to everyone who looked at my drawing of the M38A1 ignition and helped me realize that it wasn’t correct. I hope it didn’t mislead anyone.
To reduce the radio interference in the M38A1, the engineers put ALL of the ignition stuff in a shielded box; the points, “condenser” and ignition coil. To prevent interference from crawling back out of the can onto the 24-volt vehicle wiring, they put the “capacitor” on the input to the distributor – which I believe is Wire # 12 in the harness.
Hopefully this is a bit more correct.
Wow the coil is inside the box! Something I didn't realize about the military distributor. That would be a great way to generate some RF!
You are an Artist no doubt.Your drawings both show about the same idea, an extra cap across the points.
The capacitor on the distributor input is isolated from the points by the inductance of the LV winding on the coil. I am pretty sure that the "condenser" is about 0.22 uF, 350 - 600 volt rating. I don't know what the "capacitor" value or rating might be, maybe someone will put one on a capacitance meter for us. It is probably rated about 200-volts or so.
Since that is a US Government contract vehicle, aren't the specs somewhere for the capacitor? Would that info be around? There are some Multi-Meter's with a capacitance setting, you could check a known good one. Of course if you had a known good one...
LarrBeard pointed out something. The noise capacitor is on the other side of the coil's primary winding. In stereo installs and what not it is common to put a cap on + supply lines. The bigger the better.
yupper, for one used schematics for the trc 75 ( a book) kinda wondered
am not going to coat the fuel tank inside, went to three places and enough material would be 300.00 us doillars
Last edited by pelago; 04-16-2019 at 01:09 PM.
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