I'm completely in the dark at this. What is the best, most effective way to discharge a capacitor?
I ask because I'm finally fooling about under the hood of the "trial" chassis (the 40-180 that will sit in my 40-190 cabinet until I can get the basket case '190 chassis restored) and on a whim, I tested the electrolytics with my capacitance meter...
...you can imagine my surprised when I found that the 16mfd took a charge. (22mfd, but there you are.
) Unfortunately, this now means I have a hot capacitor. Suggestions/techniques? The two books I have say to make sure you've discharged the capacitors but conveniently fail to provide a neophyte with the methodology.
put a jumper across the capacitor. If you want to be super fancy, put a 10K ohm resistor in series with the jumper and leave it hooked up for a few seconds.
I'd stick with the resistor, as a dead short against a fully charged electrolytic could damage it.
It is also a good practice to place a 200K or so 1 watt resistor across the first filter cap to "bleed" the voltage after the set is turned off. Still takes a couple of minutes, but capacitor won't recharge itself as some seem to do and jolt you when next you touch it.
Thank you for weighing in on this, gentlemen.
I'll put the biggest resistor across the capacitor that I have on hand, and it should be well and truly neutralized when I come back to it after my other duties today.
Can someone post a picture of what this "jumper" would look like (with or without the resistor). I want to create one of my own, before I start working on my radio (beginner as well) and I would like to see EXACTLY what people are using.
Additionally could someone explain in laymans term what exactly this means
"It is also a good practice to place a 200K or so 1 watt resistor across the first filter cap to "bleed" the voltage after the set is turned off. "
What is the first filter cap. Lets say in a Philco Model 48-200 ?
My goal is to be safe and I have been doing alot of reading, and alot of asking questions, before I attempt to tackle trying to recap my first radio.
Thanks !
A jumper is one of those wires with alligator clips on each end use for temporary hookups. You could attach one end of the jumper on the negative side of the capacitor, grip oneside of a 10,000 ohm resistor in the other jaw and then touch the positive side of the capacitor to be discharged. You may see a small spark. Hold it there for several seconds and you're all set. Of course this must be done only when set is unplugged!
If you look at the schematic, you will see the first capacitor in the B+ path from the rectifier.
Here is schematic for 48-200
http://www.nostalgiaair.org/PagesByModel...013627.pdf
The first capacitor is C101A which is attached to pin 7 (the cathode) has a value of 30 mf. I'd put a 200K or 220K 1 watt resistor there. Well this particular capacitor is ganged with C101B and C101C, but when you replace them, and you should before operating the set, you will use 3 discrete replacement capacitors as the multi section ones are no longer available.
The polarity is indicated in this schematic as curved line positive, straight line negative. Note the common negative is NOT connected to the chassis, as the B- common is not "ground."