Quiz on capacitors

poorguy · 13 Jul 2014

wow thought I was the only one left that liked tubes. I still repair old tube electronics mainly old farm radios and table radios. lots of old wax paper caps that need to be replaced in most of them. for me it is a return back to a time when things were made to last and be repaired and made with pride and quality instead of the disposable crap produced today.electronic repair shops are a thing of the past. most parts can be found online but I sure miss the old electronics parts stores with all the surplus parts and the knowledgeable people who worked in them unlike the dumb asses that work at radio shack. vom/vtvm/oscilloscopes/rf signal generators/condenser testers/tube testers yeah that's real electronics and I am glad that I was able to live it and learn it because it is a time that will never be around again because progress has made us into a disposable society. just the way I feel. thanks for the space. poorguy

poorguy · 13 Jul 2014

hey all, yeah I will agree modern capacitors do cause a lot of problems because of their design and where they are placed. in power supplies caps sometimes are placed near transistor heat sinks which dissipate lots of heat and most of these caps die due to the fact that they can't endure the temps they are around. poor design and cheaply made components. I replace lots of old wax paper caps in tube radios but hell some of them are 40 to 50 years old. I have stacks of brand new motherboards that need to be recapped and have never been powered up yet just made with cheap components. it is pretty bad when name brand boards come with swollen capacitors installed on them. can't complain to much though because I make good money from recapping motherboards for my local computer store. just some more of my thoughts. thanks for the space. poorguy

M1GU31 · 13 Jul 2014

7/10

Then again I have little knowledge on the subject since I haven't really looked at it but learned some stuff even though I knew some of it already. Missed 3 not too bad I guess though it's like C eh.

poorguy · 13 Jul 2014

well I just took the capacitor test and missed the last question about the jar. ok test did not know that. good history. poorguy

ICIT2LOL · 13 Jul 2014

Hiyya poorguy like you I had a bit of experience since I was a young bloke but never so much with radio frequency stuff my interests lay in audio and still do.
A component we all have known can be the problematical child in the device and underrated as a potentially dangerous one too.
Not just form the charge that they can deliver but also as I discovered many years ago capable of delivering bomb like physical injury after connecting two large paper types in a stereo amplifier I had made and connected the two large smoothing caps the wrong way round. The resulting explosion showered me and my bedroom with shrapnel and that awful electrolyte muck, no need to say it destroyed the stereo unit as well - not a tube left standing!!
The jar mate is really working on the same principle as the lightning by the by.
I know that some devices work by any material body that comes close to a detecting device ie a stud finder work by detecting the difference in in capacitance that the proximity of a solid body produces in the device.
That is to say that when the device is dragged across the wall when the stud behind the surface passes under the detector the capacitance in a part of the circuitry is altered and is then "computed" as an anomaly and indicates that change as a signal to let you know the stud is at that point.
Similarly I would hazard a guess that some touch screens we use today work along the same principle - will have to check that one out.

poorguy · 13 Jul 2014

hey ICit2lol, yeah that not getting the polarity right is a bad thing but a good learning tool. I have worked on a lot of audio equipment as far as amps also tv and radio and capacitors sure seem to be the cause of a lot of failures in them. in high school we made a tesla coil using a pole transformer and made a capacitor using tin foil and ceramic floor tile in a clay pot it was interesting. as far as the charge that caps hold in equipment a lot have bleeder resistors tied across the caps to drain the voltage out of them. rule of thumb is keep one hand in pocket when working on or with any electronics. I will always test caps with a volt meter 1st though. don't know much about the touch screen monitors other than they are used a lot every where. yep things sure have changed. poorguy

Lady Fitzgerald · 13 Jul 2014

The tesla coil my Daddy and I built was made from a neon sign transformer we found at a salvage yard. The capacitor for the air gap oscillator was made from aluminum foil and several panes of window glass salvaged from several multi-paned windows I found in an alley. I hand wound the HV coils with magnet wire on cardboard carpet tubes that I shellacked the snot out of. It not only put out a quarter of a million volts, it disrupted TV reception for the entire block.

Daddy once salvaged a couple 12v 1 farad capacitors from a trash can at work. I had a lot of fun with those. The only thing I ever blew up was a 12v automotive ignition coil. I had hooked it up to 120v AC to see how big of a spark I could draw from it. It worked great...for a short while. When the oil or whatever it was inside got hot enough, it blew the top off and left a rather conspicuous spot on the ceiling of Daddy's work shop. I had hoped he wouldn't notice but he did that same day. I still can't believe that I got off with nothing more than a mild chewing out.

ICIT2LOL · 13 Jul 2014

Yep poorguy it is a real learning experience and I used to (foolishly) show my nephew what happened to electrolytic caps when connected the wrong way round - only small ones but still daft. By the by he went on to become an electrician and now designs electrical systems for MacDonalds and KFC etc etc So my "training" must have done some good LOL!!
The screen stuff I went looking and found out a bit like this HowStuffWorks "iPhone Touch Screen" and this one that mentions the human body
Capacitive Touch Screens

Jeannie that must have been quite a bang as I can imagine that primary coil taking a hell of a pasting before melting down the discharge from the secondary - one wonder what that would have contained

I also found an enormous IBM machine dumped at the local tip years ago before they stopped you picking the tip over and it contained some caps in it that were enormous one I seem to remember was 5 farads and many that were over 1 farad and in hindsight we were playing with some seriously dangerous devices eh?

A bit OT but the plate drives from microwave ovens if you take it out and spin the inner drive (plate deck) round (very hard to do but possible) the motor generates around 400 volts !! Kicks with a punch and I was trying to figure out a way to make a generator by spinning that plate driver with a windmill and use an inverter to use the output in battery charging.
Microwaves are very interesting things to disassemble as there are so many parts that are so useful:)

John

poorguy · 13 Jul 2014

hey Lady Fitzgerald, we used to use neon sign transformers and welding rod to make Jacobs ladders. the welding rod didn't burn up like copper wire. seems like we had to make coils from cardboard tubes also for our tesla coil. I know we caught a lot of hell for the tv interference also not to mention the power problems we created at times. yeah we used to blow up caps also just by reversing the polarity of them it was fun. the fun days of youth. I got into electronics as a 10 year old child, had an interest in ham radio and thought morse code was cool so I learned it and managed to get a novice license and that is where I got started. don't mess with the ham radio much anymore although I still have the license and a 2 meter rig. yeah we used to take power transformers and pulse them with flash light batteries and find someone to hold onto the wires, but they didn't for long haha. good old harmless scientific fun. poorguy

ICIT2LOL · 13 Jul 2014

Hmm sounds a bit like the stuff my nephew and I got up to like soldering on a wire to the high tension on the cathode ray tube connections and then touching around inside of the set (an old one of course LOL!!) with the wire end and watch the light show