need help

[bob91343]

Okay I found a web site http://www.calculatoredge.com/electr...low%20pass.htm that will calculate it for you.

I tried it, selected 8kHz and 1500 Ohms and three components, and got two 0.44 microfarad capacitors and a 21.2 Henry inductor. Oh and I selected 3 dB ripple, sort of arbitrarily.

[radio nut]

Thank you, you are obviously electronics trained or understand far more than I do. I really am trying to learn more about how a radio works instead of just being a cap replacer and resistor checker. Sometimes it is hard wihout a teacher..... I just can't raise my hand and get the answer I need. So When I do get a book sometimes it helps me sometimes not.......

[bob91343]

If you are serious about learning electronics, you need to make a plan. You could go for a BSEE but that's kind of ambitious; perhaps a technician course would be better. But they don't have them the way they used to. One of the old courses from CIRE or Sprayberry or National or DeJur would be a possibility. Browse the web.

Sit quietly and read from page 1 in a basic textbook. Read the first few pages over and over until it makes sense. Do some experimenting. For instance, get an Ohmmeter and measure a few resistors. Calculate what resistance they would be in series or in parallel and then measure them that way to see how you did.

Humility is important. There is no end to the learning process so don't look for results, just understanding. Read the Radio Amateur's Handbook, for instance. Over and over.

[bob91343]

A few posts up I think I mentioned DeJur but what I meant to say was DeVry.

[radio nut]

Ok, I have probaly repaired over 100 radios and 5 b&w tube tv's now. With an occasional exception I am getting better at diagnosis. With my Capehart 21n2 I had a distortion problem on am and fm. Knowing that it has seperate fm and am up to audio I figured it was an audio problem Knowing that the paper caps in the bass switch were replaced I looked the diagram and figured it was one mica tied to the volume control.....and was right. It works well now. The owner of Fair Radio here in lima can look at a diagram and tell you what exactly each cap is doing and why. The man just blows my mind with his knowledge.

I have been there when a technician couldn't figure out what was wrong with a military transceiver and handed the diagram to the owner... he looked it over asked what was going on and said check this transistor or whatever part it was and sure enough was right. I guess it may take me a LONG time to get there but WOW..... thats what I want.

[radio nut]

Maybe I am trying too hard !

[bob91343]

Just accumulate knowledge and experience. Nothing else will do.

I too can diagnose without seeing the gear; I have done it many times. And yes, I can tell the function of each part, and even critique the design. And make suggestions for change.

Electronics has been my hobby and vocation for 70 years or so. I am always learning something new.

[radio nut]

thank you for your help. I love all things old and wish I had grown up back then with the tube radios and tv's. old cars...........you name it.

[DavGoodlin]

Most of us who did this back when good old stuff was tossed thought we were the only ones who cared. Now we know there are others, of all ages, who can learn the art of conservation.

[radio nut]

I just hope as an example with my pride and joy Capehart by Farnsworth 21n2 that as much as I play it that tubes will still be available and not cost and arm and a leg when I am old.
Yes some are being made new now but 30 years from now who will have a 6af6 tuning eye or 1l6 for the Zenith sets? are all the tubes we need going to be out there?
What about crt's..... will the color roundies be out of luck?

If I would ever hit the lottery I would love to start making some of these hard to find items like the early color crt's.......but is it financially possible now?

[Reece]

Some of the rarer tubes will get harder or impossible to find but there are ways to adapt to others. Whenever this topic comes up the fact is raised that millions upon millions of tubes were made during their heyday and caches of them are still being discovered, so there's a likelihood that most common tubes will be readily available for a couple of lifetimes.

As to learning about radio, there's nothing like reading to understand, and experimenting. There are many ways to gain experience but as a kid I scrounged old junkers and used the parts to build sets copying schematics out of books and Popular Electronics. My uncle and I built a crystal set, not a very good one, that picked up two locals, when I was in the third grade. After that I got into working with tubes. I never could get a regen to work. Finally one day that I remember vividly it squealed into action and was picking up DX. I ran outside my shack around the yard exulting: I felt like Armstong himself!

One good way is to take a simple working set like an AA5 and go through it with a signal tracer, following the signal stage by stage. If you don't have a signal tracer you can make one quickly using a spare amplified speaker left over from a previous computer, making up a couple of probes: one for AF and one with a germanium diode for RF. One site that I have quoted frequently takes you through an AA5 and I think is helpful as it explains each stage in turn so the whole mysterious thing is not staring at you all at once. Some may want to bookmark or print out this site:

http://www.angelfire.com/electronic/...bes/AA5-1.html

[bob91343]

You can use a second AA5 as a signal tracer. Just use the hot side of the volume control as a probe and, if you want rf, add a diode.

Just watch out for those hot chassis jobs! An isolation transformer is a very good adjunct to your shack if you're going to work on this stuff.

[radio nut]

I do not understand the reason for the line isolation transformer.... the set is still powered up so what is the difference?

[bob91343]

The isolation transformer makes the gear safer for the technician. In the nonisolated set, one side of the power line connects to the active circuitry and, sometimes, also to the chassis. This is not a safe situation. The danger varies widely depending on the orientation of the plug to the power line; one way is asking for trouble, the other may be safer until you connect a second unit.

[radio nut]

Originally Posted by bob91343

Just accumulate knowledge and experience. Nothing else will do.

I too can diagnose without seeing the gear; I have done it many times. And yes, I can tell the function of each part, and even critique the design. And make suggestions for change.

Electronics has been my hobby and vocation for 70 years or so. I am always learning something new.

Well, the multi section bar resistor had a bad section so I replaced that, bypassed the audio filter and The radio plays well. I showed my friend who owns it your posts and he is allowing me to leave the audio filter bypassed. He did this because of your reply and the other videokarma member's opinion. I have 2 more radios to work on for him so I will document the diagram with what I have done so a future generation will understand my work years from now. But I would like to say thanks for your assistance on this project. Thanks to everyone who assists on any posting I put up.