AM and Shortwave antennas - Videokarma.org TV - Video

trudie · #1 10-23-2015, 06:30 PM

I have a couple AM and SW radios from the 40's. These are small table top units. some of them are missing the back panel that would have the antenna attached to it. I know from my experience with tube amps a full recap and resistor check is in order. I am wondering on the lengths of wire and any instructions on replacing the antennas that would have been on the back panel?

zeno · #2 10-25-2015, 10:18 AM

The AM loop on the back may be part of the tuned circuit.
If so you will have to make one up.
To try it hook a 10 foot wire. Should get strong locals
& lots of noise. Same for SW. SW usually uses a diferent
screw. Dont bother with a really long wire, it will overload
the radio.

73 Zeno

trudie · #3 10-26-2015, 01:34 PM

73 Zeno When you say a really long wire will over load the radio, do you mean to use a shorter length of wire for SW, or to keep it at 10' as well?

zeno · #4 10-26-2015, 02:54 PM

Quote:

Originally Posted by trudie

73 Zeno When you say a really long wire will over load the radio, do you mean to use a shorter length of wire for SW, or to keep it at 10' as well?

Yup try 10'. Depending on the radio it may be able to
take a long wire for SW & maybe AM. If it overloads it just wont
work right & you get stations where they dont belong,
squeals & whistles etc. What brand is it ?

Zeno

Reece · #5 10-26-2015, 03:19 PM

However, as Zeno said, if the radio was designed with a loop antenna from the factory, and that rear cover mounted antenna is missing, the radio won't tune. You may get a mix of local stations all up and down the dial but they won't separate. If you list the make and model numbers of the radios here we can help.

trudie · #6 10-26-2015, 09:23 PM

Thanks guys this is great. Thanks for letting me know about the squeals and whistles, and maybe needing to experiment with antenna length. Before I try firing these up I'm planning a full recap and testing the resisters. The first one I am going to work on is a Midland M6b. Its AM only.
I also have a firestone Air Chief 4-a-22 that's AM and SW, A hallcrafters S-38 SW, a Zenith 5co2 AM, a karenola Trav-ler SW and AM, a Philco 37-600 AM, and a Philco 10552-A AM SW. I'm planning on tackling these one at a time after the Midland. Except for the Zenith I think they all are missing the back panel antenna. I'm thinking the Hallcrafters didn't come with one and its assumed you would have an actual antenna. If I can sub a wire for testing that would be great.

zeno · #7 10-27-2015, 10:26 AM

Interesting the Midland is the only set listed under "that" midland,
there are other Midlands. Its in folder #2.

Before you re-cap try to get the radio going first. That way you learn
& know its doable. May of the tubes are probably the same so you can
swap things around. When you recap do a few at a time then
test. Last thing is all these radios are probably "HOT" chassis.
Hooking things up wrong may expose you & others to AC voltage.
Get an isolation thansformer if you dont have one. An example:

http://www.ebay.com/itm/viz-isotap-w...0AAOSwAYtWJuBo

good luck
Zeno

trudie · #8 10-27-2015, 02:20 PM

I have a Veric, it looks like an isolation transformer is different. Does it some how prevent electrocution when touching the chasse?

trudie · #9 10-27-2015, 02:24 PM

After reading a WIKI on isolation transformers it sounds like something I should integrate into the VARIC box I am building?

zeno · #10 10-27-2015, 03:28 PM

Yes use them together. There are some nice combos but since
they are so useful they are expensive. Example:

http://www.ebay.com/itm/SENCORE-PR57...YAAOSwYHxWJCIl

If you have spare meters put one in for AC amps 0-5 &
one for output AC volts 0-150 Also fuse the output at 5A

73 Zeno

Quote:

Originally Posted by trudie

After reading a WIKI on isolation transformers it sounds like something I should integrate into the VARIC box I am building?

trudie · #11 10-27-2015, 04:14 PM

Zeno, you are spot on. I have a amp and volt meter i'm integrating into the veriac box. The veriac is open frame, and I found a open frame Isolation transformer that should work. Its rated 500VA at 115 vac. The veriac I scored is overkill, 10A. Should I hook the Isolation transformer in before or after the veriac? I'm thinking if I put it after the veriac I can do 2 outlets on the Veric box, one that's isolated 4A and the other that's not isolated if I need to check for faults before I buy a radio or amp.

Electronic M · #12 10-27-2015, 04:51 PM

Quote:

Originally Posted by trudie

After reading a WIKI on isolation transformers it sounds like something I should integrate into the VARIC box I am building?

You can do that or keep them as separate boxes that can be plugged into one another (easier to lug only one when both are not needed).

By the way it is spelled Variac and resistor not varic and resister. Technically a Variac is a trade name for a speciffic company's variable auto-transformer, but it has become like Kleenex or Bandaid...Synonymous with the product regardless of the maker.

zeno · #13 10-27-2015, 09:00 PM

Never noticed where but I would put the Variac after isolation.
With it you will be safe, can turn it down to break in a set &
sniff out weak tubes that wont run on reduced voltage.
Monitoring the current is essential for troubleshooting TV
Hoz & HV circuits in solid state ( SS ) sets.
Going higher is a good test of a SS sets regulator.
You can test things that run on 24 VAC or other low AC
voltages, just dont bump the knob !

73 Zeno

Reece · #14 11-04-2015, 05:29 PM

I would suggest going on NostalgiaAir and looking up the schematics for each of your radios. If the schematic shows a loop antenna that you don't have, put that radio aside for now as the radio will not operate without it. Work on the radios that still have their loop antennas, and on the radios that don't need them and will work on a length of wire. It would be frustrating to recap and spiff up a radio that needs a missing loop and not be able to have it work.

Later on, as you gain more experience, you can substitute or buy or make the missing loops.

Findm-Keepm · #15 11-04-2015, 06:22 PM

Quote:

Originally Posted by Reece

I would suggest going on NostalgiaAir and looking up the schematics for each of your radios. If the schematic shows a loop antenna that you don't have, put that radio aside for now as the radio will not operate without it. Work on the radios that still have their loop antennas, and on the radios that don't need them and will work on a length of wire. It would be frustrating to recap and spiff up a radio that needs a missing loop and not be able to have it work.

Later on, as you gain more experience, you can substitute or buy or make the missing loops.

I have a batch of loop antennas for sale over on ARF:

http://antiqueradios.com/forums/view...97803#p2397803

Scroll down a bit to see them all -