RCA Antennas?

I am seriously contemplating making a set of RCA style antennas for a theremin I have.

As you may know, with major help from Dayfan and others, earlier this year I made a set of drawings of the RCA cabinet and hardware.

While pricing material, I began to question some of the assumptions I made while doing the drawings for the antennas.

I have since found out that some of my assumptions may not be correct.

I've asked a couple of RCA owners to weight their antennas. I've recieved a response from two of them, but there is a small, but significant difference between the two. As most people know, a sample of two is not sufficient to draw any solid conclusions.

I'd like to ask anyone who may have an RCA theremin to weigh their antennas and forward the numbers to me. It is important that a scale accurate to at least an ounce (or even grams) be used since the heaviest antenna should be less than one pound.

I will be using the information to revise my drawings to provide the most accurate information to anyone who would want to make their own in the future.

You can send your measuremnets to me at

Thanks!

Jeff,

I want to build a set of antenna for my own RCA theremin project. I would love to have more info about this. I've talked to Andy about your drawings when you were working on them, and have sent a few emails to Floyd. I figure I can make the antenna myself (and hopefully inexpensively) as I have access to all the tools required. I haven't begun pricing brass yet though, and the fabricating expert I know is away for the summer.

I'm curious to know what would be causing the discrepancies in weight. What were your assumptions?

Also, I am looking to see if anyone would be willing to make molds of the switch and knob faceplates of the RCA. I would be willing to work with someone on this if anyone is willing to make a mold (silicon, alginate, etc... and a mother mold).

Yes, I'm curious about the discrepancies as well.

While doing the drawings, Dayfan gave me excellent information about their construction, but since we didn't actually have one to "dissect", I had to make an educated guess about the weight of tubing required.

I thought I was on the heavy side to make them strong and bending easy. I have come to find out they are actually about 50 percent heavier than that.

In addition, I've just been informed that the bases and tips are threaded and screwed in place. That would explain why the tubing might be heavier than expected.

After a bit more research, I've found that the best alloy, especially for the loop antenna, would be C260, also known as cartridge brass. I got this from brass instrument makers, who have a great deal of experience bending brass tubing.

Like I said, I will be revising my drawings soon to reflect these changes. Hopefully, I can get input from a couple more RCA owners (soon) before I do.

Your original drawings show a .25 inch tip on the bases and tips. Would threaded parts be longer? Are they still soldered to the tube (before plating or after plating)?

One question I raised to Andy was the thickness of the slits in the bases. He didn't see how they were so thin without the use of lasers, which obviously weren't around then. Without seeing one, I figured maybe they were cut with a jeweler's saw, and even wondered if they were 4 parts put together.

David Newton's antenna pic (http://www.thereminworld.com/pics/gallery/davidnewton/pitchantenna.jpg)
He counts 4 pieces total for the pitch antenna, but your drawings only show 3.
They really did do things the hard way back then...

I can't help with the antennae, but perhaps I can help with the question about getting some faceplaates molded. My girlfriend is a sculptor and I may be able to talk hher into making these products. (She is learning to resin mold and this may be good practiced for her.) Anyway, send me pics and dimensions and I will see what she says.

By the way, really nice cabinet you made there. I looked through your pics of the process and was very impressed. I also am a woodworker, thoug of that scale, I mostly build smallinh thigs at this time, slightly difficult to build large when one hasn't got a shop eh?

Samgar

When I did the drawings, I had only a general idea of how the antennas were constructed. The connection and tubing I chose are purely a guestimation. I'm hoping with this I will be able to bring the drawings much closer to reality.

If the pieces are indeed threaded, there's a good chance that they are locked in place with a bit of solder. One of my "helpers" actually put his genuine RCA antennas in a vice and tried to unscrew then with pliers! They did not budge.

Actually, their construction is a good example of efficient manufacturing techniques, keeping machining, labor, and waste to a minimum. I don't know that I'd call it "the hard way", but I would consider it a quality job.

I can't imagine either antenna being more than three pieces, although I'd be interested in other theories. It appears from the picture you posted that the internal connection may very well be threaded as it appears to be nearly the same diameter as the 3/8" end and approximately 1/2" long. You really wouldn't gain anything from making it longer. Is there any chance David Newton could chime in here and tell us what he knows?

The slits in the base of the antennas are made with a slit saw. I just checked the McMaster-Carr website and they have a wide range of blades (listed as slitting cutters) down to an astonishing 6 mils (0.006")!

Jeff S. etc.

I had an original RCA pitch antenna apart when I restored a RCA and made the sketch I sent you. The antenna base is not screwed together, it is soldered together. The slots in the base are made with a slitting saw, available from any industrial supply house. These are designed for making the narrow slots seen on the bases. The base and tip are solid brass and will add weight to the antenna. Seems you need a fairly accurate scale to deduce what size tubing to use. I don't think it would make any difference in operation anyway. I made a set of antennae from brass rod because it doesn't collapse when you bend it and they work fine on my replica RCA.

Mark

Jeff,

I can solve (maybe) the mystery. I can get an original pitch antenna and take it apart to measure the tubing wall thickness if you think it is worthwhile. I can get it in the middle of August. We need to keep in mind that manufacturers often used what they had on hand and not always the same materials for all units manufactured. It wouldn't surprise me if there are variations in how antennas were made. Screwing the tip in the end of a piece of tubing is a bit pointless if a push fit and soldering anyway. Just extra time and expense. The screwed in tips may not be original antennae.

Mark