RCA cabient from scratch and help needed on the next steps

Posted: 2/24/2007 11:31:27 PM
mikebuffington

From: AZ

Joined: 11/25/2005

Yeah, they're a press fit.

The wires are soldered to a ring that slides over the threaded part of the mount on the inside. They are then locked in place by the nuts.

Now, I have a question or two of my own to put out there. I've seen some photographs and drawings to guess that each base part takes 2 nuts, and the wire/ring is put in between them. Am I correct? I'm only guessing here, and don't have any more proof.

Also, I've been in touch with Ken and his RCA theremin mounting nuts are octagonal, and not hexagonal. I'm pretty sure they're original, but i've not seen or heard of octagonal nuts on the RCA other than this example.

According to Floyd (I had a fantastic conversation with him!), he recalled off the top of his head that the threading is 5/8" 18 tap (and the nuts are 7/8 diameter), and not the 11/16" 24 tap ( with 1" diameter nuts) listed in the McKeown/Sparks drawings. 24 tap is a nicer thread, but it's not standard at all by today's threading standards.

It seems like there can be lots of differences between RCA's.

My biggest concern is the distance apart of the 2 mountings for the volume loop. A Floyd replica that I have borrowed is about 5/64" less than the 2+15/32 distance in the McKeown/Sparks drawings. The set does not fit as nicely into my cabinet that has mounts exactly 2+15/32 apart. The antenna set that I made does fit my cabinet. I want to make sure that my replicas can fit a true RCA perfectly.
Posted: 2/25/2007 9:29:30 AM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

I have been reading Ether music and Espionage in which it is mentioned that there were two manufacturersof the RCA Theremin: Westinghouse and General Electric. Let's say that each company farmed out the cabinets and/or Antennae to some cabinet shop or manufacturer. At the very least there could be two slightly different versions of the RCA cabinet. I also read that many of the Theremins didn't work when the customer got them home, and none of the dealers knew how to adjust them. They didn't even know they worked much less be able to adjust them.

Food for thought.

ba
Posted: 2/25/2007 10:29:38 AM
Dayfan

Joined: 10/8/2005

RCA Theremins were made by Westinghouse and GE. The serial numbers starting with 100 were made by one and 200 by the other. Manufacturers often used parts they had on hand so variations in parts are common in electronics made back then. These things were made by people who made radios using the same parts as radios (except the large coils) by the thousands. The antenna fits in the socket as a slip fit, the slits allow a little give so the antenna can fit snugly into the hole. The slits are necessary so the snug fit will result in a good connection between the antennae and the socket. Attached is a photo of an original antenna socket and wire connection. The wire from the coil is connected to a large lug on the socket. Note the two hexagonal nuts. The lug goes between the nuts, i.e. one nut holds the socket in the case and the other nut holds the lug on the socket/nut. Photo at:
members.tde.com/mmckeown/thereminpics/AntNut.jpg

Mark
Posted: 2/25/2007 10:59:39 AM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

So is that to say that you agree with my assessment? Do you think it should be expected to find slight or, it seems you're saying, even large variations between Theremins?

Also, would you happen to know if there were two or more cabinet manufacturers of these Theremin cabinets?

ba
Posted: 2/25/2007 2:38:48 PM
Dayfan

Joined: 10/8/2005

Yes I agree. Slight variations between parts and values are common. An awful lot of electronic and mechanical parts are not really critical to how old equipment works. Resistors and capacitors commonly can be plus or minus 50 percent because of age or because different values were installed at the factory and the equipment will still work. I usually try the piece of equipment (radio I am restoring) and if it doesn't work and it is not a capacitor, I will change resistors to be within ten or 20 percent. The RCA Theremin cabinets that I have seen were all made by the Jamestown Mantel Company. The number stamped on the bottom edge of the doors is thought to be the cabinet serial number. I believe they made cabinets for GE and Westinghouse units.

Mark
Posted: 2/26/2007 6:14:43 PM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

Interesting. Were the two factories close to each other or did they have all the cabinets made in one place for some sort of uniformity?

As far as component values: I hear you! I'm just learning all of this stuff, but after I had a working circuit I would change values here and there and switch things around. It seems that little matters. Some of the biggest change in tone came from changing 27's in the oscillators. Fun stuff.

ba
Posted: 4/29/2007 9:53:14 PM
mikebuffington

From: AZ

Joined: 11/25/2005

[img]http://www.mikebuffington.net/photos/thereminworking/complete.jpg[/img]

Hi everyone! Yesterday was a very special day for me: My replica RCA theremin made noise for the first time. Take a look at my blog to see and hear Anastasia Termen make her first sounds and see all the work that went into making her work!

http://bedsidestory.livejournal.com/37706.html

I need a replacement tube, as mentioned in the blog and video. As soon as I get one, I'll post new info. Since it's not truly working yet, I haven't tuned nor serviced it yet. Any RCA owners or experts are welcome to visit my theremin and any help on tuning it would be appreciated.

Super extra special thanks goes out to Mark McKeown, Ken Brown, Bret Moreland, Ben Aldrich, Floyd Engles, Andy Baron, Jason Barile, Carlton Bradford, and anyone else who has helped out in any way! I couldn't have done this without any of you!

There's still so much work to do. Here's a short list: plate the antenna, finish the cabinet, make replica escutcheon, fix the winding issues, get better trimmer capacitors, replicate the tuner condensers, mill the pilot light socket...
Posted: 4/30/2007 11:14:13 AM
kkissinger

From: Kansas City, Mo.

Joined: 8/23/2005

To hear the first sounds from a DIY project is very exciting, indeed.

As you mentioned, the signal is weak. Will be curious to see what it takes for you to fix this. Perhaps the pitch variable oscillator is weakly hetrodyning with the volume oscillator or with an overtone of the pitch's fixed oscillator. Either that, or the output of the oscillators is weak.

OK, those are my guesses -- will be fun to hear what you do to get a better signal level.

Again, congratulations on a successful smoke test.
Posted: 4/30/2007 11:50:32 AM
mikebuffington

From: AZ

Joined: 11/25/2005

Thanks Kevin,

I'm hoping it's just the 171A that fails to glow/warm up/work. I only have 2. When the working one is in the oscillator slot, it makes the super faint signal. When it's in the amplifier slot, it makes the loud initial turn on pop.

I ordered a new tube. Waiting is the hardest part...
Posted: 5/3/2007 5:26:19 PM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

Hey Mike,

Good Job on your Theremin. It looks great: inside and out. Good luck waiting for those tubes!

ba

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