RCA 106 Radiola Speaker on eBay

CRL sent me a 'heads-up' on the sale of a vintage RCA 106 Radiola loudspeaker on eBay (But It Now: $375.00). The tapestry seems to be in excellent condition, as does the cabinet.

http://www.ebay.com/itm/1920s-ANTIQUE-RCA-106-COIL-TAPESTRY-SPEAKER-THEREMIN-RADIOLA-VERY-CLEAN-/221378398891

I have one of these babies and I know it sounds great in an RCA but I have no idea how it would be with a modern instrument. One of the disadvantages of it is that it emits a low hum. This is not noticeable when you are playing, but can be clearly heard when the instrument is silent.

In fact, I posted a video a couple of days ago where I used an RCA (Dr. Hoffman's instrument) with a Radiola 106 which I bought on eBay last fall. It is featured in the second half of the following:

http://www.youtube.com/watch?v=UzbRl0f3FMI

I do not know about the guy singing but that Hoffman standing stoically beside him moved me. The Hoffman represents the Class that has been lost in today’s want to be classic theremin. The time is nearing when it will return.

I hope no one thinks they are going to plug into this 106 and get the classic sound, the speaker is only a small part of it. The hum most likely comes from the fact that speakers in the old days relied upon being part of the power supply filtering and so it needs a high dc voltage on the magnetic coil to operate.

Just my thoughts…

Christopher,

When I purchased my RCA 106 Radiola on eBay last fall, I corresponded with vintage theremin connoisseur & expert, Andy Baron, who made the following remark in one of our email exchanges:

"...There will be some light background hum -- there always was on these, unless you're Reid, who added silicon diodes and iron chokes to get a 106 quieter.  As they are, they're generally quite all right, especially as soon as you start playing -- the background noise level becomes all but unnoticeable."

What do you suppose Reid did with silicone diodes and iron chokes? Unfortunately, Reid is not available to ask, and the guy with the harp in the video doesn't know his arse from his loop antenna!

Price for speaker dropped to $250 buy it now!  Link  Sold

Only read this if performance out weighs purist.

After a little digging I may have a solution for the tapestry speaker in question and the Hoffman hum issue. As a garage hacker it gives me leeway to try things. This product below is so cheap I would buy one just to see if it would work. We need the direction from an engineer on the best way to apply it but it is straightforward to me. Plug it into the wall or use the voltage available in the Hoffman cabinet.

• The first test is what is the actual voltage across the 106 RCA electrodynamic/field coil when it is in operation?  I have found it may be 87 vdc? What I am trying to do is eliminate the 60 Hz ripple on the magnetic coil.
• If the coil is part of the power supply to the rest of the circuits it should have a power resistor put in its place if it is taken out of the operating circuit. But I don't think it is, to tired to look at the schematic?
• Worse case scenario it will add a much higher frequency buzz (~16khz) to the sound but I don't think so?
• As a free standing tapestry speaker the voice coil impedance must also be considered, what ever it is.
• This HP resistor I believe would work with it for $1.13
• 4.3" x 3.64" dc regulator size.

Ebay located Quebec  Just down the street (-'

Actual Manufacture with Datasheet

djpb over at levnet could help us with this.

This is only a suggestion that needs exploration.

Christopher

I did not want to lose my research into this RCA 106 so I made a webpage to store the info.

More detailed photos are included. I would by it if I were in the area just to touch the past.

http://www.oldtemecula.com/theremin/rca106/

Christopher

I needed to update this thread because I refer to it on my WebPages and so does Google. I spent the last couple of days doing a parts search of whats available and thought through many possibilities of design which helps delay my encroaching dementia. I designed a dc power supply so the infamous buzz found in the RCA Radiola 106 speaker could be eliminated. I have heard there is another way to do it but my approach is robust, simple to apply, as well as cost effective. Only three people on the planet would find this subject interesting or know why it is important to retain the original 106 voice coil impedance match and the physical characteristics. If someone is not a purist they would miss the point and just swap out the old with a new speaker.

http://www.oldtemecula.com/theremin/rca106/

Christopher

Sometime in the 1940’s, Dr. Hoffman removed the 106 RCA speaker from his theremin and replaced it with a standard 10” GE. You can tell from the spacing of the hardware on the inside of the cabinet that the 106 had been the original speaker in the instrument. When the new GE was installed, new screw holes had to be made. The GE was attached with simple wood screws, but the 106 (which weighs far more than a modern speaker) had special receptacles for thick bolts designed to hold a much heavier unit. 

I think what happened was that Hoffman’s original 106 speaker was damaged in some sort of mishap, possibly in the studio. The speaker is dangerously placed, just a foot or so off the ground, with only the grill cloth to protect it. Here is a picture of the instrument in 1952 during the broadcast of the TV show TRUTH OR CONSEQUECES with host Ralph Edwards (in the zoot suit). Notice that Hoffman, by that time, had installed three vertical wooden strips over the grill cloth to protect the speaker. 

http://www.peterpringle.com/hoffpix/torc.jpg

As you know, I replaced the the GE speaker with a vintage 106 which was the unit RCA intended to be used with its theremins. It is my belief that Hoffman’s instrument was the second generation RCA prototype that never saw the light o’ day. When RCA stopped manufacturing theremins, Product Manager G. Dunbar Shewell, who had the prototype sitting in a corner of his office, gave it to popular N.Y. bandleader Jolly Coburn (with whom Shewell’s son, Lennington, played the theremin). We know from Hoffman himself (alias Hal Hope, who was also part of Coburn’s band) that it was Coburn who gave him the instrument to settle a debt. That was sometime around 1935. 

Since the 106 Radiola loudspeaker was used with a number of different RCA devices, it is far more common than the RCA theremin. They come up for auction on ebay from time to time, and should sell for between 2 and 3 hundred bucks, depending on the condition of the speaker, the cabinet, and the tapestry cloth. 

I am sure there are ways to reduce, or remove altogether, the hum associated with the 106 but it is essential that it be done without altering the speaker’s tone. If you change that, you might as well save yourself the trouble and expense, and use a modern speaker.