View Full Version : RCA Field Coil 15" + Baffle

10-24-2006, 12:03 AM
Well I hate this to be my first post, but I was told this might be a good place to find out information on a speaker I recently purchased. Original thread is here http://audiokarma.org/forums/showthread.php?p=859529#post859529

In any event what I picked up (for 75 bucks!) Is an RCA Theaterwide speaker. I don't know much about it, but I am going to attempt to restore it! If anyone has any information or knowledge on this piece, or even tips please don't hesitate to post. I am a novice at this kind of thing, and this seems to be a good project for me!



Steve Schell
10-25-2006, 01:54 PM
Minnesotastereo, welcome to Lansing Heritage! The history of the RCA theatre equipment is deeply intertwined with that of the Lansing and Altec products, so your questions about this system are very appropriate here. If you like I can bore you to tears with the historical details sometime.

Your system is an example of RCA's good stuff from the 1940s. It is from the era of RCA's second generation of field coil theatre apparatus.

RCA's first generation of Shearer Horn System inspired two way systems was introduced in 1936. The line included a number of multicellular mid/high frequency horns, W style bass bins and the 1400 series drivers. The 1428 and 1443 mid/high frequency drivers were the radical designs with center suspended phenolic cone diaphragms, and are the basis of the new field coil drivers that my partner and I have been building. The companion 15" field coil woofer was the famed MI-1444.

In 1940 RCA introduced the 9000 series drivers, which were used at first in the smaller systems such as this one. They featured fully enclosed cast pot motor structures and other economizing measures. The 1400 series drivers were discontinued in about 1942 due to high production cost and the 9000 series drivers were then used in all systems. Sometime in the late 1940s the permanent magnet 9000 series drivers were introduced and the field coil models were dropped; there was probably some overlap between these events. This MI-9444 is the second generation field coil woofer, not quite as collectible as the 1444 but still a potent and excellent woofer. The sound of this one in the small W bin should be very clean, punchy and pleasing, though with little output below 40Hz. or so due to the enclosure design.

This system was probably used with one of the later generation RCA fiberboard and metal construction 300Hz. multicellular horns or one of the wooden flat front divided throat horns (they look like W.E. 24A) mounted on top. This system probably used the MI-9443 field coil mid/high frequency compression driver, which like the earlier 1400 series shared the same basic motor structure with the woofer. The 9443 was of conventional compression driver design (sigh), with phenolic dome diaphragm and through-the-body exit. All subsequent RCA theatre compression drivers through the 1970s were basically similar, though differing in magnet and phasing plug evolutions.

If memory serves the MI-9476 dividing network is a 300Hz., 12dB/octave 2500 ohm device. The impedances were transformed to the individual drivers with tapped autoformers. I have seen a number of these networks sell for quite a bit on ebay and I wondered if the buyers realized that they are designed to operate at 2500 ohms. The old power amps in the projection booth had a 2500 ohm tap on the output transformer, which allowed for minimal losses in the loooong cable out to the speaker location.

You should be able to get these components up and running easily. If an MI-9443 compression driver cannot be found (they are scarce) then one of the later permanent magnet drivers will serve well. One of the appropriate horns for the system can probably be found for not too much money as they surface regularly. Then you will have a super good, toe tapping mono system for enjoying Ella and Duke.

Don't try feeding an audio signal to the woofer until you supply the 115VDC to the field coil. A field coil driver has almost no gap flux until the field is energized, and any signal applied to the voice coil results in heat rather than sound. The voice coil can be easily burned out this way; don't ask me how I know. These woofers have a 30 ohm voice coil, which is wound with a jillion turns of very fine wire, so they are more delicate in this aspect than most. Properly energized the 9444 is a high output, reliable device.

10-26-2006, 12:46 PM
Wow... you really know "stuff"! thanks for the input. That is very helpful. Later on when I begin restoring it I will use this as reference. Thanks again!

Steve Schell
11-01-2006, 12:08 PM
It looks like minnesotastereo opted for a quick flip and potential parting out instead of a restoration project. Here's the auction... sigh...


scott fitlin
11-01-2006, 12:31 PM
Yep, sadly, that IS what they come here for. To find out the real value of what they have!

However, he gets his cash, and hopefully, someone that buys them, restores them, and has audio history to enjoy.

Even though we get used for our knowledge, so they can sell for big bucks, its still better than the stuff being thrown in the trash!


11-01-2006, 03:57 PM
Another one bites the dust. It almost doesn't even hurt anymore. Minne did say he didn't really want 'em in the 1st place. Said 'thanks' too.

Which I'll do as well, Thanks Steve, I'm a closet RCA fan, something about the dog eyeing the speaker I think. Your story placed some missing pieces...no...was just flat enlightening. Don't think it wasted.:applaud:

Objectively, we had 'first' crack at them.....if anyone had to have them they could have PM'd a VISA # right away, maybe they did. Hell, I've no room, and I'd have doubled his money...:banghead:

And we got some good pix in return, even the story to go with them, all in one place. :)

RCA....Steve, to me, the 15" here looks a lot like a Jensen, especially the cone/cap, and the other hardware does too, but I've never seen any licensing tags on Jensens saying so. Was there ever any 'subcontracting' going on with those two? (Yeah, Jensen's in the other closet).

Or, if you'd rather, I can start a new thread with some pix and Qs on what I got for $75...........;)

Steve Schell
11-01-2006, 04:48 PM
Hi Scott, moldyoldy,

I guess what disappoints me about some of these visitors is their often mercenary attitude toward the rare equipment they happen onto, and the disingenuous way they seek to gather enough info about it to maximize the high bid. Rereading minnesotastereo's posts, he twice stated his intentions to restore the system. I don't mean to dump on anyone with an inquiry, just the ones that are not up front with their intentions. I do enjoy sharing the historical info I have been able to gather.

Scott, you point out correctly that this gear will wind up in appreciative hands. Since most of this stuff is already in the ground, this is a good result.

Moldyoldy, that does look like the same cone and dustcap (or very similar) as was used in the Jensen F15-LL and P15-LL. Hawley Products made most of the cones used by the major U.S. manufacturers in the old days, and the same cone can sometimes be found in different brands. The stamped steel basket of the RCA MI-9444 woofer was also used in the permanent magnet MI-9449 series woofers that were built into the 1970s. It bears a strong resemblence to the Cinaudagraph 15" baskets of the late 1930s through the 1940s, and this may be more than coincidence. I have collected a few RCA drivers, mostly late '30s vintage, that were built with Cinaudagraph parts and may have been OEMed for RCA by them. Trying to figure out who made what for whom is part of the fun of studying the old stuff.

scott fitlin
11-01-2006, 05:45 PM
I don't mean to dump on anyone with an inquiry, just the ones that are not up front with their intentions. I do enjoy sharing the historical info I have been able to gather.

Scott, you point out correctly that this gear will wind up in appreciative hands. Since most of this stuff is already in the ground, this is a good result.

Exactly my feelings. If someone comes here to find out about what it is they got, and what kind of value it has, I dont mind sharing info with them. I think its OK to tell people what they have and what it might be worth. I just wish they would say so upfront. There is no need to masquerade as an audio lover, if you have something you got your hands on, and want to sell it, no problem with me. Heck, every once in a while, it might even be something someone here wants very much! Just say what your intentions are, and thats that!

And, someone getting the gear, that really wants it, and will keep it, well, that keeps it alive. Somebody will get to enjoy it, and that is the whole purpose, as well as the buisiness of making money!

Truthfully, if it werent for the buisiness of selling, and things like ebay, much vintage gear would have been trashed! So, its really the motivation of making money that keeps some things out of the garbage dumps to be available to buy, by people like us!

The only downside to all of this, is the ever increasing prices for vintage audio items!

And of course, there is something to be said for this site, and this particular site, being known as the definitive place to come for audio info on many great American audio treasures. Many great minds in this one house! I get a nice feeling after I tell someone what to get, how to set it up, and they come back after a period of time saying " OMG, I never knew anything could sound so good "! In some ways, its like we are running our own subculture here, and WE are the bosses!

Jus my point of veiw!


11-05-2006, 03:37 PM
This brought $1300+, pretty good flip from $75. Hope there's a site contribution......


11-09-2006, 03:32 AM
It looks like minnesotastereo opted for a quick flip and potential parting out instead of a restoration project. Here's the auction... sigh...

yes i think he does it for a living. http://www.minnesotastereo.com/ i believe he was banned over at audio karma for lying about not having a store of any kind. its sad, be honest its not that hard to do. REGARDS JIM

08-06-2007, 08:05 AM
Hello everyone. I know it's been a while since I posted but I found this site again when checking on someones paragons on eBay. I know it probably won't mean much to anyone, but I'd like to sincerely apologize. It was not right of me to come on to this forum and have my first post be a "whats it worth kind of deal."
To be honest, I truly did want to restore them. However, some bills came in that I had to deal with (tuition for one), and I realized it was just too major of a project to handle on my own; especially considering my lack of knowledge and skill on these type of pieces.

I'd like to address my AudioKarma ban brought up by JIM. I do not own a store. I do not run a store. Like many people on this forum and theirs, I frequently buy vintage gear, flipping some and keeping some. It's a hobby. If you ever have checked my auctions when I had items for sale, you'd notice I don't use reserves, I start everything at a penny, and don't use buy it now.

Anyways... like I said before, I'm sure this won't mean much but I am sorry about my approach on this forum.
Best of luck to you all

Steve Schell
08-07-2007, 11:09 AM
Apology and explanation duly noted minnesotastereo, and you are welcome back here anytime. Please let us know about any more rare stuff you come across.