Driver from 1930 RCA radio, dead mag

lochness · 12th June 2008, 11:36 PM

I have a speaker from a 1930s RCA console radio. I think the magnet is dead as it won't work and a good sized chunk of iron has no attraction to it. I was wondering if you guys knew of a good place to send it out to be repaired (it doesn't need a new cone...thats the only thing in perfect condition).
I'm also trying to find a second one that is in good condition (meaning at least repairable condition). The Radio is a RCA Model 221 Super Heterodyne, serial number 24007-16. So if you know anyone who happens to have one and would be willing to part with it please have them contact me at: chishs@gmail.com

Yah but I need this one fixed first so I can test the impedance, thiele/small, and frequency res ponce.

I will post pics once I find a camera cuz you guys have to see it. They REALLY don't make em' like they used to.

Iain McNeill · 13th June 2008, 05:33 AM

Check to see if the speaker has a field winding as well as the voicecoil winding. They used to do that back then when magnets were expensive.

If there's a second pair of wires/terminals then you have to drive a DC current through the field core to generate the magnetic field for the voice coil to work against.

It's very hard to take all the magnetism out of a piece of iron.

lochness · 13th June 2008, 10:21 PM

Yah after talking to a speaker repair guy I read about how they used to make old speakers. I'm still going to have him do an overhaul on it to clean it up as I don't want to screw it up (now I know why there was a little transformer bolted to it).

If I can get a second one I'm going to modify on set of tube monoblocks I've made to work with them. I've wanted to make a pair of stereo speakers with a steampunk theme and this seems to be perfect for it (really like the screw in the middle of the dustcap(?).

I have to figure out how to transfer images from my mothers phone to the computer but my next post should have pics.

lochness · 26th June 2008, 12:46 PM

Ok this isn't my pic but they are from an auction for the exact one I have (I cant get the computer to download the pics from the phone).
Hopefully I win it...for a low price...I kinda wish modern speakers had screws right in the middle.

Iain McNeill · 26th June 2008, 05:26 PM

Ahh. they certainly don't make them like that anymore.

The cone was formed out a flat sheet so it has a seam. Some kind of phenolic spring stabilizing the cone at the center, screwed, as you say, to the frame. Tiny voicecoil.

I'd love to see the Theile-Small parameters for that baby.
Nice renovation project - keep us posted.

sreten · 26th June 2008, 06:04 PM

Quote:

Originally posted by Iain McNeill
Ahh. they certainly don't make them like that anymore.

Hi, Indeed ... they did not have any real bass in the thirties ...,

/sreten.

lochness · 27th June 2008, 12:41 AM

Quote:

Hi, Indeed ... they did not have any real bass in the thirties ..., /sreten.

And thus I decided I needed a dedicated sub-woofer for the project its going to be involved in. Funny thing...the RCA schematic, and info pages I could find for the radio it came from call it a "Fullrange" speaker and they used quotation marks.

Iain McNeill · 27th June 2008, 05:03 PM

compared to the victrola it was very "full range"

Pano · 27th June 2008, 07:12 PM

Sounds like a fun project!

Those RCA speakers will need a power supply, as you've figured out by now. The field coil that serves as the electromagnet was often used as the power supply choke in old radios.

Your RCA screw in the middle cones will likely sound best in some type of open back cabinet. Think old radio or even guitar amp.

I would suggest you go check out the Lampizator site
Endorphin and Nirvana pages for a good guide to using old radio speakers. Plenty of other fun stuff there too.

Keep us posted on the project.

lochness · 3rd July 2008, 09:12 PM

So I got the speaker back from the Speaker shop that I sent it to. Looks like a quality recone. They did add a spider and a dust cap. Now I'm wondering if the bolt in the middle of the cone is still there.

Hooked up the speaker to a makeshift powersupply made out of the transformer and rectifier from the 221 radio. Made a few small adjustments to an amp to drive it. Sounds good but different from anything I've ever used.

Should I risk removing the dust cap to see if the bolt's still behind it?

12th June 2008, 11:36 PM	#1
lochness diyAudio Member Join Date: Dec 2006	Driver from 1930 RCA radio, dead mag I have a speaker from a 1930s RCA console radio. I think the magnet is dead as it won't work and a good sized chunk of iron has no attraction to it. I was wondering if you guys knew of a good place to send it out to be repaired (it doesn't need a new cone...thats the only thing in perfect condition). I'm also trying to find a second one that is in good condition (meaning at least repairable condition). The Radio is a RCA Model 221 Super Heterodyne, serial number 24007-16. So if you know anyone who happens to have one and would be willing to part with it please have them contact me at: chishs@gmail.com Yah but I need this one fixed first so I can test the impedance, thiele/small, and frequency res ponce. I will post pics once I find a camera cuz you guys have to see it. They REALLY don't make em' like they used to.

27th June 2008, 07:12 PM	#9
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Sounds like a fun project! Those RCA speakers will need a power supply, as you've figured out by now. The field coil that serves as the electromagnet was often used as the power supply choke in old radios. Your RCA screw in the middle cones will likely sound best in some type of open back cabinet. Think old radio or even guitar amp. I would suggest you go check out the Lampizator site Endorphin and Nirvana pages for a good guide to using old radio speakers. Plenty of other fun stuff there too. Keep us posted on the project. __________________ Take the Speaker Voltage Test!

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13th June 2008, 05:33 AM	#2
Iain McNeill diyAudio Moderator Emeritus Join Date: Oct 2007 Location: Santa Cruz, California	Check to see if the speaker has a field winding as well as the voicecoil winding. They used to do that back then when magnets were expensive. If there's a second pair of wires/terminals then you have to drive a DC current through the field core to generate the magnetic field for the voice coil to work against. It's very hard to take all the magnetism out of a piece of iron.

13th June 2008, 10:21 PM	#3
lochness diyAudio Member Join Date: Dec 2006	Yah after talking to a speaker repair guy I read about how they used to make old speakers. I'm still going to have him do an overhaul on it to clean it up as I don't want to screw it up (now I know why there was a little transformer bolted to it). If I can get a second one I'm going to modify on set of tube monoblocks I've made to work with them. I've wanted to make a pair of stereo speakers with a steampunk theme and this seems to be perfect for it (really like the screw in the middle of the dustcap(?). I have to figure out how to transfer images from my mothers phone to the computer but my next post should have pics.

26th June 2008, 05:26 PM	#5
Iain McNeill diyAudio Moderator Emeritus Join Date: Oct 2007 Location: Santa Cruz, California	Ahh. they certainly don't make them like that anymore. The cone was formed out a flat sheet so it has a seam. Some kind of phenolic spring stabilizing the cone at the center, screwed, as you say, to the frame. Tiny voicecoil. I'd love to see the Theile-Small parameters for that baby. Nice renovation project - keep us posted.

27th June 2008, 05:03 PM	#8
Iain McNeill diyAudio Moderator Emeritus Join Date: Oct 2007 Location: Santa Cruz, California	compared to the victrola it was very "full range"

3rd July 2008, 09:12 PM	#10
lochness diyAudio Member Join Date: Dec 2006	So I got the speaker back from the Speaker shop that I sent it to. Looks like a quality recone. They did add a spider and a dust cap. Now I'm wondering if the bolt in the middle of the cone is still there. Hooked up the speaker to a makeshift powersupply made out of the transformer and rectifier from the 221 radio. Made a few small adjustments to an amp to drive it. Sounds good but different from anything I've ever used. Should I risk removing the dust cap to see if the bolt's still behind it?