Reed Speaker in Unknown Transistor Radio

I have had the chassis of this small transistor radio for almost 30 years. The radio was given to me by a co-worker without the case. It is in operational condition.

The attached photos show the radio mounted in a plexi-glass enclosure which I adapted as a case. The radio sits horizontally now, but the ferrite antena shows that the radio must be turned, such that the ferrite antenna is horizontal for good reception.

The tuning knobs are not original, and I added external battery holders because the orignals were badly corroded, with one clip missing. The stained label in the battery holder mentions the possibility of using Mercury batteries.

I count 10 transistors, and some show the TI logo. At least one of the transistors is wired as a diode.

The 3V electrolytic supply bypass cap has "Japan" on it.

The variable tuning capacitor has "MITSUMIELECTRIC CO LTD".

Three of the 4 metal can pot core coils have embossed on top: "RCL PATENT no 542942 etal". This same marking is found in this unknown Japanese radio and in this Standard Radio from Japan.

The special feature of this radio is the reed speaker. I have never seen another reed speaker in a radio outside the first generation of radios in the 1920's. The sound quality is comparable to moving coil speakers of the same size. The high impedance center tapped winding of the reed speaker eliminates the need for an output transformer. The push-pull output transistors drive the three wires of the speaker coil directly. The paper label on the speaker reads "EIRE" and "2122-2".

It would be interesting to hear about other reed speakers after the 1920's, and if anyone knows more about this radio.

Regards,

-Joe

• Component side (152 KB)
• Angled view (141 KB)
• Top view (101 KB)
• Reed detail (46 KB)

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You've got an interesting piece there.  Looks like mid-60s vintage (those TI transistors have what look like 1965 code dates on them).  Those four IF and oscillator cans and the Mitsumi tuning capacitor are pretty common to a lot of different radios; nothing really special there.  However, this is the first time I've seen a speaker like that.  It was made in Ireland (Eire).  And something looks familiar about the part number on that driver transformer (partially obscured by a white or yellow wire looped over it)...looks like it could be either a Motorola or a Westinghouse part number...

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"It would be interesting to hear about other reed speakers after the 1920's"

Hi Joe.  Various models of the German DKE-38 and VE-301 use reed speakers, and they date  to the late 30's - early 40's.

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Todd, thanks for the inisght. It did not cross my mind to think of Ireland, for "Eire". What you called the output transformer that is visible at the center of the component side photo, is actually the back of the speaker, with two blue wires and one yellow wire comming out.

This design is clever that way, in that it does not need a separate output transformer.

So, if Eïre means Ireland, we have an Irish reed speaker. The partially obscured number says 2122-2.

Michelle, thanks for reminding me about the later use of reed speakers in low cost german radios up to the 1940's. The reason to use reed speakers has always been efficiency. For a given input power, reed speakers generally put out more audio volume. 100mW of output power could drive a reed speaker to full volume. Reed speakers were made with horns and with paper or even aluminum cones. The down side of reed speakers, is the tendency for sharper resonances and, therefor, lower frequency fidelity. Reed speakers also tend to exhibit higher distortion from inherent variations in the gap between the reed and the magnet, or worse, when the reed actually hits the magnet with loud bass notes.

Once 1Watt of Audio power became inexpensive to produce, in the case of American radios with the 6L6 power pentode, and it's myriad descendents, the moving coil speaker became the norm because of the much better fidelity and lower distortion.

---------------------------

On a related note about moving reeds versus moving coils, record player magnetic cartridges from the 1970's until the end of the LP era, also came in the equivalent of a moving reed and a moving coil.

The common magnetic cartridge type was the equivalent of the moving reed speaker. In this case, the needle moved the shank, as if it were a reed, which would vary the distance of a piece of ferrous metal to a permanent magnet. These variations in the magnetic flux, thus produced, were picked by a fixed coil in the magnetic flux path. (Right now I cannot remember if it was a small magnet that moved or simply a small piece of ferrous metal that moved in front the magnet, perhaps a member can elucidate this point)

The much less common, perhaps less than 10% as common, magnetic pickup cartridge was the moving coil type. The needle moved a coil in front of a permanent magnet, and the very minute signal from the coil was amplified with a very low noise preamp.

The interesting connection between speakers and magnetic cartridges is that the advantages and disadvantages of moving reeds vs moving coils were common to speakers and cartridges alike.

The moving reed/magnet cartridge produces much higher output, and is thus much more efficient at translating mechanical motion into electric output, but the ability to track the highest frequencies was more easily limited by the mass of the small piece of ferrous metal (or magnet) that acted like the reed moving in front of the magnet. Just as with the fixed coil of the reed speaker, the fixed coil of this cartridge could also be wound with many more turns than the moving coil type, and thus produce a large output.

The advantage of the moving coil cartridge is that the total mass that the needle had to move could be reduced. But the tiny moving coil is extremelly ineficient and produces very little output. To this day, it takes state-of-the art semiconductors to amplify the extremelly feeble signal of a moving coil to have a noise performance that is comparable to the very low noise that is easily obtained with a moving  magnet cartridge.

Thank you both for your inputs and I look forward to hearing more.

-Joe

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...The transformer I was referring to is actually below the speaker, next to the earphone jack and in the middle of a cluster of those TI transistors.  I'm venturing an educated guess that it is an interstage or driver transformer, coupling the audio signal into the output transistors.  There is a number on it that looks like 1?4A3048??? (the ?s indicate parts of the number that are not visible due to the crack in the plexiglas and the wire looped over the transformer).  In the mid-60s, Motorola and Westinghouse were still building electronics, as in radios and TVs, and used part numbers on their components that had a pattern similar to that one.  May give some insight into the actual manufacturer of that radio...

...Also, on the phono cartridges: you're referring to MM (moving magnet) and MC (moving coil) designs.  In the MM cartridge, it was actually a tiny magnet that was attached to the inner end of the stylus shank, that simply induced voltages in the fixed coils surrounding it as it moved.  In the MC cartridge, the shank moved coils inside fixed magnets, again inducing voltages in the coils as they moved.  The MC cartridges were considerably more expensive than the MM cartridges and, as you have noted, required extra equipment (transformers and preamps) to make them work properly, which further increased the cost of owning one. 

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Todd, the transformer number is 154A2048.

This transformer sits adjacent to the output transistors, which drive the three speaker wires, so it must be the audio driving transformer as  you suggest.

Thanks for the clarification on the MM cartridge. I remember the Moving Magnet name very well, however I also remember seeing diagrams that suggested the structure where the magnet was stationary, and the ferrous metal moved.

The moving magnet structure you describe is the common one. There is a very good diagram of the moving magnet cartridge Shure cartridge at

http://www.microphonesolutions.com/learningcenter.html

The moving magnet in the diagram at this link is soft-mounted at the base of the sytlus shank, such that the magnet mostly pivots, and the contribution of it's mass is minimized. Note the comparativelly large coils that give the moving magnet cartridge i'ts substantial output.

A cursory google search and some of my past measurements put the various voltage output levels for phono cartridges at:

Moving Coil: 150uVrms with 40 Ohm internal impedance.

Moving Magnet: 5mVrms into 47kOhms load

Stereo Ceramic: 100mVrms with >1Meg load

Mono Ceramic cartridge after 1960: 1Vrms with >1Meg load

pre-1960 Mono with Rochelle Crystal: 10Vrms with >1Meg load

Any of these values is likely to change by a factor of 2 between various models and manufacturers.

For magnetic cartridge output levels see a comparison at

http://www.sound-smith.com/denon/index.html

Regards,

-Joe

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On the subject of reed speakers, I have a GEC radio, BC3235, which is dated from early 30's and I believe is one of the first radios which contained a speaker in the cabinet. Up to this point it was separate horn speakers or headphones. However the reason I mention this is the radio has a reed speaker. Conventional paper cone then the magnet and coils on the back.

• Reed Speaker (166 KB)

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According to the well documented e-b auction nr. 360344631708,
the General Electric set P-807J must have a reed speaker, too.

Having a look to similar sets, uploaders should be careful by just guessing the speakers to be of  dynamic type.

Maybe the owner could have a look at the speaker, I'll write him a message.

Regards, Marc

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 Other variation:    

oldradio.tesla.hu/szetszedtem/340ge-zsebradio/regiseg.htm

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Thank you for adding examples to this thread. Sandor's page on his reed speaker is excellent! I used the Google-Chrome browser to read it in English. 

I just took a close look at my radio shown in the attachments of the first post above, and Sandor's radio, and they appear to be identical in layout. The speaker in Sandor's looks identical to the speaker shown above. It would be nice to see Sandor's model listed at RMORG.

Another example that is near and dear to me is one of the last tube radios to use a reed speaker: The Grundig Gloria 51GW in 1951/52.

This radio was the last in a series of simple regenerative detector radios that started in the 1930's as the DKE "Deutscher Klein Empfänger" and, like all of it's predecessors, it used very efficient and economical reed speakers.

The nickname "Heinzelmann" is sometimes associated with this type of radio. The connection is drawn from German folk traditions, and it emphasizes the fact that this radio could function with just one tube.

Regards,

-Joe

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Dear Joe!

Ok: :) My upload 2009.Unfortunately we forgot about it! 

www radiomuseum.org/r/general_el_p7411p_741.html 

Regards:

STS

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Dear Sandor:

Thanks for the reference. This example got me started on a search for other transistor radios with reed speakers. Looking through the RM database, I only found GE radios with reed speakers between 1959 and 1967. I found no other brands that used reed speakers in their transistor radios. Within GE, all reed speakers were about 2.5inches (6.5cm) in diameter.

The larger contemporary transistor radios from GE with 3inch or 4inch speakers were of the moving coil type. This makes good technical sense because very similar sound quality is obtained from a 2.5inch reed speaker or a 2.5inch moving coil speaker. At the 4inch size, the cone excursions become too large to sustain bass without distortion as the reed swings in the gap between the two permanent magnet pole pieces. A moving coil speaker easily outperforms a simple 2 pole reed speaker in the 4inch size range.

The following lists the 135 GE transistor models that I found in the RM database with reed speakers between 1959 and 1967:

I also own a General Electric experimenter's kit called "Project: Intercom Model no. EF-130" intercom kit from this era that used 2.5inch reed speakers.

It is still very surprsing that my random sampling of other early 1960's manufacturers in the RM database found no transistor radios with reed speakers, except for GE.

There are technical explanations in the German side of the forum for various types of reed speakers. I read "Freischwinger" with the google translator. There is also a very fine treatment of the speaker topic in Ernst Herb's "Lautsprechersysteme". This link is in pdf form, which is more difficult to use with the google translator.

Best regards,

-Joe

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Dear Joe!

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> At the 4inch size, the cone excursions become too large to sustain bass without distortion as the reed swings in the gap

There's no particular upper limit on reed motors. I recall a ten-inch cone from the 1930s which played well.

I believe reed motors need careful manual adjustment.

Some types of reed speakers can be tuned to negative mechanical resistance. In principle this could negate some portion of electrical resistance loss; it could also self-oscillate or just flop over to one side and be stuck.

Voice coils need precision machinery but no adjustment.

With large production runs, VC may be cheaper.

On the same machinery, a variety of voice coil motors can be produced to suit different needs. Reed construction may not be so flexible.

A reed speaker may be designed for higher efficiency over a narrow range. Outside the field of consumer radio, reeds may have remained in production for special applications such as "sound powered" (no battery) intercoms. If the machinery is functional but demand is low, it may make sense to re-introduce reed-speakers when it may lower the cost of a radio. It would appear that GE had old reed-making tooling with ample capacity.

Moving armature drivers are still the standard driver in hearing aids. They have also been de-tuned and up-priced as very loud iPod earbuds and as in-ear monitors for on-stage musicians.

Voice coils might offer longer excursion, but a one-way (no woofer/tweeter) speaker can not use large excursion without annoying intermodulation.

The book Electroacoustics by Frederick V. Hunt, 1954, has historical context on a mind-blowing number of speaker inventions, and then good analysis of the several main mechanisms, including Moving Armature. ABE.com has the 1954 edition at $90 and what appears to be a 1982 ASA reprint for $40.

> "Lautsprechersysteme". This link is in pdf form, which is more difficult to use with the google translator.

PDF files have permissions. This one is tagged "Content copying: not alowed". So while it has machine-extractable text, an honest PDF reader will decline to copy it for futher use.

If you go to Google, More, Translate, and put this file's URL in the box, you get a link to a translation which appears to be in English. However copy/paste gets you mixed German and English. Hovering over a word gives you the original; copy gives both.

"For better sound you get by not Membrane den magnetisch bewegten Teil bildet. Membrane forms part of the magnetically moved. Drei Systeme Three systems lösen einander ab, abgesehen von Seitenentwicklungen (zB follow each other, apart from side developments (eg das induktordynamische System, verstärkende Systeme usw.): induktordynamische the system, strengthening systems, etc.)..."

By clicking View Original I get German plain-text. I open a second Google translate window and put this text in the box, it shows the English, and this can be copy/pasted without German mingled in (except those words which Google does not know):

"For better sound you get by not to a better sound you get by not the membrane forms part of the magnetically moved. Membrane forms part of the magnetically moved. Three systems Three systems follow each other, apart from side developments (eg release from each other, apart from side developments (eg induktordynamische the system, Strengthening systems, etc.)..."

Because of differences in how the two languages are structured, the density of technical German and the high proportion of unknown words, and use of idiomatic forms, this "english" is Greek to me.

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Paul, it would be great to see more material on very small hearing aid speakers. If some of these are sufficiently antique, their data could be used to create new models. Perhaps some of the existing RM hearing aid models use the modern reed construction.

One great advantage of a sealed hearing aid is that the acoustic path remains at high pressure, which matches the high pressure and short excursion operation of reed construction.

Regards,

-Joe

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An internet search turned up a very good illustration and explanation of a modern hearing aid reed speaker.

This article describes a "conventional" hearing aid with a reed suspended between two poles which has essentially the same architecture as the speaker in the transistor radio above. The biggest difference is the very small high pressure diaphragm in the hearing aid, as compared to the large diaphragm in the transistor radio speaker that serves as impedance transformer to move a lot of air at low pressure.

The goal of the article was to demonstrate an alternative structure with balanced simultaneous opposing motion that imparts very little spurious vibration to the body of the speaker. This reduces spurious coupling from the speaker to the hearing aid microphone and reduces the possibility of feedback induced audio whistles.

Two animated ilustrations compare the conventional and balanced designs very clearly. Look for the subtle motion of the speaker body: There is some in the conventional design and none in the balanced design.

Regards,

-Joe

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The first reed speaker I ever encountered was in my parents GE P-800 which I remember well. It was not in the list of radios Joe Sousa (reply #12) compiled from the RM database. I just checked and the reed speaker is not visible in the photos in the RM record for the P-800.

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Hi Gary:

I see that you joined RadioMuseum recently. Welcome aboard, and thank you for the noting the P800 ommission.

I only found the P800A, and it's schematic confirmed the use of the reed speaker. I have updated the model description of the P800A to indicate the presence of the reed speaker. This correction should show up shortly, after it is reviewed by the model administrators.

If you are sure that your parent's radio was a P800, and not a P800A, you should enter a new model to the database by following the menus in the RadioMuseum homepage.

Best regards,

-Joe

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Hi Joe:
From my further research including a Sams Photofact I found (Folder 10 set 482), I conclude that there only was a P-800A, not a P-800 as I stated in my earlier posting. Thank you for catching this!

I'm attempting to locate a P-800A for my collection and it appears they are scarce. The one the family had was lost following one of many moves. I recall the volume control pot became quite scratchy with age. Otherwise it was a great little radio for the time.

Best regards,
Gary

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Hi Joe,

Thank you for providing such useful information of this type of speaker.

I have just acquired a GE P1710C which is one of the models you've listed as having this set-up and there is very low output from the speaker, due to the disintegration (to powder) of the two magnets in the reed assembly.

However, by using a hi impedance (2k Ohm) earpiece plugged into the earphone socket I can hear the radio loud & clear.

Obviously I need to find replacements for the two magnets and, on another vintage radio forum (here in the UK), a member has suggested using small neodymium type.

At the moment, I'm trying to find the right size magnets and should I be successful I will post an update on here.

Regards,

Tony

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Hi again Joe,

So that I can gather as much info on this assembly, in one of your photos in your original post, could you tell me if the circled items are intact magnets (as they seem to have the appearance of foam pieces) ?

I repeat your photo with the parts circled in red:

• Reed Assembly (28 KB)

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Also, does anyone know what material the magnets are made of that would cause them to crumble to dust/powder over time? Is it ferrite?

As an update, I have obtained a couple of bar magnets (19mm x 3.2mm x3.2mm) that are designed for use with glass tube encapsulated reed switches and I'll let you know what happens when fitted.

Regards,

Tony 

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Hi Tony:

Yes, the zones you circled in the "Reed Assembly" photo correspond to the two magnets.

The magnet material should be the then common AlNiCo alloy. It is a brittle and porous material. If the radio was played loudly enough for the reed to hit the magnets, then the magnets might have been fractured by impact and became more prone to corrosion. Was there other apparent corrosion in the metal parts of the radio? Was the radio stored in a humid place?

The bar magnets you got sound like a good fit, and I am going to guess that they are the conventional AlNiCo alloy type, not the Neodymium type.

Best regards,

-Joe

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It kinda has to be an Alnico. It takes more than that much soft iron to field a speaker. Ceramics were just getting invented. Rare-earth magnets are far in the future.

I have never seen Alnico turn to powder like that. But there are a LOT of "Alnico"s. It isn't a "natural" alloy like lead-copper or iron-carbon. There are several alloys at different price/performance points. Some of the recipes can be cast or sintered.

Cast Alnico 5 is the standard for many "serious" uses.

Sintering is when you press a powder into shape and cook it almost to the melting point. Selection of grain shape and firing temperature can give a very dense part (lamp filaments, engine rods) or a very "loose" part. Modern sintered Alnico claims to be "mechanically strong"; I wonder if the cheaper sintered Alnico products withered when Ceramic came on the market much cheaper.

I'm wondering if this is some off-spec (for government work) material which was sintered so gently that decades of oxide intrusion opened it up.

The other thought is a very early primitive ceramic magnet. Modern ceramics chip easily. In hard-drives they "must" be painted so the crumbs don't crash the heads. But even when I've broken them, I've never seen the whole magnet turn to powder.

There is a maximum magnetic strength for a reed motor. Too strong, the reed just slams to the pole. As in any magnetic device, too weak is low output. However since there is no way to know the exact design, and a slam does no harm, just try what you have or can find.

You want to clear any mag-powder or glue debris from the pole piece where you put the new magnet. 

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As a further update, I've also obtained similar size magnets: 19mm x 3.0mm x 3.0mm that are used on model train motors. Perhaps these will be a diiferent 'strength' to the glass reed type I ordered earlier.

I'll keep the updates coming.

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Hi,

In short, one of the types of miniature bar magnets that I bought have been fitted and shazzam, the speaker burst into life.

However, there's more to the type of bar magnets used and their magnetic properties than the above simple annoucement reveals and my next message will contain fuller details and photos.

This GE P1710 does have a certain 'tone' and I'm not sure if that's how it sounded with it's originally fitted magnets and I have placed an audio clip on a website designed for off site audio storage but I don't know how to place a link to the site on here for you to be able to listen to the recording.

I'd be most grateful if someone could provide an idiots guide of how to put a link within a forum reply because, even though I read the advice given by R. Morg, I just don't understand how to get it to work.

Cheers

Tony

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In the 1960s both Sony and GE were making pocket transistor Radio Sets in "Shannon Free Zone" the then Duty Free  Industrial Estate at Shannon (not very old then) beside Shannon Airport and the "New Town" of Shannon. In the 1950s that area of Co. Clare, Ireland was salt marsh and bog beside Shannon Estuary. Originally Foynes on the other side of the Esturay closer to the sea was the Transatlantic stop for all seaplanes.

An extract reprinted in 2007 in "Limerick Leader" newspaper published originally in 1967

REDUNDANCY AT EI SHANNON WILL NOT BE SERIOUS

SOME 200 workers at the EI factory at Shannon Airport have, or are about to, become redundant. The reason is that initial orders placed for the start of 1967 are lower than anticipated. It is the first occasion since the factory-the largest-opened at Shannon that such redundancy has occurred and those affected are mostly married women employed on a part time basis and young male employees. The EI Company is the largest employer at the Shannon Industrial zone and manufactures electronic components which are used in radios, television receivers and record players. The firm's entire output is sold to the parent company in the Unites States General Electric Company. The President and Managing Director of the Company, Robert Page, in a statement stated that the smaller orders result from two major causes and that improvement is anticipated in the relatively near future. General Electric inventories of EI products are bigger than usual because consumer Christmas buying was much less than expected. "IF WE ARE TO SURVIVE WE MUST WORK HARDER"-MAYOR AN increase in the use of our resources must be done in partnership, a partnership between the employer who provides the capital and the management, and the employee who provides the necessary technical skill and it should be done because we are asked to do it for the sake of the country rather than because we are forced to do it by any Government law," Cllr Vincent Feeney, Mayor, stated when he opened the Irish National Productivity Committee "Joint Industrial Conference" in the Royal George Hotel on Monday afternoon. Over 40 delegates from various firms and industries throughout the city and county are participating in the four day Joint Industrial Conference. The Mayor, in the course of his address said that we in this country hated any form of compulsion and the easiest way to get any Irishman's back up was to tell him he must do something because the law says it. "There is in this area a great need for a school of technology," the Mayor continued, "where worker and management can train in modern techniques and there is a need too, which I will continue to refer, for a University so that we can encourage to come into this region persons of calibre and training required to retain them in the region."

My Emphasis in Bold.

The Shannon Free Zone is now just an ordinary Industrial Estate (no Duty Free) and the "EI Company" amazingly is still there, but as an indigenous company making CO and Smoke alarms.  I've no idea when Sony left. But their arrival is mentioned in the UK book "The Setmakers". The UK set makers were not amused by Irish policy at the time.

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