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 Post subject: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Fri 09, 2012 2:00 pm 
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Hello Everyone,



I decided to write a technical and informative article on the 2ND All-Transistor "pocket" American-Made radio, that was developed and produced by General Electric in 1955. I noticed that there is a lot of information written on the 1954 Regency TR-1, but very little is written on the 1955 GE's First All-Transistor "pocket" radios....

The original invention and production of the World's first all-transistor "pocket" Regency TR-1 four-transistor radio, was announced on Oct 18th 1954 in the New York Times edition, and started to be produced by I.D.E.A. company's Regency Division. Raytheon had announced and produced the World's 2nd All-Transistor radio model 8TP, at the beginning of 1955, but it was a "large" portable eight-transistor radio. Raytheon had first made this announcement in the Wall Street Journal on Jan. 4th, 1955 and it went on sale to the public on March 1, 1955.

General Electric was the 2ND American-Made company to develop and produce an all-transistor "pocket" five-transistor radio, which it announced in the Wall Street Journal's August 24th, 1955 edition. General Electric also reported its "New" All-Transistor "pocket" radio development and production, in its September 1955 Monogram monthly employee magazine. This GE All-Transistor "pocket" radio was selling for a retail price of $49.95. And it measured: 5 5/8" length x 3 3/16" high x 1 1/2" deep, and it weighed 15 oz.


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Below is GE's 1955 official Press Release photo of its First All-Transistor "pocket" radio

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General Electric's First All-Transistor "pocket" radios were the models 675 and 676, which came in the colors of Black and Ivory. Below is an advertisement in December 1955, which shows the two model colors of Black and Ivory that were available for the 1955 Christmas season.


Note: The model 676 Ivory color All-Transistor "pocket" radio is sitting in the middle of top shelf behind Santa Claus.

Image


Interesting features ...

The 1955 GE models 675/676 circuitry consisted of (5) General Electric germanium transistors, which were the following: 2N136 (converter), 2N137 (1st I.F.), 2N135 (2nd I.F.), 2N78 (AF Detector), 2N44 (Output). All of these were PNP alloy-fused junction germanium transistors, except for the 2N78, which was a rate-grown NPN germanium transistor. All of these transistors and its electronic components were soldered onto a bottom printed circuit board. The top of the chassis has a "special" copper shield plate that is soldered to the tops of the Osc.+ I.F. tuning coil cans and is used to prevent "unwanted" radio frequency interference signals from entering this radio's circuitry.

The 2N136, 2N137, or the 2N135 Converter and I.F. transistors are located underneath the top copper shield plate. And if you have to replace any of these transistors, then GE had provided copper cut-out tabs over each of these transistors in the top copper shield plate. You would have to just bend up each copper cut-out tab, to gain access to the transistor needed to be replaced, instead of de-soldering and removing the entire top copper shield plate. The transistors 2N78 AF signal detector and 2N44 Audio Output transistors are not located under the top copper shield plate and are easily accessible on top of chassis, if you had to replace them.

The GE All-Transistor "pocket" radios had used 455 kHz for its I.F. frequency and its RF dial tuning range was from 540 kHz - 1620 kHz.


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Another interesting feature ...

The GE All-Transistor "pocket" radio's circuitry uses a DPST on/off volume control switch, that also uses a "special" 3-male pin battery connector, for a dual-voltage battery supply. The carbon-zinc DC battery used was an Eveready #239, that had (9) individual 1.5 volt batteries that were all stacked up in series. This battery also had a voltage tap at 4.5 volts and 9 volts, with a combined total of 13.5 volts. The battery has three female pin holes at the top that are labeled (-), (9v), and (13.5v). But, this battery can also supply another voltage, which is the tapped voltage of (4.5v), which you will get if you hookup the two top battery marked pins of (9v) and (13.5v). Other battery manufacturers also make this same "special" battery application, like the Rayovac 1900, Burgess XX9, and RCA VS304.

The GE models 675/676 All-Transistor radio used a (+) positive ground chassis and used the voltage tap of -4.5 volts and also the -13.5 volts, for its main battery line voltages.


Image


Another interesting feature ...

The reason why GE had decided to use two separate battery line voltage supplies in its original 1955 design, is that the -4.5 volts was used "only" for the 2N137 1st I.F. PNP transistor emitter "fixed" bias voltage supply and was also used for the radio's AGC (Automatic Gain Control) action. GE had used the -13.5 volts for the rest of the circuitry, including the "self" bias voltage supply from resistors (R12-2700 ohms + R5-2700 ohms + R4-220K ohms) for the base of the 2N137 1st I.F. PNP transistor. And when the radio's circuitry would receive a strong radio signal, the 2N44 audio output PNP transistor will conduct more current flow and thus there would be a greater voltage drop across the supply resistors for the base of the 2N137 1st I.F. PNP transistor. This will cause the base voltage to be less negative, while the separate -4.5 "fixed" bias voltage for the emitter of the 2N137 1st I.F. PNP transistor, will remain more constant. This AGC action will cause the "forward" bias of the base and emitter junctions of the 2N137 1st I.F. PNP transistor to be lowered and thus reducing the Beta (hFE) gain of this transistor, which will lower the overall radio's audio volume output.


Below is a schematic for the original 1955 GE Models 675/676 All-Transistor "pocket" radios ...

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1956 GE models 675-678 + circuit changes ...

In 1956, GE had added two more models and colors to its original All-Transistor "pocket" radios. They were models 677 and 678, which were color Red and Turquoise. GE had also made some design circuit changes in all the radio sets (675-678) manufactured in 1956. GE had "added" a AF signal detector diode (1N87G) to its circuitry, which the 2N78 NPN transistor was previously used to perform this function. Now, the re-designed sets would give the full advantage and power of all of its Five transistors that were used in the circuitry, instead of one used solely for a AF signal detector. Also, in 1956 GE had eliminated (C13 - 8 uF) one of the two electrolytic capacitors, that was previously used in the radio's original 1955 circuitry.


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Below is a 1956 GE Factory Showroom photo, displaying all of its radios that it produced ...

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"Closeup View" of the photo above, showing all (4) GE All-Transistor "pocket" model 675-678 radios on middle shelf ...

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Another interesting feature
...

One interesting feature of the 1955-56 GE models 675-678 All-Transistor "pocket" radios, is that there is a resistor that is soldered to the back of the printed circuit board, which is easily visible and accessible. This radio did not use any negative regenerative signal feedback or "neutralization" circuits in its design, to prevent signal regeneration. Instead, GE would test each radio for "maximum" performance, by soldering a 100-470 ohm resistor (R7), that was used for the base voltage of the 2nd I.F. PNP 2N135 transistor. And if you had to replace any of the RF/IF transistors, then it would be necessary to check and change the R7 (100-470 ohms) transistor to get maximum performance out of the radio, without signal regeneration "squealing" occurring. The reason GE had used this method, is that its "early" transistor manufacturing production and its Beta gain (hFE) performance characteristics were not very consistent.


Image


Another interesting feature ...

And another interesting feature of the of the 1955-56 GE models 675-678 All-Transistor "pocket" radios, is that there is NO audio coupling electrolytic capacitor used in the circuitry. GE uses a pair of complimentary germanium transistors with direct transistor coupling. The 2N78 NPN AF Signal Detector transistor's collector is coupled directly thru the volume control to the 2N44 PNP Audio Output transistor's base.


Below is a 1956 advertisement, showing the GE model 677 All-Transistor "pocket" radio
...

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Below are a couple of options that were also available for this radio, at an extra cos
t ...

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Last edited by Rick Hirsh on Nov Sun 11, 2012 3:47 am, edited 1 time in total.

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sat 10, 2012 11:58 am 
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Very comprehensive write-up Rick!

You of course know that if a GE 675-8 set is turned sideways, what with it's grill style and brass tuning dial, it resembles a Regency TR-1...I'm sure that was just a coincidence... :wink:


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sat 10, 2012 12:41 pm 
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Thank you for that very interesting post. It is something I've been wondering about. I thought that perhaps the Zenith 500 was the second production transistor radio but it looks like GE beat them by a couple of months. It would interest me to see a list of all the manufacturers first models. I'll be keeping my eyes open for one of those 675 / 676's.

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sat 10, 2012 2:23 pm 
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Hi

Does any happen to have the schematics for the "later-designed" chassis circuitry, for the GE models 675-678 all-transistor pocket radios ? The later designed GE model 675-678 chassis design had "added" a 1N87G AF signal detector diode and also "eliminated" one of its main line battery bypass electrolytic capacitors (8uF).

If anyone has this later-designed schematic, could you scan and upload it to this thread ? I think that Sams Photofact has this one ?


Thanks and I hope that everyone is enjoying the info.

Rick


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sat 10, 2012 4:29 pm 
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The 675 is shown in Sams TSM-2. It tells of modifications to the original circuit with the addition of the detector diode and a resistor change. It does not mention the elimination of the 8 uf cap. That cap is across the -13.5 volt supply and is pretty small to make any difference in that application so I can see why they may have found that it could be eliminated without a problem. Here is the portion of the circuit showing the changes.

Attachment:
GE 675 Alt Sch.jpg
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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sat 10, 2012 8:04 pm 
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Rick Hirsh wrote:
Hi

Does any happen to have the schematics for the "later-designed" chassis circuitry, for the GE models 675-678 all-transistor pocket radios ? The later designed GE model 675-678 chassis design had "added" a 1N87G AF signal detector diode and also "eliminated" one of its main line battery bypass electrolytic capacitors (8uF).

If anyone has this later-designed schematic, could you scan and upload it to this thread ? I think that Sams Photofact has this one


The Sams (TSM-2 and Photofact 329-7) only shows that in some later models a diode was added (some versions used a 1N64, others a 1N87G according to the parts list). There are several other changes listed on the parts page, but again as Dave reported, there is no mention of removing the 8uF cap which is clearly shown in the schematic and parts list available here:

http://img685.imageshack.us/img685/882/3297intro.jpg

http://img846.imageshack.us/img846/4457 ... tslist.jpg

http://img542.imageshack.us/img542/214/ ... tboard.jpg

http://img577.imageshack.us/img577/9752 ... ematic.jpg
.


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sun 11, 2012 12:37 am 
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Thanks, Rick, for the very informative write-up on this historic radio & all the great pics---learned a lot !

John


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sun 11, 2012 3:37 am 
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Hi

I see that my original thread written is getting a lot of replies and I would like to personally reply back to them.


First of all, I would like to thank Richard (fifties) for uploading his GE model 678 and also the Regency TR1 radios. And you are correct that when the GE all-transistor pocket radios do look similar to the Regency TR-1's, when standing upward. I also have both of these radio models, and in my opinion, the GE models 675-678, have much better "Selectivity and Sensitivity" than the Regency TR-1's.

Secondly, I would like to thank John(xrhond91) and also RobertL, for their kind words. I try to not only write technical articles, but also include some "interesting" historical information as well, on the various electronic equipment that I am writing about.

Last, I would like to give a "special thanks" to Dave Doughty and also Jim(wiscojim), for uploading the Sams Photofact information and schematics. And both Jim Dave are correct that the Sams Photofact schematic of the GE models 675/676, does not list or show the late production changes, for the elimination of the original circuit's 8 uF electrolytic cap. But, I have noticed with Sams Photofact schematics, there is often missing or incorrect data information that is listed. For example, if you look at the Front cover page of the schematic that Jim was kind enough to upload, you will see that under "Power Supply", it says "4.5 volts DC & 13.5 volts DC in a pack form with common positive terminal". And if you look at the parts list under "Batteries", it shows (M1) -4.5v and -13.5v. But, if you look at the main schematic drawing, Sams Photofact shows the dual voltage battery (M1) and the main line battery voltages of -4.5v and -13v (should be -13.5v). This is often the problem that I find with Sams Photofact schematics. I will always try to find the original manufacturer's data materials and schematics, before I use any Sams Photofact materials.

Finally, I went thru all my research materials and found a "Late Production" schematic for the GE models 675-676. This "same" General Electric (Late Production) schematic is also listed on page 132 of the book titled "Pin Point Transistor Troubles in Twelve Minutes", by author Louis E. Garner Jr.(Louis Garner Jr. was also the contributing editor of the "Popular Electronics" magazine for over 25 years).


Here are "some" of the changes that were made by GE on its Late Production models 675-676...

1) Added AF Signal Detector diode to circuitry (1N87G)
2) Eliminated C-13 (8 uF electrolytic capacitor)
3) Changed R9 to 22k
4) 2N135 Transistors were used for X1(converter), X2(1st I.F.), X3(2nd I.F.)


Below is a "Late Production" GE schematic for models 675-676 .....

Image


Image



Thanks and I hope that everyone is enjoying all of the above info.


Last edited by Rick Hirsh on Nov Sun 11, 2012 12:26 pm, edited 1 time in total.

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sun 11, 2012 8:24 am 
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Rick Hirsh wrote:
in my opinion, the GE models 675-678, have much better "Selectivity and Sensitivity" than the Regency TR-1's.

Ahh, Rick old boy, you are conveniently forgetting that the GE's have five (5) Transistors, to the Regency TR-1's four (4). :wink:

Here's a scan of my five operating sets along with their re-stuffed power sources, and another one that you had sent me showing how to locate the date code;


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GE 675 batteries.jpg
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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sun 11, 2012 8:36 am 
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Just a bit of information. These sets were referenced in the GE transistor manual in a list of usable
transistors as replacements for other sets of the day. The manual is the 10th anniversary manual and
has 61 pages. I have a hi-def scan of the two pages list, if you want by pm.

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sun 11, 2012 2:16 pm 
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Hello Everyone,



"Thanks" again Richard(fifties), for uploading your photo of your "beautiful" 1955-56 sets of working GE models 675-678 All-Transistor "pocket" radios. The technical assistance and advice that I had given to you in 2005, seems to have worked well, for you have 5 out of 6 sets now working. That is truly remarkable, for these 1955-56 GE radio sets are probably the "most difficult" to understand and get working, of all the other early transistor radio models. In fact, when I had first e-mailed you in 2005, I did not know of anyone who had a "working" GE radio model 675-678 set, except for a guy named Aldo Andreani, who is a professor in Italy. I had also given him technical advice on these GE radio sets around the same time frame, and he was also able to get some of his GE radio sets working.

Also the photo that you have uploaded that I had e-mailed to you in 2005, shows a photo of the date code (540) that is stamped on the back of speaker coil magnet, which is the 40th week of 1955. The earliest date code that I have in my collection is (538), which is the 38th week of 1955. The other photo showing the (2) electrolytic capacitors is "flipped" or the chassis is turned the other way, from the photo that I have already shown previously in this thread of the (2) electrolytic capacitors, which is a 1955 "early production" model.

Last, you are "correct" with the fact that the GE model 675-678 are five transistor radio sets. But the truth of the matter, is that technically the "early production" 1955 models were really a four transistor chassis model with a AF signal detector diode in its circuitry, the same as the circuitry for the Regency TR1's. Transistors are actually back to back diodes. And GE had used the 2N78 transistor as AF signal detector diode, instead of a transistor amplifier. This was accomplished by using 2 of the 3 transistor electrode elements, which were the base and collector electrodes. The emitter and base electrode elements were electrically tied together in its circuitry, which there was "no forward" bias voltage between these two electrode elements and both having a -8.5v with no signal applied. GE's marketing was able to claim that its 1955 GE models 675-676 (early production) All-Transistors "pocket" radio sets had more transistors than the Regency TR1's, which were both selling for the same price of $49.95. And the consumer would think that for the same price, they are getting a radio set with "more" transistors in it or a more powerful radio set than the Regency TR1, for the same selling price of $49.95. The later production models 675-678, was truly a more powerful radio set that had five transistors in it. GE had added a separate AF signal detector diode (1N87G) in its circuitry and used the 2N78 as a transistor amplifier (Audio Driver) instead of just a AF signal detector diode. GE had also lowered the R9 transistor from 39K to 22K, to give the base and emitter electrode elements of the 2N78 (NPN) transistor a "Forward Bias" stand-by voltage (no signal applied), and cause the 2N78 to act as an amplifier transistor, instead of just a diode.

Finally, many "thanks" to also Steve (radiotechnician), for the GE manual transistor reference information. I also have this 10th year GE manual edition in my reference library. And this GE manual shows more information and changes, that GE had made to its "Late Production" GE models 675-678. GE had again made another change to its Late Production model 675-678, by changing the original 2N78 NPN Transistor to a 2N169 NPN Transistor.


I hope that everyone is enjoying all of the above info.


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Sun 11, 2012 10:33 pm 
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Rick, thanks for the techie explanations. There was quite a difference between how GE did things with their early radios, as compared to RCA; every time they so much as changed a resistor value, they would change the model's last number or letter.

Now regarding the difference between the early GE and Regency sets; there is always a trade-off.
As seen in the scan I posted (BTW, it was off the internet, not mine, even though I do have those sets in those colors), the GE is larger, it's a horizontal model, and can therefore sport a longer Ferrite antenna coil.

The Regency is smaller, a vertical set, and has a shorter Ferrite. With 4 Transistor sets, the length of the antenna Ferrite and it's coil mattered tremendously, and much more so than later 6+ Transistor radios required.

I have 8 operating TR-1's, along with my 5 operating 675-678's, and of course after this length of time, component aging certainly comes into play AFA performance. All have had their E-Caps replaced (the TR-1's under the PC board and out of site, with the originals left in place), and IF's peaked.

Comparing my best working Regency vs the same GE, I would give the GE the nod, but that's with 5 operating Transistors.

Richard

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Mon 12, 2012 2:59 am 
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Very informative post, thanks!
Here are a few pics of my 678 and 675.

http://www.flickr.com/photos/transistor ... 3550394830

http://www.flickr.com/photos/transistor ... 139501118/

http://www.flickr.com/photos/transistor ... 023149361/


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Mon 12, 2012 8:28 am 
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michaeljpro wrote:

Thx for the pix, and all credit goes to you for the Regency/GE comparison.

Do those sets work, BTW?

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Thu 15, 2012 1:20 am 
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Hello Everyone,


"Thanks" Michael (michaeljpro), for uploading your pictures of the Regency TR-1 and also your "beautiful" GE model 678. And my favorite color of all the GE models 675-678, is the model 678 "Turquoise" color. I also noticed that with the GE models 675 (Black) and 677 (Red), that the front gold lettering seems to wear off more frequently, than the other two models 676 (White) and 678 (Turquoise).



I have also found some "additional" information in my archives files .....

Below is a 1955 GE Advertisement in Spanish, which shows the "original" two GE models 675 and 676 All-Transistor "pocket" radios, that were available for sale to the public. And in 1956, GE had also "added" the models 677 and 678, that were also available for sale to the public.

Image


Finally, below are both the "Early Production"(Models 675-676) and also the "Late Production"(675-678) GE All-Transistor "pocket" radios. The "Late Production" models have the "added" AF signal detector diode (1N87G) added to the circuitry and is located just behind the volume control switch on top of chassis.

Image

Image

NOTE: The GE radio's 3-pin battery connector's voltage settings is different from the 3-pin locations that is on top of the dual-voltage battery supply, which is labeled: (-), (+9v), and (+13.5). And the reason for this, is the fact that the radio's circuitry uses a "reverse polarity" for the main battery supply voltage of 13.5v. And this GE radio's circuitry uses a "(+) positive" ground chassis, which means that the main supply line voltage will be -13.5v. Secondly, the radio's circuitry will also use the battery pins of (+9v) and (+13.5v) to gets the "tapped voltage" of (-4.5v), which is used for the other supply line voltage, and supplies the (X2)2N137 "Early Production or (X2)2N135 "Late Production" transistor's emitter DC voltage.

Image - RCA VS304 Dual-Voltage Battery top pin locations



Thanks and I hope that everyone is enjoying the above info.


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Thu 15, 2012 6:27 pm 
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I don't remember exactly when, probably in the late 50's-early 60's, but I worked in a radio/TV /small appliance repair shop and I remember working on small GE pocket radios that were a nuisance to repair. There was a metal plate across the top of the components and soldered to the IF cans. This made it very difficult to work on. And I wonder how many went back to customers without that shield?


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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Nov Fri 16, 2012 2:30 am 
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happy wrote:
I don't remember exactly when, probably in the late 50's-early 60's, but I worked in a radio/TV /small appliance repair shop and I remember working on small GE pocket radios that were a nuisance to repair. There was a metal plate across the top of the components and soldered to the IF cans. This made it very difficult to work on. And I wonder how many went back to customers without that shield?

I think it's a Copper plate, but to remove it entirely would have required unsoldering it from all the cans. I had to replace one can in one of mine, and simply had to unsolder only that one.

I found having to replace the trick volume pot/dual on/off switch with seven solder landings to be more of a PITA. I can see why these sets weren't really commercially viable to repair, given the time it would take, in many cases.

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Jun Sun 08, 2014 1:21 pm 
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Last week I found one of these radios at the local flea market. I had forgotten about this thread until I did Google search. Thank you again for posting this information. It appears my example is an early production model with a 548 date code. I see both the 8 and 20uf electrolytics, also I can see 1 2N137 transistor. If I'm reading the schematic correctly that was changed to a 2N135 in later production. I believe I'll leave mine in as found condition but I can appreciate the work involved in making one of these play again.
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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Jun Sun 08, 2014 4:51 pm 
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Very interesting thread, well done. I had to take a second look at a GE I picked up a couple weeks ago at a thrift store. It's a ca. 1960 P790A, but the family resemblance is unmistakeable. GE must have liked the basic design.

It's a six transistor, not currently working. I haven't done a thing to it yet.

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 Post subject: Re: GE's First All-Transistor "Pocket" Radios - 1955
PostPosted: Jun Sun 08, 2014 5:46 pm 
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Joined: Feb Fri 27, 2009 11:43 am
Posts: 1003
Location: Tucson Az
What family resemblance?
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Rob


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