GE P780 Restoration Page

This restoration project is for a piece of radio history. There had been several transistor radios produced in the 1950's, but they were very limited in reception capability. It was impossible to buy a portable radio that offered the same degree of performance as a home radio. Reception was limited, and sound quality was poor from the tiny boxes. GE, realizing that there might be a market for a high quality portable radio that offered the same performance as a home tabletop radio.

It is not a pocket transistor radio. It is a portable, but is heavy - 11 pounds. It has a five inch speaker, much better than the standard 2 1/4 inch speaker in transistor radios. It is a good DX model, with a true tuned RF stage and three IF filters. It is soundly built, intended to be able to take abuse without damage. Sensitivity and selectivity are very good - almost matching some of their later "Superadio" models. This radio lacks two things that became standard in later models - an internal AC adapater which would allow the radio to be used at home, and a headphone jack.

This is also a real creation of the time in which it was produced. It was the muscle car era - cars had lots of chrome, front grills, organic colors. This - is a muscle radio. Chrome edges, shiny grill - it looks like a radio a muscle car owner could relate to! Throw it in the back seat, take it to the track, listen to the game. Or throw it in the back of a woody with a surfboard, cruise to the beach for some surfing and have your music on the beach, even if you were miles from town. Some people might call it garish - others beautiful.

Internally, this radio uses full size components such as its tuning capacitor and IF coils, all of which look like they would be more at home in a tube radio of the time than a portable.

My example of this radio has been around a long time, and suffers a lot from age. So this article is concerned with restoration of the radio - which has a lot of dirt and signs of age. It works, but only gets a couple of strong local stations - so I have a lot of restoration to do. Because it is a piece of radio history, I will try to keep as much as possible original - I will not put in enhancements like ceramic filters and larger ferrite bar. Nor will I add an AC adapter or headphone jack. I won't attept to make it look brand new - it is a bit roached out, and I will leave just enough wear and tear to preserve its history.

This is the procedure I followed, it may or may not be the best procedure, but hopefully you can use it as a guide to do your own restoration work.

1. Remove the battery cover on the bottom of the radio and remove the batteries.
   

   An advanced feature of this radio is a strap that holds connects the battery cover to the radio. This can double as a battery pull. Mine came with the strap disconnected - it is obviously supposed to be attached to the radio with the screws attaching the battery compartment to the cabinet back.
   
   

2. Remove two screws holding the cabinet back to the chassis:
   

   One of the screws on my radio was stripped out - which may be a common failure mode. I am not sure if I want to do the metal work to fill the hole and re-tap.
   
   

3. Remove a screw holding a retaining clip holding the battery wires. Unsolder two wires from the battery compartment.
   
   
   
4. Remove three screws that attach battery compartment to cabinet. The battery compartment can be removed by tilting out of some plastic hooks inside the cabinet.
   
   
   
5. It is very likely that at some point, batteries have leaked inside the radio. If you need to remove the clips for cleaning, unsolder the wire that connects clamps on the battery compartment, then remove four screws:
   
   
   

   It is a very nice feature of this radio that batteries can all be inserted in the same direction - that is the purpose of the connecting wire. There was some sort of pad material behind the clips.

   
   
   

   I elected not to re-install the pads. They had deteriorated to being rock hard.
   
   

6. The handle literally crumbled in my hand. I have some leather work to do.
   
   
   
7. The handle clamps can be removed by bending tabs inside the cabinet.
   
   
   
8. This affords a view of the interior of the radio. I will show four views:
   
   
   
   
   
   
9. The antenna wire and tuning capacitor wire routing is critical. Other restorers have noted this, and I can confirm it. Take pictures similar to those below, and use them to guide you when you re-assemble:
   
   
   
   
10. If you attempt to power the radio at this point, note that in my radio, BLACK was positive and RED was negative!
    
    
    
11. Once you have photographed the wire routing, remove four screws holding the antenna bracket. I was most fortunate that the ferrite bar clips are intact - other restorers were no so lucky.
    
    
    
12. The antenna bracket can be swung backwards out of the way, affording a first look at the rear of the PC board and the complete dial string routing.
    
    
    
13. Remove a screw from each end of the board retaining bracket.
    
    
    
    
14. Unsolder a ground wire from the board retaining bracket. Note that the orange wire is routed through the gap next to the ground lug.
    
    
    
15. Remove three knobs from the front of the radio.
    
    
    
16. Remove two screws from the volume / tone switch bracket. One is obscured by wires.
    
    
    
17. At this point, unfortunately, you will need to remove the dial string. Don't worry, it is not that complex to re-string, and I've put the diagram below. The dial string in my radio was a brown color - time to replace! My first opportunity to use 80 pound fishing line - which tends to fray pretty badly on the end, so a bit of beeswax will help. Unstring the dial string, starting by flexing the spring in the idler pulley. Two cams can be removed by unscrewing with a nut driver. The dial string in this radio was old and brown enough that I replaced it with 80 pound woven fiber fishing line, which works perfectly as dial string. To make the knots on each end of the dial string, try the Surgeon's Loop.
    
    
    
18. Continue removing the dial string by loosing the adjustment on top of the dial pointer. The dial pointer slide can be removed with two screws on either side. The shaft assembly for tuning can be removed with two screws, and the remaining cam can be removed.
    
    
    

    For when you re-assemble the radio, here is the dial string diagram from the service manual:

    
    
    
19. Remove the dial display assembly by unscrewing 6 screws (two hidden in the view above). Once you remove the dial assembly, the light bulbs for dial illumination can be carefully slid out of their sockets.
    
    
    

    In my one and only nod to modern technology, I was prepared to change these lights to LED, because these bulbs are probably unobtainable. Fortunately for me, both of the bulbs still illuminate.

    
    
    
20. The radio dial can be removed from the housing by removing two screws.
    
    
    
21. The radio dial can be tilted off of the housing.
    
    
    

    Be extremely careful NOT to try to clean the back of the display with anything but a really soft cloth, lightly applied, to wipe off dust. The silkcreened lettering will come off with any chemical treatment.

22. The dial light illumination switch can be removed with one screw.
    
    
    

    It was necessary for me to disassemble the switch to clean the pushbutton. I took this close-up to show the screw that holds it together, and details of the construction. The fiber washer is under the contact teeth plate, to insulate the spring from the bracket.

    
    
    
23. Rotate the tuning capacitor cam to reveal three tuning capacitor mounting screws. Remove. If you have not yet removed the tuning cams, now is a good time to do so.
    
    
    
24. Remove two screws holding the audio output capacitor. The rear screw is hidden in this view, and doubles as a screw to retain the stairstep bracket. Remove the middle screw on the stairstep bracket which also retains a wiring clamp.
    
    
    
25. The circuit board slides up along two grooves in the chassis. The tuning capacitor can be lifted out of a slot.
    
    
    
26. Unsolder the wires from the speaker.
    
    
    
27. Remove four screws hold the speaker to the chassis. The rear two screws double to retain the dial lights.
    
    
    
28. Slide out three spacers from the rubber gaskets. If you are going to re-plate the chassis, you will need to remove the rubber grommets. After half a century, they will be very brittle and replacements very hard to find. So only remove if absolutely necessary, and be extremely careful not to tear them up.
    
    
    
29. The front grill is a separate piece from the chassis. It can separated by removing a number of nuts - some of which are hidden in this view.
    
    
    
30. The chassis is now isolated and can be cleaned or re-plated.
    
    
    
31. The grill is backed with a fiber panel that has the speaker grill cloth glued to it. I was informated by a local metal shop that the grill is a casting that would not survive a re-plating process. Some restorers have recommended vigorous brushing, which is what I did with Windows and dish soap. Be extremely careful - the grill is brittle. Because it is a sand casting, the finish is rough - so don't attempt to defeat this by making it smooth. Unfortunately, the sand cast process makes a lot of little pits which hold dirt and grime. Be patient and keep scrubbing.
    
    
    
32. The radio circuitry that remains is actually still functional at this point, but not aligned. Just clip leads for power and speaker. This is useful to troubleshoot problems - and I had one, an intermittent IF stage.
    
    
    

    Here is a top view of the PC board. This radio is a later version of the radio - advertised by the seller as a revision "F" - which seems to have more in common with the "H" than the "A".

    
    
    

    As another restprer noted, it looks like a museum of Germanium transistor types. I suspect more than one are breaking down and not fully functional, but in the interest of maintaining originality, I decided not to do the conversion to silicon - which would require re-baising and added components. If the radio quits working, I will have no choice.

    Somebody has already re-capped this radio, and I suspect it was long enough ago that the replacements are also going bad. Their soldering skill slightly damaged a pad, so I will need to be careful. This PC board is also an unusual type - single-sided but with plated through holes. I've seen this a couple of times before - these boards have all the disadvantages of single-sided AND double-sided. It makes soldering a bit more difficult.

    Here is a view of the back side of the PC board.

    

    The solder in this radio was a strange formulation of tin / lead and acts like more lead than normal, making PC board work difficult. Nevertheless, I was able to remove the first IF can, take it apart, and fix the intermittent.

    If you want to unsolder some of the wires to make servicing the PC board easier, here are some close-ups of wire routing. A slightly larger hole holds an antenna connection and a white wire. I put a dot on one antenna wire sleeve to identify it.

    
    
    

This completes the disasembly of the radio. This is my finished restoration - minus the leather work.

I'm not a fan of the graphic in either manual available on line, so I made my own "silkscreen" version. I think you can figure out the adjustment points on the tuning capacitor (hint - the smaller plates in the middle are oscillator!). I couldn't find an adjustment for the ferrite bar antenna - next time I am in there I may get brave and attack a suspicious looking piece of tape. This may not be a perfect indicator of component locations - my "F" revision varies slightly in board layout from both the "A" and the "H" manuals that are available online. But this is a best guess.

I've cleaned up the "H" schematic as much as I can from the manual, and split it into functional blocks. Again the "F" that I have appears to be slightly different, but the "H" version is closer than the "A". When I get time, I may do an "F" schematic of my radio, but reverse engineering a schematic is NOT an easy job! Sorry if these are a bit big.

Here are some links from other restorers and collectors. I am not responsible for the content or if they are broken.

Radiola Guy

Radio Jay Allen's page - different versions

Review

Another restoration page

Youtube demo

Yahoo group - almost inactive though

Sarah's Transistor Radio page

Nice photos of the radio

Interview with the designer of the P780