General Electric X260

[Colin Boggis]

I've just bought one of these radios because it's so unusual. It's designed to run off a 2 volt lead acid cell or 125 v ac. What I find interesting is that regardless of whether it is on mains power or battery, the HT (B+) is always provided by a synchronous vibrator, which doesn't require a rectifier. I guess I'll have some fun replacing the transformer with one having a 240 volt primary, replacing the vibrator with a solid state Mosfet unit and adding a rectifier. For battery operation I guess it will be some NiCad cells and a regulator built into a pack to simulate the original accumulator. Another interesting and rather quaint feature was the floating green ball showing the state of battery charge - I think I can simulate that with a few LED's and a bar graph IC. All a bit pointless I know, but should be fun & keep the old grey cells working. Circuit of the vibrator HT (B+) supply attached.
Has anyone else worked on one of these? Anything I should watch out for?
I'll also need to make a frame aerial as it's missing. That should be fun too!

[henrymarpla]

The radio does not work at 125 v, that is only for charging the 2 volt battery, also this 2 volt voltage feeds the filaments.

[Herald1360]

It looks like the radio can still run from the 2V cell whilst on charge unless the CHARGE and ON switches are mutually exclusive in operation.

[henrymarpla]

But without the battery installed it would not work, it would burn the filaments.

[Herald1360]

Very true! In which case, hopefully those switches are mechanically interlocked.

[Colin Boggis]

Having now studied the circuitry I'm abandoning my original plans to try to simulate the battery & vibrator. Whilst it will no longer be original, as it will only be used on mains, I will scrap the original power supplies and fit a conventional HT/LT transformer/rectifier solution with regulators on both supplies. There's so much room for the parts and room for a bluetooth module too if the radio's performance warrants it. The construction is awful from a servicing angle - the coil pack is covering the bases of several valves, so I'm not yet sure how to tackle it. But at least it will keep my brain alert & working! I'll post some pictures in due course.

[G6Tanuki]

I was always fascinated by the idea of synchronous vibrators, which promised 'something for nothing' by self-rectifying the HT.

They never really caught on though - matching the resonance-characteristics of the transformer to the vibrator-frequency to get greatest power-efficiency while minimising contact-sparking was always a problem - by the mid-1930s Raytheon had introduced the 0Z4

http://www.r-type.org/exhib/aaq0314.htm

and synchronous vibrators faded away.

[Colin Boggis]

Whilst my first impressions were that servicing would be very difficult, it appears that I was wrong. The switch units that cover the valve bases can actually be easily "hinged" to one side allowing access. The charging transformer doesn't look too healthy, but the vibrator unit looks good, so I might resurrect it after all. Some more pictures of this monster radio are attached.

[unitelex]

If it were mine I would keep the synchronous vibrator as it is relatively rare and a unique feature of this set, part of its character. If you intend to run the radio for long periods or noise from the vibrator is a problem then how about a switched or plug in option to use a modern PSU while retaining the vibrator in situ for demo/originality when the modern PSU is switched-out?

Best Regards
Chris

[Colin Boggis]

I had had similar thoughts regards the rarity of the vibrator. I shall test it out to see if it works. Keeping it in place should be possible as the conventinal PSU will fit in the battery box.

[Colin Boggis]

After cleaning the contacts on the vibrator it works. With a 2v input the vibrator (when in the PSU unit) produces 140 V DC. As I will never use the radio on battery, I shall go ahead and fit a conventional PSU and not retain the old arrangement. Given the rarity of the vibrator there may well be people out there, most likely in the US, who would love to have it. I shall therefore seek to sell it on. I know that many enthusiasts will disapprove of my decision, but I prefer to make vintage items useable, not just keep them as show pieces.
Hence my regular addition of a Bluetooth module. I feel it's a credit to the original designers that their design can find a new lease of life - it's not just recycling, it's upcycling.

[vinrads]

I agree with fitting the power supply , any chance of a picture of the cabinet , Mick.

[Colin Boggis]

Hi Mick (Vinrads). Not at moment as it's in bits! You have to remove it all to gain access to the chassis. Side panels caught me out as they are held with small oblong push-on fasteners and I managed to snap off a fixing lug whilst removing them. I'll put a few pictures up once it's rebuilt. FYI - the case is in good condition for it's age as is the dial.

[Colin Boggis]

I've got this radio working now albeit poorly (waiting for a new 3Q5GT/G output valve). Thankfully the frame aerial for Medium wave is built into the lid and present, but the plug-in loop aerial that was originally supplied for use with the shortwave bands is missing. Does anyone have any details of this? Number of turns perhaps? Physical size can be estimated from pictures at Radiomuseum, but sadly no details are anywhere on the net, including various US sites. Here's hoping somebody can help, if not, then it'll be a case of another empirical design!

[Colin Boggis]

I was perhaps too hasty in writing my last message. I have found a good picture of the loop aerial from which I have ascertained the dimensions (approx 32 cm x 17.5 cm x 2cm) and it also looks from the picture that there are just 3 turns of wire within the frame. This will be a good starting point. I also found a Spanish language video about the radio on this link for anyone that's interested: https://www.youtube.com/watch?v=veqhWnQm2lg

[FStephenMasek]

Why not instead build a two volt power supply?

[Colin Boggis]

I've finally reassembled this monster. I call it a monster because it is very frustrating - it has to go together in a set sequence and I've spent ages assembling, dismantling and reassembling several times as I kept finding I couldn't fit bits after other bits had been fitted! It almost ended in the bin. I built a mains PSU using a shaver socket transformer with one of the 2 x 110V windings removed and rewound for 4 volts. The 110 v winding left for the HT had to either have some turns removed or be fed through a resistor - I opted for the latter as it was a simpler solution. I've resprayed the case in hammered copper, the nearest I could get to the original which was more rosy in colour - you can see this when viewing the inside of the lid which wasn't sprayed in order to preserve the GE logo. Boroadcast band is working fine after full realignment and capacitor replacements. Sadly I've given up on the 5 shortwave bands as I cannot get any data on the external loop aerial that is missing. I've experimented with various ideas but none have worked so maybe there's another issue not discovered. I did check the oscillator and it runs on all 5 bands. As I won't use the shortwave I'm not really bothered apart from not having found a solution. I'll move the radio on sometime and maybe a SW fan will take on the challenge. I've left the original vibrator PSU in situ, disconnected, and I've replaced the mains on/off switching with a microswitch as I don't like 240V AC on wafer switches. I also added a neon indicator on the dial backplate. Some pictures are attached of the radio as it is now.