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Old 3rd Apr 2019, 6:43 pm   #1
don200002
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Default GEC (Gecophone) BC761 choke required

Hi all
I have restored this radio and use it on a daily basis. The original fault was an open circuit anode choke BC761. The set is working with an old smoothing choke that I happened to find among my box of things that might come in handy sometime. It would originally have required a high impedance speaker but works quite happily with a Bush output transformer and low impedance speaker.
The problem is that the choke has a marked effect on the output frequency range, having tried several chokes with various results it would be nice to get an original. I think these chokes were also used in some Cossor sets from the same era(1930).
Any help would be appreciated and a high impedance speaker would be useful.
I've been looking for a speaker cabinet of the same period but I'm beginning to think it would be easier to make one as they are very expensive on the auction sites.
The model number is BC3140 and I think you will all agree it's worth trying to get it back to original spec.
Many thanks in advance, Don.
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Old 3rd Apr 2019, 7:26 pm   #2
Ed_Dinning
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Default Re: GEC (Gecophone) BC761 choke required

Hi Don, if the original choke is available it could be rewound.
I have also grafted a modern output transformer into a vintage case so that a modern speaker (in an old cabinet) could be used with a 20's set.

Nice looking set by the way.

Ed
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Old 3rd Apr 2019, 8:18 pm   #3
don200002
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Default Re: GEC (Gecophone) BC761 choke required

Hi Ed,
I have not removed the old choke I think the whole radio was built around it. That should be my next move as it could be a broken wire at the terminal end, unfortunately I can't get at it without dismantling most of the radio. Yes an output tx could be fitted in the speaker case. There is very little space inside the cabinet, not even enough to fit my choke so I'll have to bite the bullit at some stage. Thanks for your input, Don.
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Old 3rd Apr 2019, 8:34 pm   #4
Cobaltblue
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Default Re: GEC (Gecophone) BC761 choke required

I don't think Cossor chokes are that similar I have a BC3140 and an awful lot of Cossor sets.

They are bit of a pig to work on.

As was the fashion of the day the only thing easy to change are the valves through cover and hatch on the back.

Cracking set.

Picture of mine attached

Cheers Mike T
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Old 10th Jun 2019, 1:47 pm   #5
don200002
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Default Re: GEC (Gecophone) BC761 choke required

At long last I have removed the choke and managed to get it out of it's case. The whole thing was set in pitch so not easy. However is is open circuit and I do need a replacement or a rewind. I forgot to mention before that the wooden valve access door was broken in half and while I was attempting to repair it my neighbour came across and said "don't bother repairing that I'll make you a new one" I have attached some pictures of the broken and remade door and when re-polished and fitted.
Over the last couple of months I have picked up an old PYE moving iron speaker which works very well with the set, and the luckiest find this year a BTH horn which also works fine, not exactly Hi-Fi but in keeping with the Gecophone.
Any help with the choke would be appreciated it's the final part of the puzzle.
Don.
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Old 10th Jun 2019, 3:12 pm   #6
don200002
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Default Re: GEC (Gecophone) BC761 choke required

Thanks Ed for your PM
More pictures attached
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Old 10th Jun 2019, 6:43 pm   #7
Ed_Dinning
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Default Re: GEC (Gecophone) BC761 choke required

Hi Don, that should rewind easily enough, but will need cheeks added. It can then be rewound with grade 2 wire without any interleaving paper.
It can be re-potted with paraffin wax, much less messy.

Ed
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