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Old 13th Feb 2019, 11:45 pm   #1
Glowing Bits!
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Default IF coil for GE radio.

Does anyone on this forum have a coil of the following spec? It does not have to be an exact match but the size is more of an issue than the resistance.
Both coils appear to be around 8ohms, the size is: 50mm high x 20mm square.
The set is an American AA5 clock radio.
Hopefully, someone may have one.
Rick.
P.S. the secondary is dead, in case anyone asks.
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Old 14th Feb 2019, 9:12 am   #2
Ed_Dinning
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Default Re: IF coil for GE radio.

Hi, a picture of the dead one would help and the value of the IF frequency.

Ed
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Old 14th Feb 2019, 6:37 pm   #3
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Default Re: IF coil for GE radio.

I have some IF cans from a scrapped Bush radio but they are larger than the size you are looking for. Do you know which one you need i.e. 1st, 2nd or 3rd IFT ? Is the secondary winding open ?
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Old 14th Feb 2019, 8:40 pm   #4
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Default Re: IF coil for GE radio.

The IF is 455KHz, here are some pics.
The dead coil is the secondary on the first can, between valve 1 & 2.
The core is adjustable for peaking.
Jolly, if the cans are higher, that will be fine but the width matters more, there are obstructions in the way.
Rick.
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Old 14th Feb 2019, 9:54 pm   #5
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Default Re: IF coil for GE radio.

Hi Rick

The IF coils are from a transistor radio, so I am not sure if these will be suitable for your valve set and also they have six pins instead of four. I am guessing that the first IFT coils are the ones immediately left of the gap where the oscillator coil was, which I have removed. Also I don't know the IF as I don't have the circuit diagram for it.

They measure approximately 15mm X 15mm x 25 mm. Picture attached.

If you would like to try them PM me, I will remove and send them to you FOC.

Cheers.
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Old 14th Feb 2019, 11:37 pm   #6
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Default Re: IF coil for GE radio.

It could be rewound if someone has a wave-winder on the go.

David
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Old 15th Feb 2019, 12:21 am   #7
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Default Re: IF coil for GE radio.

Most likely the secondary coil itself is ok, it doesn't look burnt. Probably one of its wire terminations has corroded through near where it was soldered. Or possibly the mica tuning capacitor has failed but less likely. In any case it looks repairable, probably, unless say there is greenspot corrosion in the winding where you cannot get at it. But it looks well protected with wax. Gently warm it up in the oven until the wax just melts, and try to get a look at where the winding wires are terminated.
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Old 15th Feb 2019, 12:52 am   #8
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Default Re: IF coil for GE radio.

Just a quick one, the coil by the base has been looked at under a good light source, it clearly has several bits of microscopically thin wire hanging downwards, it may possibly have suffered a blow-out but there's no sign of burning.
If the break was by the base, I would attempt a repair but the whole winding has several barely visible breaks, sadly.
Rick.
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Old 15th Feb 2019, 12:55 am   #9
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Default Re: IF coil for GE radio.

Jolly, thanks for the offer, I'll hold on for a bit longer to see if anyone comes up with a better solution before working out which way to go next.
Rick.
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Old 15th Feb 2019, 6:10 am   #10
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Default Re: IF coil for GE radio.

A bodge I have read about, but never tried, is to convert the circuit to RC coupling. Keep the primary (good) winding in-circuit, tuned to the IF frequency. Connect a resistor in place of the secondary winding to keep the bias voltage on the IF amplifier valve grid. Then connect a capacitor between the 'anode' end of the primary' and the 'grid' end of that new resistor to couple the signals.

No idea what values to use (off the top of my head, perhaps a 100k resistor and 100pF capacitor) but it might be worth a try.
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Old 15th Feb 2019, 12:56 pm   #11
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Default Re: IF coil for GE radio.

Rick,


I have a recovered IFT which is about the same size (19mm square x 47mm), which I've tested (see the thread in the homebrew section).


It looks similar yours, but the caps are polystyrene (should be more reliable than silvered mica), and the windings are about 11 ohms each (instead of 8 ohms). This shouldn't make any difference.

Yours for postage + PayPal fees (say, 1.20 in total).

dave
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Old 15th Feb 2019, 8:03 pm   #12
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Default Re: IF coil for GE radio.

Dave, I'll take your offer up.
Jolly, I might as well take your offer up while I'm at it, one way or another, the radio will be fixable, one hopes.
I have heard of the RC setup being used but never had a need to implement it.
Rick.
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Old 15th Feb 2019, 9:07 pm   #13
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Default Re: IF coil for GE radio.

Hi Rick
If you PM me your address I'll try to get the coils out to you next week. Thanks.
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Old 15th Feb 2019, 10:10 pm   #14
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Default Re: IF coil for GE radio.

PM sent.
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Old 16th Feb 2019, 10:40 pm   #15
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Default Re: IF coil for GE radio.

Rick,
You have a PM from me.
dave
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Old 18th Feb 2019, 4:56 pm   #16
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Default Re: IF coil for GE radio.

PM received and read.
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