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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 29th Oct 2017, 2:38 pm   #1
Brent44
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Default Eddystone 840C BFO

I acquired this one with virtually everything reworked/renewed, except that the BFO doesn't run. I have swapped valves to eliminate that possibility, the voltages are correct, the coil has continuity - I am stuck. Any suggestions would be welcome.

Richard
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Old 29th Oct 2017, 3:11 pm   #2
HamishBoxer
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Default Re: Eddystone 840C BFO

First things first, circuit diagram and check voltages around that stage. Eddystone users group have free downloads.
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Old 29th Oct 2017, 3:22 pm   #3
ukcol
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Default Re: Eddystone 840C BFO

Doesn't the OP's statement ..."voltages are correct..." indicate that he has already done that?
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Old 29th Oct 2017, 5:30 pm   #4
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Default Re: Eddystone 840C BFO

Sorry! I missed they had been checked.Too quick to answer and got it wrong.
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Old 29th Oct 2017, 6:24 pm   #5
Brent44
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Default Re: Eddystone 840C BFO

That's OK! Just to add some more info, the relevant resistors and caps are all in good condition,and as I said earlier, I have swapped valves to eliminate them for now. That just leaves the coil, its cap (which I assume is in the can) and the front panel control, which I have checked to confirm it is not shorting. I have also checked with my scope that it's not oscillating somewhere way off.

The previous owner has evidently gone through this as I can see he has also fairly neatly removed the coil, as I can see where he cut the connecting leads and has rejoined them. I suppose that is my next step, even to see if it will oscillate hung on a gash triode or FET!

Richard
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Old 29th Oct 2017, 7:46 pm   #6
ukcol
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Default Re: Eddystone 840C BFO

Given that the oscillator coil has been removed and refitted it is worth check that the wiring has been done correctly, particularly with regard to the phase of the feedback.
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Old 29th Oct 2017, 9:20 pm   #7
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Default Re: Eddystone 840C BFO

I hope it isn't my old one!
I didn't like the "U" series valves and dropper resistor stuff.
(hope I have the right set - I think so)
It got E series valves and Transformer input.
Did I do wrong? Still wonder...
It went at Stockwood Park some years ago.
At least it was safe - at least I reckon so.
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