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Old 11th Dec 2018, 10:22 am   #1
Ian - G4JQT
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Default Ekco A22 circuit changes

A question for the Ekco experts!

I'm restoring an A22 and have noticed a few circuit differences between real sets and the circuit. S/N 017772

There's a 1nF capacitor fitted across the input side of the LW antenna coil on my A22 which is not on either the Trader sheet 768 or Ekco service data.

The V2 anode coupling capacitor is given 50pF on Trader and Ekco sheets, but mine is marked and measures 15pF.

V2 suppressor grid is shown on Trader and Ekco sheets connected to V2 cathode (and its biassing arrangement), but mine is connected directly to the chassis.

Not sure if these are likely to be deliberate production changes or errors.

Can anyone throw any light on this?

Thanks.

Ian
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Old 16th Dec 2018, 11:25 am   #2
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Default Re: Ekco A22 circuit changes

Incidentally, the second IF can has one coil and capacitor as per the circuit, but the other a smaller coil and a larger capacitor - 220pF rather than 100pF.

A circuit improvement, or running out of parts towards the end of the run, but makes no noticeable difference?
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Old 16th Dec 2018, 8:59 pm   #3
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Default Re: Ekco A22 circuit changes

This has been noticed before on A22 restorations see post #19 which is talking about the same capacitor.
https://www.vintage-radio.net/forum/...d.php?t=110919
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Old 18th Dec 2018, 10:16 am   #4
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Default Re: Ekco A22 circuit changes

Thanks Stephen. I missed that. Yes, it's obviously not a bodge. Either they tweaked things to account for parts supply or tweaked things for performance improvements. Who knows now...?

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Old 13th Mar 2019, 10:49 am   #5
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Default Re: Ekco A22 circuit changes

Compared to the published circuit, this change appears to give a wider IF bandwidth with a gentle double hump.

With a wobbulator on both this became obvious.

Ian
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