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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 27th Jul 2015, 4:39 pm   #21
ms660
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Default Re: Murphy B40D L.O. / R.F. Alignment with scale

According to the book the front panel mounted osc trimmer capacitor shifts the frequency at 20 mhz by +- 5 khz from from the trimmers mid position, it's effect is less further down the band(s)

For anyone new to these receivers and fiddling about with the tuning drive etc it's important to note the the tuning capacitors shaft is ceramic based and as such should be regarded as delicate, when fiddling around with the stop bar adjustments etc the drive to the tuning gang shaft should be disconnected first to prevent possible damage then reconnected when all is well.

With mine I have a vague memory of setting the tuning gang not quite to full mesh once the stop had engaged just to be on the safe side, about 1mm off full mesh comes to mind, having said that I can't be absolutely sure as it was several years ago when I overhauled the tuning drive etc.

Lawrence.
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Old 27th Jul 2015, 5:14 pm   #22
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Default Re: Murphy B40D L.O. / R.F. Alignment with scale

Is the B40, then, the source of those NOS 4-gang capacitors with the thick ceramic shaft that appeared on the market several years ago?

David
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Old 27th Jul 2015, 5:45 pm   #23
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Default Re: Murphy B40D L.O. / R.F. Alignment with scale

I wonder? It's the sort of thing (well, actually, there's lots of disparate things) that might have been laid down in stores in big numbers because of initial anecdotal attrition at considerable expense to thee and me, then got dumped on the surplus market at very low price. I don't suppose that a large and very heavy radio that might have been bumped up and down hatchways and ladders and bashed about through tight spaces went very well with a ceramic shaft! Pye's CAT receiver also has a thick ceramic shaft four-ganger, but it's not as self-destructively large and heavy....

As in

www.retro.co.za/zs1ke/Type619-CAT/Top.jpg

Last edited by turretslug; 27th Jul 2015 at 6:06 pm. Reason: Illustration of tuning cap found.
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