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Old 22nd Jun 2024, 4:54 pm   #1
DonaldStott
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Default IFT Screening Can

I'm missing the screening can for the 1st FM IFT on the radio I'm currently restoring - Murphy A272C. These seem to be of a standard size (?) so I'm hoping someone out there has something suitable. The other IFTs appear to have a 'celluloid type' internal sleeve as well.

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PM me please if you have a spare screening can of this type and size - happy to pay costs and p&p.
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Old 23rd Jun 2024, 6:41 am   #2
Gabe001
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Default Re: IFT Screening Can

Have you seen this thread

https://www.vintage-radio.net/forum/...d.php?t=212010

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Old 23rd Jun 2024, 9:13 am   #3
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Default Re: IFT Screening Can

Quote:
Originally Posted by Gabe001 View Post
Thanks Gabriel
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Old 23rd Jun 2024, 9:16 am   #4
Leon Crampin
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Default Re: IFT Screening Can

Are you sure there's one missing? On this chassis, the AM aerial coils assembly has no can by design, whereas the first FM IF coil assembly does. These cans frequently get swapped over, for some reason.

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Old 23rd Jun 2024, 11:09 am   #5
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Default Re: IFT Screening Can

Quote:
Originally Posted by Leon Crampin View Post
Are you sure there's one missing? On this chassis, the AM aerial coils assembly has no can by design, whereas the first FM IF coil assembly does. These cans frequently get swapped over, for some reason.

Leon
Thanks Leon, understood - I just assumed that as the AM aerial coils assembly and the 1st FM IFT had the same bases then a screening can was missing: -

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Old 23rd Jun 2024, 2:56 pm   #6
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Default Re: IFT Screening Can

My parents bought a 272C new in ca. 1956, I'm sure it was 'installed' by the retailer's engineer, who whipped the back off, removed the aerial can, and explained that it avoided needing an external aerial. I've remained impressed at the sensitivity of the set, as it then had a ferrite rod in the form of about an inch of ΒΌ" ferrite inside the coils, and would receive the near continentals all day on LW, and didn't really benefit from an external aerial.
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Old 24th Jun 2024, 8:13 am   #7
Leon Crampin
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Default Re: IFT Screening Can

Check the Murphy A272C service data before speculating about can removal. On this chassis, the FM aerial also serves as an AM aerial in a balanced input arrangement.

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Old 25th Jun 2024, 12:17 am   #8
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Default Re: IFT Screening Can

That sounds like a better reason for the good AM reception without an external wire aerial.
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Old 25th Jun 2024, 7:46 am   #9
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Default Re: IFT Screening Can

Here's a photo of the chassis in an A272C and an A272.
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Old 25th Jun 2024, 5:04 pm   #10
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Default Re: IFT Screening Can

And here is a photo, slightly blurred, of the A272C chassis from the Radiomuseum site: -

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Old 26th Jun 2024, 11:41 am   #11
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Default Re: IFT Screening Can

I am of course taking the advice of Forum members that '... the AM aerial coils assembly has no can by design...' (Leon Crampin) but of course I'd like to know why as the coils seem very exposed to me - see picture in my Post #5 above?
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Old 1st Jul 2024, 11:32 am   #12
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Default Re: IFT Screening Can

The Radiomuseum photo seems to confirm my recollection, and my guess is that this model was usually delivered without the RF can because its removal would necessitate re-aligning, which the engineers would usually have already done in the workshop.

Coincidentally, I've just unearthed one of those electrolytics with the top-up bungs, saves me having to ask what they would have been used in.
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Old 1st Jul 2024, 4:54 pm   #13
Leon Crampin
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Default Re: IFT Screening Can

Page 6 of the Murphy service manual for the A272C gives a line drawing of the upper chassis view. The AM aerial coil is shown just as a crosshatched circular bare coil, wheras the FM IF coils assemblies are drawn with a circle around them - denoting a can.

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Old 2nd Jul 2024, 12:54 am   #14
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Default Re: IFT Screening Can

Really? In that case, I withdraw my, um, case. it's too long ago to remember properly and was long before I developed a technical interest in Radio. The Radiomuseum guy may have borrowed a can for his restoration, assuming it was missing.

I wonder if it would be possible to tune the LF end correctly with a can on?
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Old 2nd Jul 2024, 9:50 am   #15
DonaldStott
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Default Re: IFT Screening Can

Quote:
Originally Posted by Leon Crampin View Post
Page 6 of the Murphy service manual for the A272C gives a line drawing of the upper chassis view. The AM aerial coil is shown just as a crosshatched circular bare coil, wheras the FM IF coils assemblies are drawn with a circle around them - denoting a can.

Leon.

Thanks for that - understood.

Indeed Page 3 of the Trader Service Sheet 1413 for the Murphy A272 makes it very obvious!
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Old 2nd Jul 2024, 9:55 am   #16
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Default Re: IFT Screening Can

As this can is no longer required I will close this wanted thread.

Cheers

Mike T
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