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Old 18th Dec 2006, 2:26 pm   #1
Keith
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Default Hallicrafters S27 coil info required

I recently aquired the above receiver but it seems that someone has been in there and modified the range 3 (high range) oscillator coil. This may be connected with the fact that the oscillator stops below about 95MHz (received frequency). Does anyone out there have details of the 3 windings of this (self supporting) coil. i.e. number of turns/diameter/spacing/gauge for the tuned winding/feedback/output coupling. A photgraph would be most useful although the coil is rather buried (and under a cover). Thanks in anticipation.

Keith
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Old 18th Dec 2006, 6:17 pm   #2
dave walsh
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Default Re: Hallicrafters S27 coil info required

Can't do the info unfortunately Keith but I know that these were sometimes "tweaked up to cover all of the 2 metre band which might explain the oscillator discrepancies! I'm sure I've seen some Hallicrafter stuff recently but can't recall where on the web. Cheers Dave
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Old 23rd Dec 2006, 2:12 am   #3
peter_scott
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Default Re: Hallicrafters S27 coil info required

I have an S36A and its manual which gives good descriptions of number of turns, former size and wire diameter for its coils and transformers. I don't know if the 36A and the 27 are the same regarding these parts but BAMA seems to have the S27 manual.

If you want to post a photo of what you want to see then I can try to replicate it with the 36A if this is of any use.

Peter.
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Old 26th Dec 2006, 11:49 pm   #4
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Default Re: Hallicrafters S27 coil info required

Peter,

Thanks for the reply. I suspect the S27 and S36 are pretty similar in this area so any info would be appreciated. I have attached pictures of the relevant oscillator (T9), RF (T6) and aerial (T3) coils. T9 and T6 have certainly been got at - not sure about T3. I would be most grateful if you could let me have the correct coil details. As Dave comments, they may well have been changed to get the coverage up to 146MHz.

Keith
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Old 27th Dec 2006, 1:15 am   #5
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Default Re: Hallicrafters S27 coil info required

Hi Keith,

Sorry, getting meaningful angles on the photos is a bit tricky but here they are anyway. The Hallicrafters descriptions from the parts list may be more helpful. Photos are T3, T6, T9, another T3 angle.

Peter
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Old 27th Dec 2006, 1:17 am   #6
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Default Re: Hallicrafters S27 coil info required

and another shot of T6
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Old 27th Dec 2006, 11:36 am   #7
Keith
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Default Re: Hallicrafters S27 coil info required

Peter,

Thank you so much for the photos and data. I can't believe how quickly you responded! It certainly confirms that the coils have been altered - they're supposed to have formers for a start! I think its time to strip out the front end and do some serious de-modifying.

Many thanks again,

Keith
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Old 29th Dec 2006, 9:41 pm   #8
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Default Re: Hallicrafters S27 coil info required

Peter,

I'm afraid I'm still a bit confused with the coil data you kindly sent me. My problem is deciding what is meant by the terms primary, first secondary and second secondary in the description of T9. By calculation, even the largest winding (1.5 turns) doesn't seem to give enough inductance to resonate with the ~60pF at the required 77.5MHz (83 minus 5.5MHz IF). I wonder if I could ask you to copy me the T9 data for the range 2 coils (which appear undisturbed in my RX). This would hopefully allow me to establish which winding is which (assuming the descriptions are consistent).

Best regards,

Keith
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Old 30th Dec 2006, 10:25 pm   #9
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Default Re: Hallicrafters S27 coil info required

Hi Keith,

Sorry if this is proving confusing. Looking at your S27 schematic it doesn't appear too different to my S36A. I assume the primary of T9 is the winding connected across C1c / C11. I don't know what the trimmer size is but your 60pF seems about right given that C1c is 54 pF. I assume by "T9 data for the range 2 coils" you mean T8 data.

HTH,

Peter.
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Old 30th Dec 2006, 10:28 pm   #10
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Default Re: Hallicrafters S27 coil info required

Have added a close up of the T9 area.
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Old 31st Dec 2006, 11:24 am   #11
Keith
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Default Re: Hallicrafters S27 coil info required

Peter,

Thank you very much for the additional info. Yes, it was the T8 data that I needed. I think I can deduce from this which secondary is which and hopefully apply this to the rebuild of T9. Although the FM brodcast stations are appearing in about the right place on the dial, I measure the oscillator frequency as being on the high frequency side of the signal frequency which I believe is incorrect. I suspect that someone has perhaps attempted to return the range to its original coverage and not quite got it right. Anyway I shall persevere and let you know how I get on.

Best regards and a Happy New Year,

Keith
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Old 31st Dec 2006, 3:16 pm   #12
peter_scott
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Default Re: Hallicrafters S27 coil info required

Hi Keith,

It's about five years since I turned mine on but after swapping some acorns I've got the oscillator running. It appears to have the oscillator above the received frequency for band 1 and below the received frequency for bands 2 and 3. I missed that in the manual first time around but I now see that the circuit description confirms this.

Happy New Year,

Peter.
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Old 31st Dec 2006, 8:00 pm   #13
Keith
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Default Re: Hallicrafters S27 coil info required

Hi again,

Still struggling I'm afraid!

By comparing my T8 with the data, it's clear that what is referred to as the "primary" is in fact the grid feedback winding (3/4 turns). The tuned anode winding is called the "first secondary" (2-1/2 turns). Using this logic on T9 I produced a coil with a 1 turn tuned winding and a 1/2 turn grid feedback winding. This failed to oscillate. Increasing the feedback winding to just over 1 turn gave me oscillations but still too high in frequency (by ~10MHz). The oscillations still die below ~95MHz.

I'm beginning to think there may be differences in T9 between the S36 and S27. This is supported by the fact that the tuning capacitor C1 is quoted as 47.5 pF max (no trimmer) in the S27 as compared with 54.5pF (plus a trimmer) in the S36. consequently the S27 would need more inductance.

I shall continue to play around in the new year.

All the best,

Keith
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Old 31st Dec 2006, 9:17 pm   #14
peter_scott
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Default Re: Hallicrafters S27 coil info required

Hi Keith,

Unfortunately the S27 manual on BAMA is abridged however this looks like it should be the complete thing with coil descriptions.
http://cgi.ebay.com/Hallicrafters-S-...QQcmdZViewItem

Peter
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Old 31st Dec 2006, 10:05 pm   #15
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Default Re: Hallicrafters S27 coil info required

Sorry I suggested the eBay one. I suspect it is the same as the BAMA one.

Here's an easily viewable copy of the S36A manual http://www.nostalgiaair.org/PagesByM...0/M0008860.pdf


Last edited by peter_scott; 31st Dec 2006 at 10:20 pm.
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Old 11th Jan 2007, 6:35 pm   #16
Keith
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Default Re: Hallicrafters S27 coil info required

Peter,

Just an update on the S-27. By judicious fiddling I've discovered that the frequency range and stability of oscillation is very dependent on the proximity of the feedback winding to the tuned winding. For range 3 these need to be virtually co-located. I have now got the coil almost right - just a bit more tweaking required. Unfortunately, it's currently wound on a modern clear plastic former as that was the only 3/8" diameter I could find. Hopefully I will come across something that looks a bit more like bakelite in the future. Now I need to tackle the input and mixer coils so that I can get the tracking in - 1/4" formers should be easier to find!

Thanks again for all your help,

Keith
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Old 11th Jan 2007, 8:46 pm   #17
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Default Re: Hallicrafters S27 coil info required

Hi Keith on some radios the coils are actuall interwound to maintain oscillation, usually at the bottom (earthy) end of the main coil. Try this and see if it helps.

Ed
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