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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 19th Sep 2021, 10:15 pm   #21
mrrstrat
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Default Re: Hallicrafters SX-17 Advice on repair.

I have never seen the caps that I replaced ever fail - I guess everything is fair game in these sets. I did order some replacement filter caps and a score of 10pF/500VDC dipped mylars and may replace all of the 10pFs as this is my personal set.
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Old 22nd Sep 2021, 2:38 am   #22
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Default Re: Hallicrafters SX-17 Advice on repair.

Anyone have any good clues on strengthening a very weak BFO on the SX-17? I have thousands of tubes and picked a very strong set - figured that would make the BFO work better. No improvement...
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Old 22nd Sep 2021, 8:44 am   #23
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Default Re: Hallicrafters SX-17 Advice on repair.

As a prewar set, the BFO was there only to provide a beat note for CW, not for SSB resolution. You might want to consider a product detector modification. There were plenty of such articles around in the '50s-'60s, possibly even SX-17 specific ones.
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Old 22nd Sep 2021, 1:50 pm   #24
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Default Re: Hallicrafters SX-17 Advice on repair.

The BFO injection on the one I had worked ok on CW and SSB.

Some shots of the front panel refurbishment I did, not an easy job as the lettering is raised, in my case they started out as raised rust, I managed to remove it back to the metal (not a lot to play with) then varnish.
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Old 22nd Sep 2021, 2:14 pm   #25
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Default Re: Hallicrafters SX-17 Advice on repair.

Its a beauty Lawrence!

My fathers SX-16 has great BFO and can SSB. That is not to say it was not modified as it when I got it the set looked like it was full of ceramic caps from the 60s in it from an (much) earlier repair.

I am hunting down sources of weak signal - the dog house the 6J7 sits on has nearly no extra wire slack to move it very far, but all I saw was two resistors in it and they appear to be in spec. The voltages on the 6J7 with my 1000R/V meter reveals voltages are in the ballpark (as per the manual).

The 6J7 tests strong - I checked my 6R7 and it is 92/48 triode, and 42/40 and 44/40 diode on my calibrated TV-7. So its not likely the valves and possibly a feed to them (or the coupling between them). I just want it to work in spec - it is so weak that I can only hear a faint reference to it on medium wave. I did mess with the transformer for the BFO by adjusting it a little on a station and modulated the controls - this helped a little to get a pitch but again it is so faint it is not even an effect on the signal.

And: I have not aligned it yet at all but tweaked some of the caps and padders to see if I have any issues to work out before a real alignment attempt. The medium wave band with AVC on and XTAL in produces some rich and full sounding local AM (Chicago stations come is like its next door with 10 foot of 22 gauge wire in a basement - so I am encouraged the set can work well).



Quote:
Originally Posted by ms660 View Post
The BFO injection on the one I had worked ok on CW and SSB.

Some shots of the front panel refurbishment I did, not an easy job as the lettering is raised, in my case they started out as raised rust, I managed to remove it back to the metal (not a lot to play with) then varnish.
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Old 22nd Sep 2021, 2:16 pm   #26
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Default Re: Hallicrafters SX-17 Advice on repair.

If you happen to have links to such articles handy please send them - I may be up for a mod if it does not involve adding another valve to the set.

Quote:
Originally Posted by Herald1360 View Post
As a prewar set, the BFO was there only to provide a beat note for CW, not for SSB resolution. You might want to consider a product detector modification. There were plenty of such articles around in the '50s-'60s, possibly even SX-17 specific ones.
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Old 23rd Sep 2021, 9:48 am   #27
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Default Re: Hallicrafters SX-17 Advice on repair.

Sorry, can't help with specifics. A PD mod would definitely require additional active devices, though, either hollow or solid state!

If the BFO's as weak as you describe, it does sound as if something's amiss. Maybe finding another user of your specific model, maybe from across the pond, would be helpful.
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Old 23rd Sep 2021, 12:45 pm   #28
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Default Re: Hallicrafters SX-17 Advice on repair.

You could try this as a basis:

http://www.isquare.com/millen/Articles/hropd.html

Ditch the 6H6 and use its heater supply, you might be able to sub the 6BE6 with an octal based heptode, you could try a solid state diode for the noise limiter or replace the 6R7 with a suitably rated double triode (separate cathodes) and strap one of the triodes as a diode and use that instead.

Lawrence.

Last edited by ms660; 23rd Sep 2021 at 1:00 pm. Reason: extra info
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Old 24th Sep 2021, 1:42 am   #29
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Default Re: Hallicrafters SX-17 Advice on repair.

I did figure out the BFO issue: turned out that the little box under the BFO valve had a couple capacitors I needed to replace. With an adjustment to the BFO transformer now it is strong and alive! So I'll leave it.

I am wondering: is there a good way to tap a line within the set with a VOM to better detect IF alignment? I use the method in the many SX-28s I have worked on by tapping across R25 the audio detector load resistor to detect max deflection. Would this work with the SX-16 (I have not tried).

Last edited by mrrstrat; 24th Sep 2021 at 1:49 am.
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Old 24th Sep 2021, 8:31 pm   #30
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Default Re: Hallicrafters SX-17 Advice on repair.

I figured out that using the AGC line via R14 and a high impedance meter worked great to peak my IFs to the derived frequency of my XTAL.

This is a similar method in the SX-28 I have used and it appears to work.
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