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Old 20th Oct 2020, 9:26 am   #21
falcon123
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

As I've stirred such a hornet's nest, I don't think I've the heart to tell you all that it has been resolved and the error was entirely my fault. What a long strange trip it's been. Anyway here's the story. It would seem that the threaded shaft is long enough and the coil wound on the tube just far enough away on a tube also long enough that it's possible to actually screw the slug PAST its resonant point where it starts to peak again as the core moves inward but as this inward movement has its limits it wouldn't peak. On a whim with no success earlier today I elected to back the slug completely out against its stop. This design leaves more than 1'' of threaded rod standing above its nut. With the generator on the set and warmed for two hours previously playing on AM b.c. I set it up to run the IF alignment again. In the AM alignment the 2nd IF primary is the 3rd adjustment. Lo and behold it peaked just fine with about 5/8'' of stud protruding. The rest of the alignment progressed without issue. My only defence is this range of adjustment seems unnecessary and set me up for
the fall. I will remember this when dealing with Hallicrafters' IF transformers in the future, but IT'S FIXED!!! and that's what counts and I learned some things along the way and thats a PLUS. I wish to thank all you folks who responded. In the future I'll try to be better prepared for class. Regards, John.
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Old 20th Oct 2020, 9:49 am   #22
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

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Presumably the effect can be avoided by switching off the AGC?
You could do but I would always keep the signal input as low as possible, that's the way I've always done it unless instructed otherwise.

Lawrence.
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Old 20th Oct 2020, 12:08 pm   #23
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

The best fix of all is the one that was never broken lol. The guys here brought up loads of great information as always to heliport
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Old 20th Oct 2020, 1:51 pm   #24
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

I've been following this thread with interest, very entertaining! I suppose the final solution tells us why some manufacturers tell us to use the first peak we come to when twizzing in a certain direction.
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Old 20th Oct 2020, 3:48 pm   #25
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

An inductor in an IFT is set to be too low L on its own. So that an adjustment slug can be added to shift the L either side of nominal. So the slug can take the L a bit too high or a bit too low.

So correct adjustment will have the slug stuck out of the coil. It could be either side and still get the same L.

Now, an IFT has two of these coil/slug arrangements.

Each can get the right L with its slug in either of two positions.

However, the slug hanging out on the side nearest the other coil increases the coupling to that coil. This applies to both slugs and there are four combinations.

USUALLY the wanted setting is witht he slugs extending outside their coils and away from each other. Designers choose this to get their wanted amount of coupling without needing a bigger IFT to space the coils more.

Hence the usual instruction to go for the first peak as you fit the slug from the outside.

David
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Old 20th Oct 2020, 11:18 pm   #26
falcon123
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

i didnt realize there could be a 2nd peak. but i sure found out differently. i recapped the transformer and adjusted it from whatever the previous "fixers" had left it. i think from now on i will back them out to there limits and go from there.
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Old 21st Oct 2020, 9:31 am   #27
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

2nd peak of Osc trimmers on some shortwave bands in some receivers can also lead to a merry dance, someone had one recently here on this forum where by the trimmer had an adjustment range that covered both osc above signal and osc below signal, it had been peaked to below signal instead of above.

That effect is pointed out in some receiver manuals but not in others.

Lawrence.
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Old 21st Oct 2020, 1:27 pm   #28
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

This also makes me re-think the alignments I have done to my own sets. I do remember the instructions for two of my sets say to look for the beat peaks and I was not entirely sure as to why. But what David says now has those instructions that make sense now.

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i didnt realize there could be a 2nd peak. but i sure found out differently. i recapped the transformer and adjusted it from whatever the previous "fixers" had left it. i think from now on i will back them out to there limits and go from there.
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Old 21st Oct 2020, 1:36 pm   #29
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

I had just this scenario when aligning the IF of an Eddystone 670A a wee while back- all the cores were well recessed down and one in particular showed soggy and indeterminate change when rocked either side of existing setting, almost as far down as it could go. Starting from scratch and winding the cores right back out quickly gave definite peaks with all cores much further out than previously, on-air use confirmed good gain and satisfactory bandwidth. (The output valve's 220 ohm cathode resistor had also been changed to 100 ohms- presumably the previous owner was disappointed that UL41s weren't being consumed fast enough- and they'd managed to defeat the inner-chassis-to-outer-metal-case isolation in not one but two places.... Never be too surprised at what has been done to something that's been around for a few decades).
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Old 21st Oct 2020, 1:41 pm   #30
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

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2nd peak of Osc trimmers on some shortwave bands in some receivers can also lead to a merry dance, someone had one recently here on this forum where by the trimmer had an adjustment range that covered both osc above signal and osc below signal, it had been peaked to below signal instead of above.

That effect is pointed out in some receiver manuals but not in others.

Lawrence.
Definitely! Up at 30MHz-odd, a small swing of the trimmer can cover a huge range of oscillator frequency, don't miss that quick plip and be sure it's the right one, very much safe-cracker's fingers stuff.
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Old 21st Oct 2020, 1:55 pm   #31
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

I got a couple of trimmers and pads on my SX-110 that must be ninja/expert-level. The blip is within a turn less than a human hair (and that was after it was cleaned). I found it was best to try to pull back and 'land' on it rather than try to creep the screw setting to it.

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Quote:
Originally Posted by ms660 View Post
2nd peak of Osc trimmers on some shortwave bands in some receivers can also lead to a merry dance, someone had one recently here on this forum where by the trimmer had an adjustment range that covered both osc above signal and osc below signal, it had been peaked to below signal instead of above.

That effect is pointed out in some receiver manuals but not in others.

Lawrence.
Definitely! Up at 30MHz-odd, a small swing of the trimmer can cover a huge range of oscillator frequency, don't miss that quick plip and be sure it's the right one, very much safe-cracker's fingers stuff.
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Old 21st Oct 2020, 10:37 pm   #32
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

certainly this forum is a much nicer place than the one i just left.(which will remain annonymous. isnt that so mr,strat
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Old 22nd Oct 2020, 12:45 am   #33
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

I'll agree with that - this forum is very helpful and I have been able to help the contribute myself. Lots of very sharp radio guys on this forum that are glad to help

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certainly this forum is a much nicer place than the one i just left.(which will remain annonymous. isnt that so mr,strat
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Old 22nd Oct 2020, 12:45 am   #34
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

if you are talking about mica ceramic trimmers a bit of lube on the thread eases things as it takes the jump out.
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Old 22nd Oct 2020, 11:55 am   #35
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

Let's chuck in one more thing about receiver alignment, affecting classic comms receivers.

Some sets like the better Hallicrafters, the AR88, HRO, etc have switched selectivity with some setting adding a crystal half-lattice filter into the mix for a nice narrow bandwidth for CW reception.

The crystals weren't made any more accurately than they needed to be for this fairly undemanding application, also people setting up the LC bandwidths often relied on the markings of their sig gen and could be a bit off.

The result is that the IF peak shifts when you engage the crystal and peaking on the crystal might be a bit down on the LC filtering shape.

The solution is to tune up the LC stages to suit the unadjustable crystal. You may not be dead on the specified IF number, but at least all resonators are singing the same song in the same key.

It gives you the freedom to switch the bandwidth narrower without having to find the signal again.

So good alignment instructions have you do the crystal ranges first.

David
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Old 22nd Oct 2020, 11:59 am   #36
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

Some recommended making a test generator for alignment from the Xtal fitted to the receiver.

Lawrence
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Old 22nd Oct 2020, 12:18 pm   #37
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

There's a certain logic to that, but the oscillator doesn't necessarily pull the crystal to quite the same frequency that the filter circuit does, and it's a bit of a beggar trying to use the crystal in two places at once if you want to check all your bandwidths centre up.

So I'd opt for leaving the crystal in situ, and setting the sig gen to agree with it. Then you set the LC stages to agree with the sig gen.

Working progressively wider means that with subsequent adjustments having less room to manoeuvre there is less importance to be dead on with the wider bandwidths.

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Old 22nd Oct 2020, 12:32 pm   #38
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

Very little difference when using the receiver's Xtal for a signal generator oscillator......According to the Hallicrafters SX17 manual.

I happened to own one of those receivers....to be honest I preferred it to My SX28's and AR88.....but not my HRO's.

Lawrence.
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Old 22nd Oct 2020, 12:33 pm   #39
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

this particular hallicrafters wants the crystal frequ, determined FIRST,then this actual setting is used to align the i.f. i'm told that anything within 5 kc is ok but the the closer to 455kc the better,there's even a procedure for taking the crystal apart to clean the actual quartz.mine was well within range.my sx-42 uses the same procedure.
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Old 22nd Oct 2020, 12:37 pm   #40
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Default Re: Hallicrafters SX-43 2nd I.F. won't peak

Plus or minus 5kHz is an awfully wide range.
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