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HQ-170 Alignment




 
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n5op
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« Reply #25 on: October 04, 2013, 11:50:37 AM »

Assuming it will take about a week for parts to arrive, I ordered a full compliment of replacement sliver mica capacitors for the sideband selection switch. I may be able to get away with replacing only those on the LSB side, if I could figure out the switch position shown on the schematic. The notation says "Sidebands Shown in upper pos. (panel knob indicates lower pos.)" How's that again?

Kim N5OP
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n5op
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« Reply #26 on: October 04, 2013, 11:52:13 AM »

No worries, Pete. Heck, I got nuthin' but time right now...

Kim N5OP
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n5op
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« Reply #27 on: October 04, 2013, 02:03:51 PM »

I'd be surprised if what I'm seeing is normal. Recall that I did similar tests with an external source and found that the LSB position was quite a bit narrower than the USB position. That the difference be imes striking at awvtivity settings of 2 and 3 kHz is, to my thinking, anyway, partcularly telling.

These are rather easy tests to make because what's being done is a "sweep" of the rx passband essentially by ear. In a properly aligned sine sideband rx, sweeping a carrier through a single side band will result in a sweeping tone. The signal strength is a function of tone frequency, filter skirts and bandwidth. If the passband has "brick wall" skirts, is 2700 Hz wide and passes frequencies spanning 3000-300 Hz, then the same frequencies should be heard in both sidebands. A tone of 3001 Hz or 299 Hz would vanish because they come from a carrier outside theRX passband.  If the carrier starts low and sweeps upward through the LSB, the tone will start high and sweep low. The opposite will occur in thee USB.

At least that's how I figure it and it's what happens in my TS-930S and Orion II receivers.

Kim N5OP
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k7pp
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« Reply #28 on: October 04, 2013, 07:00:32 PM »

OK, Kim;

Can you check this one out and comment?

Best,
Pete

http://www.youtube.com/watch?v=75nOZJIxPRc
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n5op
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« Reply #29 on: October 05, 2013, 10:27:51 AM »

Well done video, Pete. I like seeing the passband move across the signal Smiley

Like yours, I see a weak response in the opposite sidbeand. UNlike yours, I never hear any tones even close to 3000 Hz in the LSB position but I DO in the USB position. Your sidebands respond symmetrically while mine do not. Mine is NOT balanced on both sidebands. We're looking at MUCH worse performance than yours.

The asymmetry between sideband response becomes most striking at selectivities of 2 and 3 kHz. There is negligible asymmetry in the 0.5 and 1 kHz selectivity settings.

I looked at the sideband selection switch and replacing any of the three capacitors hanging off of it is trivial. To replace any capacitors on the selectivity switch will require disassembly. How do I do that?

Kim N5OP
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n5op
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« Reply #30 on: October 05, 2013, 02:08:23 PM »

I've been studying the switch assemblies. All of the contacts have plenty of spring tension and all are intact. So there appears to be no obvious mechanical problems.

These switch assemblies can be removed, or at least dismounted and moved around a bit and were certainly not constructed in place. The 1/4" shaft from the knob goes into some sort of brass coupler to the keyed shaft that turns the movable contacts of the switch. All of this is mounted on a small subframe that provides mechanical stability.

I could go two slightly different ways, here. I could dismount the subframe and move the entire assembly towards the rear, get the shaft extensions free and move the assembly around as needed. That will be about awkward because of the long extensions but tractable. The second way is similar, but made easier if I can remove the 1/4" round shaft extensions. The second way may require removal of the indexing cam, and getting it back together could be... Sporting. Anyone with experience doing this on a similar receiver, feel free to chime in.

Kim N5OP
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k7pp
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« Reply #31 on: October 06, 2013, 12:02:55 AM »

Hi again,  Kim;
Just got back from an all day Car show and saw your post. 
Before talking about pulling out switches, can I ask you to check one more thing?
Hope you don't think I'm a nut case but can you look at the notch filter and make sure that you get your notch in the middle of the range (0) by using the calibrator and once you verify that,  move the notch adjustment fully clockwise.
I just want to make sure that the notch filter isn't miss-adjusted and causing your symptom.
If you are satisfied that it is not part of the problem then, perhaps, one more check.
Check the alignment of "L4".  This can be done is step 3 of the service manual.
If this is off,  it is possible it could cause your symptom.
Keep in mind that L4 has three different peaks.   The largest of the peaks being the correct one.
If L4 is not centered on the proper peak, you could tune all day and not get the symmetry on both sides of your received signal.

That aside,  I'm going to have to agree that you may indeed have a bad cap.
I'll take another look at my receiver and let you know if I have any worthwhile comments.   I think you already know that the low IF string is shifted slightly to detect the upper and then the lower sideband.
The ganged wafer switches add or subtract values that shift each transformer stage all at once.  It would have been easier to use a crystal filter but it is what it is.

Pete
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n5op
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« Reply #32 on: October 06, 2013, 01:06:17 PM »

I'm pretty sure the slot is aligned, but I'll double check. I was utterly unaware that adjusting L4 could result in 3 different peaks. I've never e pediments experienced more than one, but it could have been mis-aligned arly on, so I'll check for that. IC those pan out, I've figured out how to get room to work on the assemblies and it won't be too terrible if I can gt enough room to work.

Thanks, Pete!

Kim N5OP
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W3GMS
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« Reply #33 on: October 06, 2013, 02:19:06 PM »

I have really enjoyed keeping up on this thread!  With all this great material we need to capture it in one documents so others can use it.  I have a 170 and although mine is in very good shape cosmetically, I am sure it will need some under the hood time. 

Thanks,

Joe, W3GMS
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n5op
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« Reply #34 on: October 06, 2013, 08:29:18 PM »

I don't recommend archival until we've figured out what the problem is Smiley

Figuring out how the switch assemblies were installed was interesting two wires prevent me from getting it free. All others were left dressed such that the assembly could be greed from the front of the chassis. I suspect a shift change resulted in a slightly different dressing technique because a different tech finished the assembly wiring.

I'll have to disconnect two wires to two different IF transformers. To free the assembly enough to work on it. Even then, it will be tight.

I suspect Hammarlind didn't use crystal filters due to cost. There were no monolithic crystal filters back then -- all crystal filters were discrete and were built and matched by hand. It's actually pretty impressive what was done with LC circuits. It's not as good as crystal filters, but still pretty danged good!

Kim N5OP
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nq5t
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« Reply #35 on: October 06, 2013, 09:15:18 PM »

It seems to me this is taking an extreme turn that might not be necessary. 

1.  Response switching in the HQ-xxx 60 Khs IF strip was never MIL-spec. 

2.  You need to do measurements of response with the AGC OFF!! and an RMS voltmeter on the output, making sure the input levels don't overload anything.  The S-meter is inaccurate to the point of being useless.   If you don't have an analog RMS voltmeter, get one .. many on eBay for non-absurd pricing.

The best way to align one of these (or anything else for that matter) is with a sweep generator and a scope.  Beg/borrow/steal one.  If not, then align it by the book, adjust the 455 -> 60Khz bandpass oscillator for the best match between LSB/USB and move on to the next project.  I've done a half dozen of these things (HQ-170/180/HC-10) and never had to fiddle with the switches, or the caps, or anything in the IF bandwidth circuits.  I'm not saying that you might not be able to marginally improve things. but you have to consider the return ...

Grant NQ5T



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nq5t
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« Reply #36 on: October 06, 2013, 09:24:40 PM »

I suspect Hammarlind didn't use crystal filters due to cost. There were no monolithic crystal filters back then -- all crystal filters were discrete and were built and matched by hand. It's actually pretty impressive what was done with LC circuits. It's not as good as crystal filters, but still pretty danged good!

Kim N5OP

Well .. not so much.  LC circuits have some advantages. The real question I've always had is why Hammarlund/Halli didn't add just one more stage with a couple more tuned circuits to improve the skirts a bit.  You won't find a crystal filter, or even a hallowed mechanical filter that will out do something as pedestrian as a BC-453 on skirts (relative to the era).  And the real benefit of an LC circuit is reduced group delay and distortion.  It's why AM'ers generally prefer an R-390 over an R390A.  It's quite possible to build an LC filter that will put a crystal filter to shame (if you can find the parts today) -- but the LC filter might be MORE expensive.  Obviously, YMMV, depending on a lot of stuff ... Smiley
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k7pp
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« Reply #37 on: October 07, 2013, 02:35:05 AM »

I'd have to agree with some of Grants comments in that there are better but not always easier ways to trouble shoot problems like this.
It's one of the reasons I spent so much time trying to trouble shoot the issue using the receivers own meter and filters to narrow things down. 
Of course there are better ways to proceed IF, you have the proper test equipment.
Many hams do not have the required test equipment needed to do advanced troubleshooting and that puts them in a position to either have to borrow it,  have it done and perhaps pay for it or to shot gun the components in the circuit.

If it's possible to avoid the shotgun method, you might save yourself allot of trouble.  Even after you shotgun,  you still have to revisit the alignment issue.

 I might attack this a bit differently on the bench at my shack as it is fairly well equipped with the necessary test gear and start, as Grant suggested, with a sweep of the low IF and then take a scope and work your way down the 60 khz amps and look to see where the response goes bad.
I've also had pretty good luck using my frequency selective voltmeter to supplement past troubleshooting efforts.
If it's not an alignment issue to begin with then your choices become very limited.

I might also add that the "by the book" alignment does not call for a sweep alignment of the low IF.  They have you inject 60 khz and peak each of the transformers with the AVC disabled and an DC VTVM or equivalent to measure
the negative going voltage on the AM detector tube.  This seems fine for receivers that aren't having a problem but doesn't really tell you anything about the conditions Kim is encountering.

So,  that leaves Kim at an interesting crossroad.  The tests he's done seem to confirm a technical issue in the low IF.  He can borrow or buy the test equipment needed to inject a sweep signal into one or more stages and look at the response on a scope which should uncover the culprit or he can assume a faulty capacitor and shotgun them all without the need for buying or borrowing test equipment.

As many Hammarlunds as I've fixed over the years,  I've never had to delve into a component fix on the low IF so I have no worthwhile culprits to point my finger at.
Kim, If you can obtain the necessary test equipment and chose to do a stage by stage evaluation to trouble shoot this problem I could do a video showing a suggested procedure as I do have a sweep generator and scope as well as a frequency generator source.
If you decide on a wholesale replacement course of action, I'm sure we'll all still be here if you need further input.

Perhaps some of the other folks on the board might be interested in doing something similar regarding posting a troubleshooting procedure as well. 
I use an Iphone 5 for all of my YouTube videos and post directly from the phone to YouTube right there in the workshop.  I'm kind of an old geezer so I had to have one of my kids show me how.....LOL.

Best,
Pete



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n5op
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« Reply #38 on: October 07, 2013, 10:53:25 AM »

The alignment was done by "the book" using Issue No. 5, for serial numbers beyond 3800. Unfortunately, I have a malevolent sister who destroyed the original manual, so this is a replacement manual. I don;t know the serial number of the receiver, as I can't seem to find one anywhere. I know it was purchased in June 1959. Regardless, Issue No. 5 is "the book" I used for the alignment.

As per the manual, AVC was off and I took my readings across C44, a convenient place to access the output of the AM detector (and the point the manual recommends). Signal levels were kept in spec (no more than -1 VDC across C44). The point being that I didn't take any shortcuts.

That said, I am skeptical of passive component failures, especially silver mica failures. I don't have a service monitor, nor do I have a sweep generator. But W5JO has graciously offered me access to his sweep generator, so I think I'll take him up on it. If we find things truly wacked out by some sort of passive component failure, we'll find out for sure that way.

I don't expect MIL-spec performance from the old beast, but I know it can be better than what I'm seeing. I don;t understand what the problem is and I'm hesitant to simply start replacing stuff. If there's a problem, we'll uncover it and THEN fix it.

Kim N5OP
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« Reply #39 on: October 07, 2013, 05:00:14 PM »

Jim is justifiably concerned that such a procedure could take several hours and that we might have to leave it in mid-procedure, so he's going to loan me his tracking sweep generator. Pete, that means I'll need your video to show me how you think this should be done. So, I accept your instructional offer!

Kim N5OP
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k7pp
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« Reply #40 on: October 07, 2013, 06:52:36 PM »

OK,  Kim;
I'm going to need some time to pull the 170 out of the shack and get it up to the shop.   It will be fun to do as this 60 khz IF is common to several models and I've never done a sweep on the 170 before, but I do have a basic 170 so I can duplicate the exact radio you have. 
I think you are making the right choice and I'll do my best to get it onto a video.
I have done a sweep alignment on a 129-X which is currently on YouTube.

Pete

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n5op
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« Reply #41 on: October 10, 2013, 03:57:16 PM »

Hi Pete! I've jumped the gun on you and looked at the 60 kHz IF passband with a sweep generator. W5JO loaned me one as well, but I learned that the Elenco GF-8025 function generator that I recently bought out of an estate has sweep capability. Not only that, but it also has a sweep output that I can apply to the X channel of my Tektronix 2225 'scope so that the horizontal sweep is synced with the frequency. It's not the fanciest sweep generator, though, because I can't narrow down the sweep range very well, so it sweeps a broader range than I want. However, it's still easy to visualize what's going on.

I've attached several images I took of the passband -- all are at the same vertical sensitivity and none look like what I expect to see based on the manual. The vertical scale is 0.1 V per division and the sweep is about four per second to avoid any spurious high frequency components induced by the sweep itself. Signal injection is at the 3rd mixer and I pick off the signal at the AM detector, just as instructed by the manual for signal injection for alignment. AVC is off as is the BFO.

I played a bit with the 60 kHz alignment and I can change the shape of the passband and make it symmetric at 6 kHz bandwidths by selecting 3 kHz selectivity and "BOTH" sidebands, but I can't make it flat across 6 kHz. Making the passband symmetrical at 6 kHz bandwidth also screws up the sensitivity at narrow bandwidths making the receiver deaf as a post.  If I make the 6 kHz passband symmetric it retains a good-sized dip in the center and I still see the asymmetry between LSB and USB output. I cannot increase the USB output level while also lowering the LSB output level. 

After a complete "by the book" alignment, I get the following: image 1 is LSB at 0.5 kHz selectivity, image 2 is USB at 0.5 kHz, image 3 is LSB at 1 kHz. More images to follow...

Kim N5OP


* LSB_500Hz.JPG (1751.16 KB, 2592x1936 - viewed 393 times.)

* USB_500Hz.JPG (1847.92 KB, 2592x1936 - viewed 352 times.)

* LSB_1000Hz.JPG (1819.58 KB, 2592x1936 - viewed 386 times.)
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n5op
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« Reply #42 on: October 10, 2013, 04:01:12 PM »

More images: image 4 (in the series) is USB at 1 kHz, image 5 is LSB at 2 kHz, image 6 is USB at 2 kHz.

Kim N5OP


* USB_1000Hz.JPG (1993.18 KB, 2592x1936 - viewed 388 times.)

* LSB_2000Hz.JPG (1918.71 KB, 2592x1936 - viewed 356 times.)

* USB_2000Hz.JPG (1796.58 KB, 2592x1936 - viewed 433 times.)
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n5op
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« Reply #43 on: October 10, 2013, 04:08:55 PM »

Image 7: LSB at 3 kHz, image 8 USB at 3 kHz, image 9 BOTH at 3 kHz.

Besides "not right," what is this telling me about where to look for problems?

Kim N5OP


* LSB_3000Hz.JPG (1877.01 KB, 2592x1936 - viewed 323 times.)

* USB_3000Hz.JPG (1883.21 KB, 2592x1936 - viewed 387 times.)

* BOTH_3000Hz.JPG (1912.63 KB, 2592x1936 - viewed 354 times.)
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n5op
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« Reply #44 on: October 10, 2013, 06:51:18 PM »

I also want to reassure anyone interested that I went through a complete realignment of the 455 kHz (and ensured that I set L4 for the biggest peak) and 3035 kHz IFs, as well. While I found that the 455 kHz IF was a bit off and that getting it better enhanced the receiver sensitivity, it made no difference to the 60 kHz bandpass response.

Kim N5OP
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« Reply #45 on: October 10, 2013, 08:34:10 PM »

Oh, and finally: yes, I inverted the channel when I took those pictures. Those are, in fact, negative voltage traces.

Kim N5OP
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k7pp
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« Reply #46 on: October 10, 2013, 10:41:23 PM »

Wow,  You are way ahead of me,  Kim.
I haven't even cleaned my bench off yet.

Nice display pix.
The scope display seems to bear out your description of your problem.

Seems like the passband is working properly in the .5 position on both sidebands.  It's starting to appear as if the sideband switching might be normal and the capacitor or capacitors providing the pass band shift in one of the IF stages might have a problem.

Is it possible to move down the IF chain and inject at the grid of each amplifier tube and inspect the same sideband information?
You may come to a stage where anything down stream appears normal.

Also,  do you have a scope probe with a detector?  You might be able to test each stage independently.
One last question.  When you did the book alignment,  What sideband position were you using?
And,  another thought.  Notice the capacitors used in the band pass shift have a common connection and the other end goes to the wafer switch and are not connected to anything when not selected?  If you can connect a capacitor tester or even a simple ohm meter and un-select the cap being tested, you can check it for continuity.  Doesn't evey body has a little bit of Irish luck they can draw on from time to time?  Might find it right off the bat.

BTW, Nice work!
Regards,
Pete
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n5op
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« Reply #47 on: October 11, 2013, 12:29:28 AM »

Thanks, Pete!

Hmmm, lessee here...

Actually, if I get all the capacitors I need, its not that much more work to replace them all vs. replacing them piecemeal. The main work is in freeing up the switch assembly so as to be able to get to the capacitors.

No, I don't have a capacitor tester, especially anything that goes down to the capacitance values Hammarlund used. I have a Fluke meter that is suppose to do that, but I don't think it goes down to values that are small enough.

If I move down the IF chain, I wonder if I'd know when I found something odd? I sort of have to know what it should normally look like to know it's wrong. I'm seeing the entire response here -- if I'm unlucky enough to have two bad stages, that could get so confusing that I can no longer tell what's normal and what isn't.

No, I don't have a detector probe.

To do the ohm meter trick, I still need to dismount the switch assembly -- there's simply no room to squeeze in a probe otherwise. To get enough room to work on it, I'll have to cut two wires. All the others were left long enough, but two were not. Between the two that are not long enough and the the rest, I suspect there was a shift change.

No magic wands, eh?

Kim N5OP
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k7pp
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« Reply #48 on: October 11, 2013, 01:39:44 AM »

Hi Kim;
I'll have some shop time this Saturday.  If at all possible I'll look at my 170 and see if I can get some pix.

How about taking a chance and seeing what the sweep shows at the last stage.
Inject the signal at pin 1 of V7 and see if you can get a trace that appears to be the same amplitude on either side band and see if the symmetry follows the 1, 2 and 3 khz positions.  If it looks normal,  move up a stage for the same test,  etc.
If It doesn't buy you anything and you're not in a great hurry, I'll try to post some pix Sat evening.

Pete
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MikeKE0ZUinkcmo
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« Reply #49 on: October 11, 2013, 07:18:58 AM »

I realize the last pic you show looks pretty radical, and, the response is certainly not as it should be, but its not as bad as it seems.   Your scope is displaying a "linear" response, while the illustrations in the service manual show a logarithmic response.   The two scales are very different.   Actually there is only a 6db difference between the highest and lowest amplitudes at the pass band edges, not as earth shattering as it appears.  Linear images on your scope can show a voltage ratio of about 10:1 at best, while the illustrations in the manual, though somewhat idealized, show a voltage ratio of 10,000:1, certainly not the same scale.   Using a simple LOG detector, you can easily compare apples to apples, because the images will be on the same scale.



Here is the schematic, and pic of a LOG detector.   The IC is about $7, and you can use a standard 10X scope probe for the input test lead hooked to the radio's detector output or any of the IF Amp grids.  Here is the data sheet for the IC.





Although the pic here is of an SX-101 I.F., the overall results would be similar for most receivers. The pic here shows a 1,000:1 or 60db voltage ratio.

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