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Author Topic: HQ 170 Dial Linearity  (Read 75948 times)
KD1I
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Posts: 466




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« on: August 27, 2014, 05:20:11 PM »

Dear Friends,  Around June I came into a very nice HQ 170 (not A) at a swap meet and the owner was honest enough to tell me it did not work. Upon inspection at home, I found lots of added wires showing someone started a modification they did not finish. I restored the wiring at it played well. Next the two fiducials did not line up. The left and right hand hair lines were badly off. It turned out to be worn plastic on the fulcrum of the right hand dial.
.  It was badly worn so I crafted a collar from .030 plastic sheet, cemented it on and carefully aligned it. The left and right hand hairlines now line up within a gnats patootie and I am very happy with that.

I restored the wiring mess to original and it does play well.  Now for my issue and I hope you can offer some advice. I have not yet aligned this baby BTW.

My issue is dial linearity.   I set the crystal calibrator to be exactly on WWV by listening to another receiver (my FT 2000) so that coupling the HQ170 to the FT 2000, I heard the zero beat at 10.000 MHZ.   The calibrator should be spot on at this point.

Next, I set the HQ 170 receiver for 14.000 MHZ and adjusted the left hand dial to zero at exactly 14.000 MHZ.   OK so far.   Now when I check the tracking, I find it  zeros as this;

The left column is where the calibrator should zero out and the right is where it actually does on the dial.
On 20 Meters:
14.000 – Spot on
14.100 – 14.094 or low by 5 KHZ
14.200 – 14.191 or low by 9 KHZ
14.300 – 14.292 or low by 8 KHZ

On 15 meters it is:
21.000 – 21.004 or high by 4 KHZ
21.100 – 21.100 or spot on
21.200 – 21.195 or low by 5 KHZ
21.300 – 21.291 or low by 9 KHZ
21.400 – 21.391 or low by 9 KHZ

So is there a solution for this or am I asking too much from this old gal?   Should I try an alignment next to see if that has any influence?   I'd really prefer to tackle one problem at a time of course.

Should I set it to be on at the middle of the bands and split the error across the bands?    Any thoughts?     Many Thanks and Best 73,   Jim     KD1I
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KD1I
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Posts: 466




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« Reply #1 on: August 28, 2014, 08:38:55 AM »

WOW ! No responses yet?      OK, for those who have one of these receivers, I just checked 75 Meters and the runout is from 20 KCS off to 30 KCS off.  Is this typical?    Seems a bit excessive.   So setting the left hand dial correctly on 20 meters will NOT enhance the performance on the other bands and even make it worse in some cases.   Guess I'm spoiled by modern rigs with digital readouts.   73, Jim
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AC5UP
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« Reply #2 on: August 28, 2014, 09:13:59 AM »

I didn't realize there was a deadline for a response...

Speaking in general terms for receivers of the era, yes, they were never spot-on across the dial and that's why the internal calibrator with markers every 25 kc's. You checked the dial when in doubt and utilized mental math or a sliding graticule to compensate. Think of this as part of the charm of boatankering.

As for your specific issue, an alignment could be your next step and for that I'll give you a condensed version the advice found in the depot manual for the venerable R-390A/URR (different rig, same concept):

*  Make sure the radio is working properly before attempting an alignment. You should never try to compensate for a circuit deficiency with a diddle stick. Fix the radio before you go through the process, no weak tubes.
*  Verify your test equipment is up to the task. Stable, within calibration limits, fully warmed up, and you have the proper tools.
*  Allow the receiver to warm up fully before starting. In the case of the R-390A Collins recommends 24 hours. An hour should be enough in your case, but if you should accidentally leave the radio on overnight...
*  Give yourself plenty of time, assume nothing, double check your work periodically, leave everything 'hot' while taking a break.
*  A digital camera is a useful way to document the chassis before starting and a Sharpie pen can mark trimmer condensers & such in case you grab the wrong one and need to go back.

If things do not go well at first chalk it up as a dry run / learning experience. You'll do better the next time.
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G3RZP
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« Reply #3 on: August 28, 2014, 09:29:20 AM »

I suspect that it is within what would be expected. Getting variable capacitors with 1% matching between sections is (was!) hellishly expensive, and getting even 5% matching from different capacitors of the same design pretty hard. Some receivers got around it by individually calibrating each radio, but that's expensive, too.

You may well find that setting it right at 14200 (and the middle of the other bands) reduces the total error because it will change sign as you go up or down.

In any case, you can set it right for the bit of band you want - CW or SSB.


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WB6BYU
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« Reply #4 on: August 28, 2014, 12:08:29 PM »

So the difference between any two adjacent 100kHz points is only 5kHz?  That's pretty good!
I always assumed you adjusted your calibration to the nearest marker (so you were never more than
50kHz away from the calibration point).

All we really cared about was keeping inside the band edges anyway:  that was easy to tell with the
calibrator at 14.000 MHz but more difficult at 14.350 MHz unless your calibrator had 50/25kHz markers.
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KD1I
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Posts: 466




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« Reply #5 on: August 28, 2014, 01:31:46 PM »

Sorry if I seemed to be impatient. I was surprised to get over 250 views and no replies on this topic. I know there are folks here who have a lot more experience than I on these particular boat anchors.....   and there you were.  So thanks for each reply. I really do appreciate it.
Each of you has a pearl of wisdom in your answers and UPs response should be written in stone. And it is true that twiddling should never cover for real problems...doesn't work that way. I have been in service in radio and medical electronics for 46 years now and those thoughts have served me well.
I just wanted to set up an antique station as I could never afford when I was licensed in 1963. This was just too expensive. I had an HQ129X back then and I never worried about dial accuracy. I just assumed it was correct - obviously it was not by a mile.
Setting this receiver's dial at 20 meters still means that on 75 meters it is off by 20 to 30 KHZ. That seems excessive to me...maybe it is not. But I would like to improve it if at all possible. Otherwise, it plays well. A bit drifty but so am I at my age. So I will take your advice, ensure it is correct before starting and then spend some quality evenings aligning this beauty.   Many Thanks and Very Best 73, Jim
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WB6BYU
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« Reply #6 on: August 28, 2014, 03:19:20 PM »

Quote from: KD1I

...Setting this receiver's dial at 20 meters still means that on 75 meters it is off by 20 to 30 KHZ...


I'd be very surprised if you didn't somehow have separate adjustments for each band - I'd have to
look at the schematic, but either you switch the oscillator (in which case it would have separate
calibration for each band) or you use a single oscillator mixed with crystal oscillators (so you'd
trim the crystal frequencies as needed.  It may be that one of the crystals has aged.)

Not having an HQ-170 on hand, what is the function of that unmarked knob to the right of the
right-most dial window?  Does it adjust the calibration, perhaps by shifting the dial pointer?  If so,
that is how you readjust the calibration to the 100 kHz points for whatever part of the band you
are operating in.



[edited to add:]


Now I had to go look it up.

There are separate oscillator coil/trimmer calibration adjustments for each band, as shown in Figures 9
and 10 of the Service Manual.  A full alignment would include adjusting the tuning on each band.  If the
tuning is too far off on 80m, readjust it.

Because the receiver uses double conversion on 160m and 80m, and triple conversion on 40m and higher
frequencies, if the 2.580 MHz crystal oscillator has drifted it would also cause an offset between the
80m and 20m dial markings.  That crystal is connected to the 6BE6 second converter stage and isn't
provided with a trimmer capacitor (though one could be added if needed.)  But any drift in that frequency
should be accommodated for by readjusting the oscillator tuning.

The manual also says that the expected accuracy is nominally +/- half a dial division
« Last Edit: August 28, 2014, 03:41:22 PM by WB6BYU » Logged
AA4PB
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Posts: 15050




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« Reply #7 on: August 28, 2014, 04:20:38 PM »

Not sure about the HQ170, but some of these old receivers used a coil and a trimmer capacitor for each band. You would adjust the tracking by tuning the coil for proper calibration at one end of the dial and the trimmer capacitor for proper calibration at the other end. You would alternate that process several times until both ends of the dial were as close as you could get it then the dial would track as close as possible throughout its range.

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Bob  AA4PB
Garrisonville, VA
KD1I
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Posts: 466




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« Reply #8 on: August 28, 2014, 04:29:36 PM »

Thank you, Dale. That gives me more to go on.   I will tackle the alignment starting with the 3rd IF and working forward. I do have a manual from BAMA and I'm armed with an old assortment of test gear - SG-85/URM -25D signal generator, Frequency counter of unknown accuracy and Philips PM3240 x scope...typical ham collection.
I can see the logic of the front end alignment affecting each band so there is hope yet. The rest of this works so well and is cosmetically so nice I really would like to do the best I can....    comes from 42 years of tweeking cardiovascular x-ray labs to do the very best resolution possible for their day.

Many Thanks es 73,   Jim
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AA5WG
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« Reply #9 on: August 28, 2014, 06:32:14 PM »

Jim,

Here is a youtube link on the HQ-170A by K7PP. 

K7PP has several nice youtube videos on your
very nice radio.

http://www.youtube.com/results?search_query=hammarlund+hq-170+alignment

73,
Chuck
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KD1I
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Posts: 466




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« Reply #10 on: August 28, 2014, 06:42:27 PM »

Thanks, Chuck. Those are great videos. Pete is a good guy. I have corresponded with him here and directly. He's a fountain of knowledge on these Hammerlunds.   I'm going for the full alignment after viewing the videos and reading the manual for the 5th or 6th time.   Can't be too careful.  73, Jim
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G3RZP
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« Reply #11 on: August 29, 2014, 12:54:18 AM »

Sounds like a full realignment is called for. One point to watch is the coupling capacitors that provide the switched selectivity in the 60kHz IF - if they drift, you may well have problems getting the selectivity right in all selectivity and sideband switch positions.
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KD1I
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Posts: 466




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« Reply #12 on: August 29, 2014, 03:36:08 PM »

Well, life is full of challenges and opportunities, isn't it.   In checking my two signal generators I find that one is very unstable; too much so to do a decent calibration at 60 KHZ. The other, an old military surplus unit but very nice otherwise, puts out such a distorted wave form at 60 KHZ that my counter will not count it.
However, at 455 KHZ, it is a very nice sinusoidal wave and quite stable over time.  So my idea to set up the 60 KHZ IF is to use the 455 KHZ fed to the grid of the 60KHZ mixer and let the mixer do its magic to convert it down. (just as it normally would for any signal)
With 455 KHZ into the mixer it would result in 4 frequencies out: the 455 KHZ, the 515 of the oscillator, the sum which is 970 KHZ and the difference which is 60 KHZ of course. Since the transformers are already close to 60 KHZ if not on, it would only require a small trim to optimize them and of course, they would not be resonant at any of the other frequencies. The variable is the Oscillator (converter in this case)which is adjusted by the fine tuning. If it is set to '0' on the right hand dial, all should work well.
Is my logic sound?   See any flaws in my thinking?    Many thanks and 73, Jim
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WB6BYU
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« Reply #13 on: August 29, 2014, 03:38:53 PM »

Quote from: KD1I

...I can see the logic of the front end alignment affecting each band...



No, it isn't the front end alignment.  It is the VFO alignment that also has to be done for
each individual band.  That's why it affects the VFO frequency and linearity.

So basically, on each band you adjust the L and C in the VFO to make the ends of the tuning range
line up.  Hopefully once you do that the calibration is reasonably close in the middle of the band, but
it may not be over a wide band such as 80m.  In that case, you tune in the nearest 100kHz calibrator
signal and adjust the unmarked calibration knob (which may move the dial pointer relative to the
rotating dial behind it) to get the scale to read correctly.  That should get you within 5 or 10 kHz
between calibration points.

You use the same calibration procedure as for the front end:  adjust the coil at the low end of the band
and the trimmer at the high end of the band, but in this case you are shifting the frequency to match the
dial rather than peaking the front end for maximum signal.
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KD1I
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Posts: 466




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« Reply #14 on: August 29, 2014, 03:56:44 PM »

Thanks for the reply and clarification, Dale. It was a bad choice of words on my part. I meant "front end" in an all encompassing way and of course, that is not right to do.   Yes, the VFO would do the trick and as soon as I sort out the issue that I posted on the 60 KHZ IF alignment, I'll try that.   I really planned to do this a step at a time, starting with the 60 KHZ IF and moving forward.  I have all the time because this is a nice project and a lovely radio that I plan to keep and enjoy.   Very Best, Jim
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