Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
HQ-170 Alignment




 
The AM Forum
October 17, 2019, 04:44:23 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: 1 2 [3]   Go Down
  Print  
Author Topic: HQ-170 Alignment  (Read 300958 times)
0 Members and 2 Guests are viewing this topic.
n5op
Member

Offline Offline

Posts: 51


« Reply #50 on: October 11, 2013, 12:00:25 PM »

You're right, Mike! I thought about that as I looked a the responses and did some log comparisons in my head. Something along the lines of "I'm looking at voltage, so dB is 20 time the log of the ratio..." and still didn't like what I saw. There's 6 dB difference between the USB and LSB setting and they are decidedly asymmetric. Those things alone are enough to force me (kicking and screaming, I assure you) to start diving in.

I need to look into building such a log prescaler for the probe.

I think, though, that I will start looking at each stage independently -- I may find that a particular stage is acting up. However, there are three stages and I might have more than one problem. If two stages have problems, then the good stage is the one that will look "different." I have to remember that this is, after all, a labor of love. If someone had to pay for this, well, it would probably never get done.

Kim N5OP
Logged
MikeKE0ZUinkcmo
Member

Offline Offline

Posts: 362



« Reply #51 on: October 11, 2013, 01:40:33 PM »

You know, when I first dive into these types of projects they wind up, at least for me, being considerably easier than I first imagined.  Not that I wanna do it again real soon. Grin

I believe you said earlier you ordered some caps.   You might also get some resistors in case some of those are out of spec as well.  I presume there are two sets of caps/resistors per stage, one for upper and one for lower, and if such is the case, you should separate your caps and resistors into "matched pairs" for each stage, even though the "sets" won't be exactly the same for each stage, your asymmetry will be better than what you have now.   The net result will be that each BW will probably have "softer" corners.
Logged

Mike KE0ZU

Bold Text and PICS are usually links

https://mikeharrison.smugmug.com/
n5op
Member

Offline Offline

Posts: 51


« Reply #52 on: October 11, 2013, 03:53:56 PM »

Thanks, Mike! Since this receiver and I go back a long way, I plan to keep it around for a long time and treat it well. I was thinking the same thing. They are all composition resistors and metal film is a better bet. I think I have enough resistors on hand, but if not they're
easy to get. I'll see if I can find someone with a capacitor checker so that I can match them up. I doubt that Hammarlund (or any of the other manufacturers) worried much about hand matching such components for the civilian market. They may have done it for some military applications and they may really have tested everything that went into even these stages.

At this point, what I really wish I had were HC6U crystals for 60 kHz, 455 kHz and 3035 kHz as that would make aligning this receiver much easier. Unfortunately, such crystals are rather difficult to find anymore; I've certainly had very little luck.

Kim N5OP
Logged
MikeKE0ZUinkcmo
Member

Offline Offline

Posts: 362



« Reply #53 on: October 11, 2013, 06:28:47 PM »

They call out DM-15 silver micas.   Could be wrong but I believe those are 5%.  In any event the ones in the radio probably will have the tolerance stamped on them.
Logged

Mike KE0ZU

Bold Text and PICS are usually links

https://mikeharrison.smugmug.com/
n5op
Member

Offline Offline

Posts: 51


« Reply #54 on: October 12, 2013, 02:10:23 AM »

The silver micas I could see said either 2% or had an actual capacitance tolerance, as in "+/- 2 pF." I also looked at the switched resistors. While nearly all are in spec (based on the tolerance markings), nearly all on on the high side, which is what I'd expect with carbon compositions resistors.

I did some stage-by-stage testing today. There are three IF stages and two IF amplifiers. The first stage is right off the 3rd mixer, the second stage comes after the 1st IF amp and the third stage after the second IF amp. So, I injected the signal at the control grid of the second IF amp, showing me the response of the last IF stage. Perfectly symmetrical with the proper shift between sidebands. Injecting the sweep at the control grid of the 1st IF amp, I saw the sidebands move as they should, but a bit of asymmetry in the amplitude between USB and LSB (USB was lower). The asymmetry gets worse when I inject the sweep at the 3rd mixer. Were I looking at this on a log scale, the defects I see would be much less evident.

I've been reading about silver mica failures and, except for a particular kind in IF cans, failures are very rare. The failure mode is almost always very characteristic ("thunderstorm static" as the unit warms up), and I see no inkling whatsoever of that. The silver micas in this receiver are brown epoxy-dipped units. I'm becoming convinced that there's a very high likelihood that the silver mica capacitors are absolutely fine. If anything, I should be more suspicious of the carbon comp resistors and replace them first with all 5% ceramic units, re-test and decide from there.

What I'm seeing and have so carefully documented may be much the way the receiver really was the day it arrived in my dad's shack in 1959. 

Kim N5OP
Logged
MikeKE0ZUinkcmo
Member

Offline Offline

Posts: 362



« Reply #55 on: October 12, 2013, 08:31:16 AM »

Kim,

Excellent work.  This is very interesting, and your last statement may well prove to be the most logical conclusion.   When you move the injection point from stage to stage, are you moving the scope along as well, so you were only looking at single stage responses?

And, if you were looking at the individual stages, did you attempt to alter their response by adjusting the inductors?
Logged

Mike KE0ZU

Bold Text and PICS are usually links

https://mikeharrison.smugmug.com/
n5op
Member

Offline Offline

Posts: 51


« Reply #56 on: October 12, 2013, 01:18:38 PM »

No, I didn't look at single-stage response because I don't have a detector probe. The only single stage I could look at was the last one: I could inject the signal at the 2nd IF amp and see what only the last transformer response looked like. I did try hanging a 1N34A diode off of the output of the transformer (essentially the control grid of the next IF amp) but that didn't work. It acted as if the stage became very heavily loaded and I could see nothing on the scope.

I then injected the signal into the second stage, but I then could see only the combination of the second and third stages and not the second stage in isolation.

I've looked at what the switching does. Obviously, it switches capacitors that step the IF passband to one side or the other. Switching also changes the screen voltage of the 6BA6 amplifiers. Switching the screen voltage must address the different gain needed at different bandwidths. It also looks like the bias is changed, too. Looking at the capacitors, it's evident that these are used to not only step the passband to one side or the other, but also appear to stagger tune the stages. Resistors are also placed in series with the switched capacitors, which must address the Q of the individual stages and so broadens the response. 

I didn't attempt to alter the response by adjusting the slugs. I'd tried something a bit similar earlier, but while looking at the entire IF response at the 6 kHz bandwidth (3 kHz selectivity and "both" sidebands. If you saw that post it said that I could get a pretty good looking 6 kHz response at the cost of an utterly deaf receiver at the narrower bandwidths.

I do not suspect the capacitors in the "cans" because each and every transformer shows a very marked peak as I adjust it. If those capacitors were bad/open/shorted, adjustments would make no difference.

Kim N5OP
Logged
n5op
Member

Offline Offline

Posts: 51


« Reply #57 on: October 12, 2013, 11:52:53 PM »

Pete, K7PP, was kind enough to haul his HQ-170 out of its exalted spot on his operating desk and into his work shop. There, he swept the 60 kHz IF just as I had. And, Lo! and Behold! His looks just like mine.

I have come to the conclusion that there's no trouble to shoot in my receiver. The reason I thought there might be problems was multifaceted. First, I was bolstered by theory but forgot a fundamental maxim: "In theory, there is no difference between theory and practice. But in practice, there is." I know exactly what the ideal should look and act like. I've nearly accomplished that with my TS-930S and I expect no less from my Orion II; because it's all done in software, I can make it look pretty much any way I want. I worked diligently to make my TS-930S as near perfect as possible. I expected to be able to get pretty close with my HQ-170. And, in fact, I got closer than I'd initially thought.

Had I displayed the passband response on a log scale, instead of a linear one, I would have seen that it was flat to within about 1 dB. I certainly would have seen some asymmetry, but it wouldn't have looked as bad. I know because I took actual readings and then plotted them on a log scale and it sure looks a lot flatter that way. So, Mike, KE0ZU, was onto something significant in that alone.

I was surprised to see 3 dB difference between the USB and LSB selection, but forgot that this is a hot receiver with gain to spare. In practice, I'd never notice the 3 dB difference. Obviously, I hadn't noticed it during operation: I only became aware of it when compared to the ideal.

I then failed to temper my expectations with a dose of reality. In truth, I'd never delved this deeply into the alignment before, nor had I read of any details from anyone else who had. I mislead myself based on what I saw depicted in the manual, which was on a log scale.

In the process, though, I learned a helluva lot about this receiver. I actually measured some resistor values and learned that, because it has always been kept in a controlled environment, the resistors that are used in the 60 kHz IF chain are all still all within their tolerance specification. Some research showed that I needn't worry about the silver mica capacitors in this receiver: the type that are used in the IF chain bandpass and sideband selection simply don't go bad unless they're damaged physically or subjected to too much voltage. I checked all the tubes and found them all fine (I have a Weston 981 tester; it says it's a Type 2, but because of some mid-type production changes it's nearly a Type 3). I learned that I suffer no evidence at all of failures of the capacitors in the IF cans. Overall, I learned that this old beast is in remarkably good shape. As Jim, W5JO, quipped, I've been given a tremendous head start with this gear because my Dad kept it in good shape and well protected for many, many years before I got it.

So, with all of Pete's expertise and experience to reassure me, and Mike's note that I'm not looking at the response in the way it's usually depicted, I have decided that the performance I'm seeing is probably very representative of the way it was the day my Dad put it into service in his shack back in 1959. So, I'm going to button it up and put it back where it belongs: next to the Globe Champ 350 that has been its constant companion since the day it was unpacked.

Then I'm gonna enjoy some radio time.

Kim N5OP
Logged
n5op
Member

Offline Offline

Posts: 51


« Reply #58 on: October 13, 2013, 04:04:35 PM »

One other note I feel I should add: having done all of this on my Hq-170, I learned a bot more abpout operating it. The LSB is a bit narrower than the USB -- that's the way it is. But, as I fiddled with it, I began to learn about some of its flexibility that isn't explicitly mentioned in the manual. In fact, the manual says to change the BFO setting only for the purposes of adjusting CW pitch. Maybe what I learned it was common knowledge in the day, but I've never heard anyone discuss it. 

In particular, on SSB it is possible to emulate, though not completely duplicate, variable passband tuning (PBT). I can move the location of the received passband by offsetting the BFO. On LSB, if I offset the BFO down in frequency (and re-tune for intelligibility, of course), I can move the passband into the upper frequencies of the transmitted signal. If I move it up in frequency, I move the passband into the lower frequencies of the transmitted signal; vice versa for USB.

Since my Globe Champ 350 doesn't do SSB, I'll probably not use this very much on a routine basis, but it might come in handy if I have QRM troubles on AM and decide I can alleviate some of it by  receiving only one of the sidebands.

Kim N5OP
Logged
k7pp
Member

Offline Offline

Posts: 62


« Reply #59 on: October 13, 2013, 06:27:12 PM »

Kim,  other than what you just mentioned,  I've found my Hammarlunds are a real joy on AM mode as well.  If you have ever been on the "AM" frequencies on 75 or 160,  you may hear background QSO's going on in other parts of the country and not strong enough to cause a local QSO a problem but strong enough to be an irritant.   Many are not "netted" to the exact frequency and a beat note can plainly be heard.  Try moving the notch filter to the beat note and you may be surprised at the suppression you can achieve.   Also,  you can switch sideband filters with the BFO off.  Sometimes a great QRM fighter if you have SSB above or below you.
Lastly,  the Hammarlund "A" series has a separate "SSB" position where the BFO control has no effect.   You can still switch to CW and do the same thing with the SSB in the upper or lower position.
Pretty slick for an old boat anchor.

Got my 170 put back together with new dial light bulbs so we're already to go back in service.  Just starting an installation of a crystal calibrator in the old 129-X.   Should be a real help finding the band edges.

Pete
Logged
n5op
Member

Offline Offline

Posts: 51


« Reply #60 on: October 13, 2013, 08:04:35 PM »

I haven't needed the notch, yet, but I know that is deep enough to completely eliminate the calibrator signal! As for using USB and LSB without the BFO, I know it's possible, I've simply not needed it, yet. I have used the sideband mode in a few AM QSOs to dodge QRM. It almost always helps.

Thanks again for all your help and efforts, Pete!

73!

Kim N5OP
Logged
Pages: 1 2 [3]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.038 seconds with 18 queries.