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Old 8th Jan 2020, 5:23 pm   #21
Skywave
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Arrow Re: Hammarlund HQ-180A I.F. Help Sought

"A resistance between D and E of 2.4 Ohms, as originally stated: that could be a problem".

Yes, that most certainly won't be correct. The leading Q., of course, is, "Why?"

► What follows can be most readily be understood by looking at my circuit sketch which is appended to post 17 (q.v.)

What immediately springs to mind is that 9 pF top coupling capacitor, (C153 I believe). Up to now, I don't think that item has been checked. Difficult to see how that 2.4 Ω resistance reading could arise by any other means - apart from a partial internal s/c between the pri. and sec. - which we can rule out, since the resistance between c and d of T3 was measured and found to be very high. Not only are the separate resistances of the pri. and the sec. of T3 greater that 2.4 Ω, but the total combined series resistance of the pri. and sec. of T3 is greater than 2.4 Ω, too. So that rules out anything on a and c. That leaves pins d and e - across which that 9 pF sits. From d, there is the 3 pF (C16) to the grid of V4; from e, the feed to V3 anode / plate. Hence, difficult to see how anything on pins d and e could be the cause . . . except for that 9 pF / C153 . . . which takes me back to where I came in.

Al.

Last edited by Skywave; 8th Jan 2020 at 5:34 pm.
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Old 8th Jan 2020, 7:00 pm   #22
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Default Re: Hammarlund HQ-180A I.F. Help Sought

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Originally Posted by IsquaredR View Post
I rechecked the resistances with both a 20000 ohm/volt Simpson 260 and an HP 410B VTVM and A to D read 8.4 ohms, C to E read 9.2 ohms and C to D was infinity.
That suggests the transformer is ok, if those measurements were taken with C153 in circuit with the transformer that would also suggest that C153 is ok as well....

….So far as I can make out the middle tag with the two red wires is just an anchor tag that's probably supplying the 250 volts to the anodes of the RF amp and the 1st mixer etc.

Once again I'll say that the anode voltages for V12 and V3 given in the manual in the link in Post#5 are wrong according to the schematic, according to the schematic the only way they can be 250 volts is if the OA2 stabilizer hasn't struck.

Lawrence.
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Old 8th Jan 2020, 7:15 pm   #23
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Default Re: Hammarlund HQ-180A I.F. Help Sought

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Originally Posted by IsquaredR View Post
I re-checked the resistances with both a 20,000 ohm/volt Simpson 260 and an HP 410B VTVM. A to D read 8.4 ohms, C to E read 9.2 ohms and C to D was infinity.
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That suggests the transformer is ok. If those measurements were taken with C153 in circuit with the transformer, that would also suggest that C153 is ok as well....
Indeed: the really critical bit being the "If" of "If those measurements were taken with C153 in-circuit with the transformer".
And if they were - and the measurements are correct and reliable - what else is there left to produce that low resistance reading across e and d?

Al.

Last edited by Skywave; 8th Jan 2020 at 7:23 pm.
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Old 8th Jan 2020, 7:30 pm   #24
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Default Re: Hammarlund HQ-180A I.F. Help Sought

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Quote:
Originally Posted by IsquaredR View Post
I re-checked the resistances with both a 20,000 ohm/volt Simpson 260 and an HP 410B VTVM. A to D read 8.4 ohms, C to E read 9.2 ohms and C to D was infinity.
Quote:
Originally Posted by ms660 View Post
That suggests the transformer is ok. If those measurements were taken with C153 in circuit with the transformer, that would also suggest that C153 is ok as well....
Indeed: the really critical bit being the "If" of "If those measurements were taken with C153 in-circuit with the transformer".
And if they were - and the measurements are correct and reliable - what else is there left to produce that low resistance reading across e and d?

Al.
Nothing according to the schematic I'm looking at.....

There's no low resistance reading between primary and secondary according to the OP's last measurements because he said that there was infinity between C and D.....

Lawrence.
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Old 9th Jan 2020, 1:52 am   #25
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Arrow Re: Hammarlund HQ-180A I.F. Help Sought

Yes, in his post # 11, he did state that. However, in his earlier post # 3, he stated D to E = 2.4 Ω. Although in post #11, he subsequently amended some of his measurements of those in post #3, the resistance measurement, D to E, had not been revised. Hence, my conclusion was based on that earlier - and unrevised - measurement.

But let's assess where we are now: a summary, based on my understandings . . .
R12 was shown as going to T4. We now know that to be incorrect: it should be shown as going to the OA2 valve (via the RX / TX switch), thus supplying stabilized +150 v. to V17 / plate and V3 / plate. That much from the schematic drawing, which not only makes sense, but partly explains the strange voltages the OP initially found at those two points. Now add in the error in the manual (which you found), and that completes the reason for those strange voltage readings.
Seems to me that once T3 is re-fitted and R12 is correctly electrically installed, then a power-up and test of this radio - including that the voltages on V17 and V3 are now O.K. - will be worthwhile.

But let's not 'jump the gun' on this, but now wait and see what IsquaredR thinks . . . . so far . . . .

AL.
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Old 9th Jan 2020, 3:36 am   #26
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Default Re: Hammarlund HQ-180A I.F. Help Sought

Lawrence, Al and Don...I've got a big fat problem and I am going to destroy any credibility I might have had when I tell you about it. I mistakenly labeled (on my drawing) the transformer to which the 1 K ohm resistor was connected from T3's Pin "C" as T4. It is not T4. It is T5 and I regret all the head-scratching I have caused you good people. However even after admitting my boneheaded error, I do not see why or how there is any 1 K ohm resistor going between T3 (pin "C") and any pin on transformer T5; nowhere surrounding T5 do I see a 1 K ohm resistor. So something is still awry.

By the way, my resistance measurements were taken with that 9 pF capacitor in place. Also, I remeasured the "D" to "E" resistance with the original device (a DVM) and it was infinity so I don't know how I first got the 2.4 ohms reading. Maybe my finger was touching the probe or something like that. Or werewolves? Or maybe those IF Can Skyscrapers that Al was dreaming about last night were causing the ether to be more conductive and 2.4 ohms was the resistance of the air space between "D" and "E." Actually and probably more logically it was a measurement of the dead air space between my ears.

Anyway, I am coming around to being a full supporter of Lawrence's THEMANUALISWRONG theory. The technical writer for the Hammarlund manual just wasn't paying attention I guess. You guys have made a believer in me that what I should see on the anodes of V17 and V3 is what I am getting, around the OA2 voltage of 140 volts. So I am going to button the IF can back up, reinstall it, remeasure volts and see what I've got. Somewhere I am losing signal through that IF chain and will report back here once it's back together and I have stopped banging my head against the wall.
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Old 9th Jan 2020, 11:38 am   #27
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Default Re: Hammarlund HQ-180A I.F. Help Sought

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Lawrence, Al and Don...I've got a big fat problem and I am going to destroy any credibility I might have had when I tell you about it. I mistakenly labeled (on my drawing) the transformer to which the 1 K ohm resistor was connected from T3's Pin "C" as T4. It is not T4. It is T5 and I regret all the head-scratching I have caused you good people. However even after admitting my boneheaded error, I do not see why or how there is any 1 K ohm resistor going between T3 (pin "C") and any pin on transformer T5; nowhere surrounding T5 do I see a 1 K ohm resistor. So something is still awry.

By the way, my resistance measurements were taken with that 9 pF capacitor in place. Also, I remeasured the "D" to "E" resistance with the original device (a DVM) and it was infinity so I don't know how I first got the 2.4 ohms reading. Maybe my finger was touching the probe or something like that. Or werewolves? Or maybe those IF Can Skyscrapers that Al was dreaming about last night were causing the ether to be more conductive and 2.4 ohms was the resistance of the air space between "D" and "E." Actually and probably more logically it was a measurement of the dead air space between my ears.

Anyway, I am coming around to being a full supporter of Lawrence's THEMANUALISWRONG theory. The technical writer for the Hammarlund manual just wasn't paying attention I guess. You guys have made a believer in me that what I should see on the anodes of V17 and V3 is what I am getting, around the OA2 voltage of 140 volts. So I am going to button the IF can back up, reinstall it, remeasure volts and see what I've got. Somewhere I am losing signal through that IF chain and will report back here once it's back together and I have stopped banging my head against the wall.
No problem, the voltage error in the manual was one of the first things I spotted.

The tag on T5 that the 1k is connected to could just be another anchor tag, the windings of T5 should have no connection to any HT source.

Never used a HQ180 but I used to own a HQ150 which was a good performer.

Lawrence.
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Old 10th Jan 2020, 2:41 am   #28
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Arrow Re: Hammarlund HQ-180A I.F. Help Sought

IsquaredR: "Somewhere I am losing signal through that IF chain and will report back here once it's back together and I have stopped banging my head against the wall".

Once you've powered this RX up, the first thing I would do is check the voltages on the electrodes of all the valves in the I.F. chain. Yes, use the manual as a reference, sure, but as we have discovered, sometimes tech. manuals have mistakes in them, so when measuring / checking, I always ask myself "I have xx volts at this point: does that make sense?" - And then act accordingly.

Once happy with that, the next I would do is use my trusty sig. gen. & 'scope and trace the signal through the entire I.F. chain, valve-by-valve, again asking myself that same Q. as above.

When tackling difficult faults like this, it's always worthwhile keeping a few thoughts in your head so that you can keep a grip on the ol' sanity:
1. This item used to work - once upon a time - so it can be made to 'work' again.
2. There may be more than one fault - but there won't be an infinite quantity of them!
3. Patience, persistence and perseverance: you can never have too much of any of them. They're 'tools' that are under our control - and they're free.
4. If in doubt, ask - as you have been doing. Don't let your ego or pride hamper you.
5. Never forget the tools Mother Nature gave you: these are also free. Sight, sense of touch, hearing and even smell. (Yikes! Where's that smoke coming from! And I can smell it - and this resistor feels really hot! And "OMG! What **** was that bang?" )
6. And finally time: obviously linked to 3 above. Don't rush the job. Some faults take a lot longer to clear than is often anticipated prior to starting 'the fun'!

Al.
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Old 10th Jan 2020, 4:06 am   #29
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Default Re: Hammarlund HQ-180A I.F. Help Sought

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IsquaredR: "Somewhere I am losing signal through that IF chain and will report back here once it's back together and I have stopped banging my head against the wall".

Once you've powered this RX up, the first thing I would do is check the voltages on the electrodes of all the valves in the I.F. chain. Yes, use the manual as a reference, sure, but as we have discovered, sometimes tech. manuals have mistakes in them, so when measuring / checking, I always ask myself "I have xx volts at this point: does that make sense?" - And then act accordingly.

Once happy with that, the next I would do is use my trusty sig. gen. & 'scope and trace the signal through the entire I.F. chain, valve-by-valve, again asking myself that same Q. as above.

When tackling difficult faults like this, it's always worthwhile keeping a few thoughts in your head so that you can keep a grip on the ol' sanity:
1. This item used to work - once upon a time - so it can be made to 'work' again.
2. There may be more than one fault - but there won't be an infinite quantity of them!
3. Patience, persistence and perseverance: you can never have too much of any of them. They're 'tools' that are under our control - and they're free.
4. If in doubt, ask - as you have been doing. Don't let your ego or pride hamper you.
5. Never forget the tools Mother Nature gave you: these are also free. Sight, sense of touch, hearing and even smell. (Yikes! Where's that smoke coming from! And I can smell it - and this resistor feels really hot! And "OMG! What **** was that bang?" )
6. And finally time: obviously linked to 3 above. Don't rush the job. Some faults take a lot longer to clear than is often anticipated prior to starting 'the fun'!

Al.
Thank you Al. No truer words were ever spoken. I made progress tonight and, indeed (as you stated) " There may be more than one fault - but there won't be an infinite quantity of them!" I also traced the signal through the whole IF chain and found two problems. First was a poor connection on the T4 coil (apparently I didn't scrape away enough of the IF coil wire's varnish when I soldered it after adding its new LC capacitor). Then I proceeded down the line checking inputs and outputs of each grid to anode until I got to T10 and T11 which is where I am now. The signal that flowed so nicely (and most importantly responded to transformer adjustment) dies at the input to T10. I've already stripped naked T10 and T11 and believe no issues are in those coils. There is lots of signal coming from the anode of V7; none reaching the grid of V8 however. I also measured a very high anode voltage (290 VDC) on V7 suggesting that it is not loaded.So that's my focus now. But I feel like I am getting closer. There's no audio from the speaker and all my signal tracing has been via my signal tracer. I have a feeling that when I find the cause it will open up the floodgates and send thousands of gallons of audio to the 1st audio and output stages.

You know what, Al? I'm enjoying this "dance." Sure this is a vintage receiver and I could toss it out in the street, buy something else and forget about it. But then I'd miss this experience and the challenges are something I am enjoying. Once it is working it will be that much more satisfying to me because I'll feel part of me remains in that receiver. I wouldn't get that feeling just going out and buying a Whizzbang 2000 Mark IV and plugging it in.

I sure appreciate you and the other gentlemen who have been with me on this ride. This is a wonderful group.
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Old 10th Jan 2020, 3:11 pm   #30
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Arrow Re: Hammarlund HQ-180A I.F. Help Sought

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I'm enjoying this "dance." Sure this is a vintage receiver and I could toss it out in the street, buy something else and forget about it. But then I'd miss this experience and the challenges are something I am enjoying. Once it is working it will be that much more satisfying to me because I'll feel part of me remains in that receiver.

"I'm enjoying this 'dance'." An apt choice of metaphor & I'm with you on that. For myself, I enjoy solving puzzles, be that almost any type: crosswords & maths., especially. For some people, their brains are just 'hard-wired' that way. They are often the type of people that make competent and skilled engineers. (Not that I make any particular claims in either category).

If you were to give up on something like this, it would leave a bitter memory that would haunt you for the rest of your life: really, really not nice.

"Part of me that remains in this RX". The attitude that is brought to bear in doing tasks like this is not limited to repairing radio / electronics items: it extends to many other things. When I cast my mind back to the various houses I have bought, lived in and made changes to - be those essential or mere improvements in details - I cannot forget what I did: a chunk of me remains in those houses, a 'chunk' consisting of blood, sweat, tears - and often quite a lot of 'midnight oil', too!
A famous man once said: 'Creativity is 5% inspiration and 95% perspiration"

Al.
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Old 11th Jan 2020, 4:57 am   #31
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Default Re: Hammarlund HQ-180A I.F. Help Sought

My Hammarlund dilemma is no more.

But first a comment to Skywave: Your last posting was poetic and profound. In fact I printed it out to save in a file I keep of such things. I should copy it on a slip of paper and pass them out to every newbie ham and a whole lot of guys who have been around a long time but have forgotten what drew them into the avocation in the first place.

Now to the Hammarlund. There's a lesson here but I am sure I didn't learn it (been fooling around with ham and shortwave radio for a lot of years so my patterns are probably pretty well set and I'll probably do other similarly stupid things...and continue to do them till my ashes become part of the Earth and every valve radio will breathe a sigh of relief).

So, I caused both problems rendering the HQ-180A mute. The first was simply carelessly not scraping the varnish off one of the IF coil wires when I soldered a new resonance capacitor in the can. Readers of this thread may recall I then was able to trace an injected signal all the way through the IF chain until I got to the two last IF cans which had zero signal for driving the final 60 KC IF amplifier/AVC/Detector. This was a puzzler because I had beaucoup signal coming out of the plate of V7 and going into the two IF cans, T10 and T11. And there was NOTHING really connected to this part of the circuit except a worm's nest-like wire bundle that took the signal to several wafers on a multi-gang switch and back again to end up at V8. With a doubtful and, by now, a cynical attitude, I decided to loosen the double control assembly consisting of multiple gangs used to select bandpass width and sidebands. Beneath its nightmarish Rube Goldberg assembly I discovered a bare wire going from one of the pins on IF transformer T11 to the input of V8. Apparently when I installed a new resonance capacitor in that can and it was time to re-secure it to the chassis, I used the blade of a screwdriver to lock down the locking yoke of the can. Those who have done this will recognize the process and know it makes a comforting "click" sound when the can is resecured. Well, evidently between my screwdriver blade and the can's locking yoke was sandwiched the bare wire that feeds V8 and the act of my locking it down also securely pressed the rigid bare wire against the metal locking yoke which grounded everything coming from the transformer. When I locked the can in place I heard the "click" but couldn't actually see the underside and the newly grounded bare wire because it was hidden by the dual-control assembly.

So tomorrow I am looking forward to a nice session aligning her but based on the cursory adjustments made in the process of troubleshooting I already like what I hear coming from the speaker.

That's the story and I want to thank every one of you gentlemen for your help, diagnostics, hypothesizing, wisdom, patience and courtesy. You make this a wonderful forum.
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Old 11th Jan 2020, 1:45 pm   #32
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Arrow Re: Hammarlund HQ-180A I.F. Help Sought

IsquaredR: the second paragraph in your post above requires a response by me (not doing so would be rude).

I am flattered by your comments therein - thank you.
I like to think that my motivations were purely altruistic, motivated by simple memories of "been there; done that; got the T-shirt". Also, I recognise that I am not the only member here who has been of assistance to you.

As regards my membership of this forum, I am here to learn as much as I am here to contribute.

"My Hammarlund dilemma is no more." That, of course, is good news. However, I don't want to rain on your parade: you still have the alignment check / adjustment to do. Yes, things look promising, but you ain't quite there yet. Best of luck: keep us posted when the checkered flag finally gets waved.

TTFN
Al.
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Old 13th Jan 2020, 12:13 am   #33
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Default Re: Hammarlund HQ-180A I.F. Help Sought

Warm greetings Al and others from whom I received such helpful suggestions.
I am happy to report that I did the stock-in-trade factory-recommended alignment of the HQ-180A and it turned out beautifully. I have not yet done a sweep alignment and, frankly I am hesitant to do one because it sounds good now and I doubt I can improve on it but more likely would probably goof it up ("if it's not broke..."). In fact, just for laughs after I finished the factory-recommended alignment I connected my sweep generator to check the filter response on each sideband as well as both sidebands. I am attaching the oscilloscope pattern of both sidebands. (Each sideband's pattern was nearly identical only positioned slightly left to to the right of the 60 KC center frequency). For all the trouble it caused me (and all the perplexity caused the good people of this forum), it was worth it.

You guys are terrific. Thanks.
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Old 13th Jan 2020, 2:29 am   #34
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Hi!
It's good to hear that you have finally restored your HQ180 to full health. But looking at your picture of the display, I'm a bit puzzled: I don't think I fully understand what I am looking at. I'll explain . . .

Am I correct in thinking that the 'flat top' of that display is the 60 kHz pass-band and that the sloping parts of that display - on either side of that flat top - are the skirt responses of the 60 kHz filter? If I am, then surely those two skirt responses should look the same, i.e. a symmetrical response, no?

And secondly - just out of interest - what is make & model of the sweeping sig. gen. that you are using?

Al.
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Old 14th Jan 2020, 12:08 am   #35
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Default Re: Hammarlund HQ-180A I.F. Help Sought

Hi Al,

Yes, that is the 60 KC response "right out of the box." I haven't adjusted anything and the trace is whatever came from the factory manuals alignment procedure in which the IFs are just "peaked." My sweep generator is a Hewlett Packard 8601A. Still not sure if I want to mess with the IFs again by doing a sweep alignment and potentially screw up the passband performance that I now have.

I'm in the process of doing some other "housekeeping" with my HQ-180A like adding an octal socket inside so I can either use the clock or not use the clock. I'm also adding inrush protection. The clock is something I never use and I find it annoying because of its mechanical noise. I want to be able to conveniently remove an octal type jumper plug and plug in the clock if I (or anyone else who ever owns this receiver) wants the clock working. I'm also adding an inrush thermistor which will hopefully take care of the "THUMP" of the poor ol' transformer when the receiver is turned on. Also I don't need the filaments warm all the time either (when the Hammarlund is plugged in the filaments are powered and that's too much vulnerabilty as a potential fire hazard for my peace of mind) so I might do some slight changes in that part of the circuit to depower the filaments when the set it turned off.

I've also got the crystal assembly from a Hammarlund HQ-180AX that I parted out some years ago and am trying to either talk myself out of...or decide to proceed with...removing the clock entirely and installing the crystal assembly, thus turning my HQ-180AC into an HQ-180AX.

So as you can see this HQ-180A is more of a "career" than a project.
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Old 19th Jan 2020, 11:35 am   #36
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Default Re: Hammarlund HQ-180A I.F. Help Sought

For what it's worth, I overhauled my HQ170 a few months back.
I included a drawing of the tools I had to make for the transformers.
http://www.radiomuseum.co.uk/HQ170%20restoration.html
Top band sensitivity wasn't very good but I moved on to something else before sorting that out.
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Old 21st Jan 2020, 3:46 pm   #37
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Default Re: Hammarlund HQ-180A I.F. Help Sought

Allan, that is an amazing page you put together for the HQ-170. I would love to find something like that based on the HQ-180A; regardless, I copied your page as much of the information can be applied to the HQ-180A. Some day I may own an HQ-170 and your information will be appreciated greatly.

I am experiencing an annoying anomaly that I just cannot seem to find in my HQ-180A. I have done so many things trying to clear it up without success. On the two top bands (7850 to 15350 and 15350 to 30 MC) when I tune in a station it sounds like the signal is popping in and out of the receiver pass band filter. On the lower 3 bands, as I tune in a station there is a very nice slow increase, peak and decrease in the amplitude and fullness of the signals. But on the top two bands it tunes very oddly, usually requiring that I "rock" the main tuning dial to get a signal...then it's at full strength...but often disappears if I have rotated the main tuning knob a hair's width too far.

I've done everything to try to solve this problem that I can think of. I even removed the MAIN TUNING and BANDSPREAD tuning condensors, soaked them in naphtha to remove old dried grease, relubricated them and installed them. The IF can resonant capacitors have all been replaced. Huge undertaking to put it mildly! It aligns nicely using the factory peaking procedure and sounds beautiful on the lower three bands. But from 7850 to 30 MC it is troublesome.
Perhaps one of the crystals is not resonant at the right frequency. Don't know and am weary thinking about it. If anyone has any ideas I would be grateful if you'd share them. Thanks.
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Old 23rd Jan 2020, 3:26 pm   #38
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Default Re: Hammarlund HQ-180A I.F. Help Sought

That latest problem sounds really horrible.
I wonder if the AVC voltage is responsible for moving an oscillator?
Is the fault present with AVC off?
I guess a basic check to see if the correct valves are in position so that there isn't a variable mu valve where there shouldn't be and vice versa. Check the three 6BE6 valves are correct and not the wrong type. If the valves are correct try swapping the 6BE6s around in case one is faulty, then try a different 6C4.
Try a signal generator whilst monitoring the AVC line, or if this is OFF, monitor the HT line and see if the pulling is absent with a few microvolts and gets bad when injecting 10 millivolts etc.
That 0A2 regulator feeds the 6C4 plus some screen grids. If the screen grids are drawing too much current on strong signals the 6C4 HT supply may move around. Try another 0A2 and/or check its 2K 10W resistor.

I have had a similar problem when using a WW2 communications receiver as a second IF for a 2 meter converter when the local oscillator was pulling on strong signals... I guess the HT voltage was changing slightly and shifting the local oscillator. I swapped the EC52 local oscillator valve for a FET and the problem went away. It was probably a basic design fault.
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Old 26th Jan 2020, 3:09 pm   #39
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Default Re: Hammarlund HQ-180A I.F. Help Sought

Thank you Allan. Have you ever got so deep in a restoration project that you aren't even sure what you've done? This is the case with this HQ-180A. I've been tweaking and re-tweaking the IF chains and apparently I must have stumbled on the correct peak because the aforementioned problem in which it sounded like signals were "popping in and popping out" as I tuned across their frequency is gone. I now get a more normal rise-maximum-decrease in signal detection as I tune past a station.

HOWEVER

A new problem has arisen and I probably have caused this one myself with all my IF tweaking. I cannot TRIM the second, third or fourth bands (1.05 to 2.05 MC), (2.05 to 4 MC) and (4 to 7.85 MC) respectively. I am able to adjust the oscillator for each of these bands but I can not trim the high frequency portion (2 MC, 4 MC and 7.85 MC respectively). I am receiving on these bands but the actual frequency that I am hearing is between 700 KC to 2000 KC low. For instance on the third band (2.05 to 4 MC) my signal generator trim marker at 4 MC ends up at 3350 KC on the dial and when I tune the HQ-180A up to 4 MC I am hearing amateur radio SSB transmissions where there should be none.
So I think I have something wrongly skewed in my IF chain. Oddly the lowest band (.540 to 1.05 MC) tracks correctly and can be trimmed at 1 MC. The two highest bands (above 7.85 MC) also track normally and can be trimmed at their respective high frequency ends so I am guessing my problem must not be in the 3035 IF section.
I sure welcome and thank all of you for any ideas.

Ironically I started working on this receiver in early December because I thought it would be enjoyable to listen to Christmas music from around the world and here it is late January and I am still trying to get this receiver running. Maybe next Christmas?
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Old 27th Jan 2020, 10:27 am   #40
allan
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Default Re: Hammarlund HQ-180A I.F. Help Sought

Thinking back to my 170 receiver I can think of two possibilities.
The first is getting the fixed local oscillator on the correct frequency which in the case of the 180 is xtal controlled at 2.580MHz so shouldn't be a problem.
The second possibility, and from your figures appears to be the case, is that you may have aligned the front end to the image instead of the design frequency.
On roughly the centre of any HF range if you set the sig gen to say 10uV you will hear a single decent response, but set it to say 10mV and you'll hear several signals, one of which will be twice the IF away from the strongest.
The easiest way of confirming the correct local oscillator frequency is to use a second receiver to confirm it is always 455KHz higher than the tuning dial setting or 3.035MHz higher on the two highest ranges.
My 170 uses a tunable 2nd local oscillator and this had been twiddled giving me alignment problems until I corrected it.
Without a second receiver or a frequency counter it's very easy to align the 180 correctly at the LF end of a range then flip to the image by the time you've tuned to the high end. The difference in response at say 30MHz between the correct frequency and the image, if you had a 455KHz IF would be very similar so the idea of the 3.035MHz IF was to make the image response a lot weaker, but given say 10mV of signal the image will be much the same strength as the correct frequency, especially if you have the AVC in operation. I guess you are correctly using the dust cores at the LF ends and the trimmer capacitors at the high ends.
I see the final IF is 60KHz and the BFO is centred on 455-60=395KHz. At least you are far enough away from MSF otherwise you might have heard a ticking noise if you use a long wire...
Allan G3PIY
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