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Author Topic: HQ 170 Dial Linearity  (Read 75941 times)
AC5UP
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« Reply #30 on: September 01, 2014, 08:30:31 PM »

CLICK HERE for more than you'll ever want to know about the URM-25D...... I had a feeling you were using the signal generator in ways the DoD never intended and frustrating yourself in the process.

There are features like the crystal calibrator that were a mystery to me before I read the book.  The generator has an internal 25 kc calibrator with a no-tune crystal radio style detector which is infinitely more practical than a 50's vintage frequency counter.  Plug in a pair of headsets, turn on the calibrator, tune for the nearest zero beat.  Note the amount and direction of any error on the VFO dial then compensate for same at the intended frequency.  Simple, yes.  Accurate, yes.  Intuitive, no.  Without the book you're unlikely to get full value from the generator, so spend a little time learning how to set the output level and check the frequency calibration.  Your reward will be a better alignment.............  Wink
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KD1I
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« Reply #31 on: September 02, 2014, 06:20:40 AM »

Thanks, Nelson.   Great resource for the signal generator. I was able to download the first manual in just a moment.  I think the smart thing to do is to read and learn to use the generator correctly before proceeding. All these years I chided our field engineers to "know your test gear and how to use it" and then didn't do just that myself. Hubris.  Anyway, I thank you.   Maybe this will give a clue why the signal collapses when connected to the grid of a 6BE6.   I've watched Pete, K7PP's videos and noticed he uses the same generator and had no problem injecting 455 0r 3035 into the first mixer, V2, as the instructions stated.    Best 73, Jim
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WB6BYU
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« Reply #32 on: September 02, 2014, 08:12:46 PM »

You can try coupling the generator through a small capacitor.  Perhaps 10pf at HF, somewhat
larger on the lower frequencies.  That reduces the input signal strength, provides DC isolation,
and reduces loading.
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KD1I
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« Reply #33 on: September 03, 2014, 07:36:25 PM »

Well, I tried the coupling capacitor - 6.8 pF, 10 pF and 33 pF.    Did not help. I could not inject as described in the instructions for the 455 KHZ and 3035 KHZ IFs.    I tried all combinations to feed it from the generator. Nothing drove it enough to show any AGC action.  Finally, in desperation, I tried the grid of the first RF amplifier. Bingo. It worked with any small value cap.  So now the IFs are aligned as best I can make them.
One oddity: the bottom slugs of the T1 and T2 transformers act like they are microphonic, if that makes any sense.  It seems touching them makes odd noises and not like static as a bad connection would. Since this is a 50+ year old radio, I was very gentle and just left them alone at where is looked like a very broad peak. So there is the saga of the IF alignment. Not every mystery was solved. Why did the signal level collapse when connected to the grid of the mixer through a small cap?   Darned if I know.
Tomorrow's adventure is the front end alignment. Should be some fun.      73, Jim
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KD1I
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« Reply #34 on: September 06, 2014, 12:16:44 PM »

Finished at last. My thanks to all who gave me suggestions and encouragement along the rocky path.    Aligning the front end was a piece of cake compared to the 60 KHZ IF.    I never did find out why I could not inject a signal to the grid of V2 but using the grid of V1 worked so I don't question success.  Some of the adjustments were a mile off and others needed just a tweek.  As for dial linearity, I will chalk it up to "that's as good as it gets". After aligning by the book and seeing just how much it ran out across the dial top to bottom, I went back to each band and set it dead on in the middle of where I plan to work.  Plus or minus 100 KHZ and it is only off by very little, a KHZ or so and I am pleasantly surprised. Right now I'm listening to the Ohio State Parks on the Air contest and some DX stations. I am doing an A-B comparison to my FT 2000 and it's not bad.....a rather warm sound. Tuning SSB is touchy and reminds me of receivers I've owned years ago. Now all I need is a matching 60s era transmitter and I'm all set. Well, maybe a reproduction clock.      Many Thanks and 73 to All, Jim     
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AC5UP
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« Reply #35 on: September 06, 2014, 12:34:34 PM »

BTW:  When all else fails there is one quick & dirty method to inject a signal into a mixer or IF that's almost universal...........

On any schematic you'll see the plate connected to the next stage though a condenser or coil. What if someone wrapped a few turns of wire around a tube and fed that from the output of a signal generator? They'd probably couple some RF into the plate as that is the outermost element of most tubes. With the exception of shielded and metal tubes this will work well enough and every once in a while you'll see this suggested in the alignment instructions as 'gimmick' coupling.

The downside is that Q & D coupling can be sensitive to hand or body capacitance as well as any movement of the coil & test lead combo. Might even see a slight change in level as you turn your head to look at the 'scope but if you pay attention you'll figure out what's real and what isn't.

Congrats on getting the radio lined up....!
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W9GB
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« Reply #36 on: September 06, 2014, 12:51:46 PM »

Telechron clock used in HQ170.

As part of Jack Welch's disposal of General Electric's manufacturing operations in 1980s, Telechron was sold to Timex.  Timex eventually closed the original plant in 1992.

IF you have an original Telechron motor -- these can be repaired, often by replacing the rotor.
Telechron Repairs: Hillsboro, Oregon
http://telechronclock.com/page3.html
This clock technician performs repairs and has some NOS parts as well as re-manufactured some key parts.
http://telechronclock.com

Examples of BAD Repairs by inexperienced technicians / consumers
http://telechronclock.com/page12.html
« Last Edit: September 06, 2014, 12:56:27 PM by W9GB » Logged
KD1I
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« Reply #37 on: September 06, 2014, 02:23:16 PM »

Nelson, that idea of the gimic is a good one. I should have thought of that.  In fact, since everything is still open on the bench I'm going to see if it would have worked in this case.....just for future reference.   It's amazing how well these old gals work when they are at last, properly aligned. It really is quite sensitive.
Greg, I don't have a clock to fix. It is the 170 without a clock but it looks so nice otherwise that the blank white place is just begging for a clock. I understand that at one time a replacement reproduction could be had. The mechanism is not the issue because I could purchase a clock at the right size from a hobby and craft store like Hobby Lobby. They have many sizes and shapes of battery powered analog clocks. What I really need is the proper clock face with Hammerlund logo.  So off to the web for a search I go.

Very Best of 73, Jim
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W9GB
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« Reply #38 on: September 06, 2014, 08:19:08 PM »

See if Chuck, K1TLI is still making a reproduction clock.
He was offering that service a few years ago.
http://www.johnsonradioresto.com/Services.html
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