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 Post subject: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Tue 11, 2019 12:24 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
I've dscovered a problem with the vernier tuning shaft. Referring to the photo, the silver end of the shaft is some sort of reduction drive compared to the brass colored inner part of the shaft. But the outer silver end just turns and turns and does nothing. What could be wrong? I don't know how if the assembly can be taken apart for investigation, but right now of course, the vernier function is worthless. Any ideas? Thank you.


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Tue 11, 2019 12:59 am 
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Small ball reduction drives like this have very little torque transfer capability so make sure that the capacitor it is trying to turn isn't stiff/stuck.

I have cleaned and greased several different varieties of reduction drives but I haven't been inside that particular Hammarlund part. With time, the old lubricant dries and picks up grit so you have to clean and replace with new grease.

Rodger WQ9E


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Tue 11, 2019 4:46 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
Thanks. That did it. I didn't consider the variable cap to be particularly stiff, but apparently it was. Now working perfectly. My big regret about this particular restoration was that my buddy slathered navy jelly on the chassis and let it dry 3 months before turning it over to me. Terribly stained. Now I got the chassis clean as a whistle but not a square inch of cadmium plating on it.


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 2:09 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
Being so close to buttoning up this project, upon "final checkout" I have discovered a problem. The 21MC 15 meter band is dead as a doornail. Nothing. Will not pick up even the faintest peep from my signal generator. This is a very complicated radio when faced with a problem like this. Rather than throw my hands up completely intimidated, I endeavoring to think it through. The reason I'm posting is to see if others might poke holes in my reasoning.
If the other bands work, and this is a triple conversion radio on the higher bands, then logically the best place to look for this problem would be in the coils and their capacitors relating only to this band, which logically would narrow down the places to look to just a few places in this huge complicated schematic.
If anybody has some input, I'm all ears. Thank you.
https://www.qsl.net/kb7rgg/radio/schematics/hq170a.pdf


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 2:40 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3680
Location: Monterey California USA
Sounds like the oscillator is not starting on that band. Now the effort can be directed to why...

Not like you will be working anyone on 15 meters in the near future anyway the way the band is.

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Bell System Mobile Telephone History
http://www.wb6nvh.com


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 2:57 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
That was an answer I hadn't thought of and probably wouldn't have. But knowing the reputation the 6C4 tube has in these hammarlund, I plucked out the tube and put in a new one, hoping for simple dumb luck. No such luck though.nothing changed. Just static. My signal generator doesn't even cause a blip on the carrier meter. Stone deaf.


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 3:22 am 
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Couple your signal generator through a capacitor (to block DC) to pin 7 of mixer tube V2, this bypasses the RF tuning components and if you don't hear the signal with that coupling then you can be pretty sure the oscillator is at fault. Just leave the receiver tuned somewhere in the 15 meter band and slowly sweep your signal generator well above and below the selected HQ-170 dial frequency in case the calibration is well off on this range.

If you have a tube socket test adapter then you can do this from the chassis top.

Rodger WQ9E


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 3:56 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
I'll try that. When I got rid of a lot of electronic gear a couple years ago, my extender sockets went too. So now, in a pinch I just get a short lenght of that single stand wire used in wiring telephone jacks in houses. I strip back a little and coil a couple coils around the tube pin and put the tube back in and hook my alligator clip to the pigtail. Works pretty well most of the time


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 4:40 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
A very interesting turn of events, thanks to you guys. This radio belongs to a buddy. He handed it to me to fix along with a tupperware tub of tubes and a tag marked 170 inside, as well a 2 or 3 others I recognized as belonging in a Hammarlund. In that tub were three 6C4 tubes. One was apparently NOS still in the box. Trying each, not only did I have no 15 meter band, but I had lost all the other bands too. Only with the tube that was in the radio did 160, 80, 40, 20, and 10 work PERFECTLY, but no 15. So I think the oscillator theory above was proven. But obviously there's an underlying cap or resistor out-of-tolerance problem, that makes the circuit so picky as to the perfect tube. BTW, I'm fairly new in my club W4BFB, which has 150 members, a lot of them Extra. But so far I haven't met one who knows his hind end from a hole in the ground about tube gear. I guess I must be the resident boat anchor man. That's pretty sad. Look at all the ignorant questions I ask on here. Thanks, men. KN4SMF


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 6:57 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3680
Location: Monterey California USA
Time for an orderly approach to troubleshooting. First, verify if the oscillator is working, one way or another. Either with test equipment or another receiver that can hear it. If it is running, then you can consider something amiss in the front end section. Such as a burned out antenna transformer primary, caused by lightning or a goofed up T-R switch wiring job. I don't know what signal generator you are using and how many microvolts you were putting in to test it. Enough signal will make it past the antenna transformer, even if defective. Hopefully this isn't a case of someone messing up the alignment.

I assume we can eliminate the bandswitch from the issue as you have cleaned its contacts thoroughly and worked it back and forth a sufficient number of times?

I suspect that if the 6C4 you have works on all the other bands, it should work on 15 Meters too. Oscillator issues can be some of the most vexing. I have a bizarre oscillator issue in an RMCA AR-8506 Liberty ship receiver that I had to just set aside for an indefinite time before I wound up in a rubber room.

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Bell System Mobile Telephone History
http://www.wb6nvh.com


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 3:04 pm 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
Found my problem! Sure enough it was the 6C4 tube. Took the one out of my own 170 and it worked like a charm. I believe that keeping 2 tubes lit in the A series is a big mistake. Now I need to figure out how to wire this radio for all tubes to be dead till the radio is turned on


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 3:30 pm 
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Sounds like it was a weak 6C4 tube where the oscillator wouldn't quite take off on 15 meters.

It is easy to change the 170A auxiliary filament transformer wiring, you want it where its primary is in parallel with the main transformer primary and this only requires moving one primary lead for the auxiliary transformer from its current position so that it is on the switched side of power switch.

Rodger WQ9E


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 5:14 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3680
Location: Monterey California USA
Weird cause but at least you found it.

I had to rewire my Hallicrafters SX-101 Mk III for a similar reason because otherwise the always-lit 12BY7 after 6-8 months of non-use would have a short every time I went to use the radio and I got tired of spending money on tubes.

_________________
WB6NVH
California Highway Patrol Radio
Bell System Mobile Telephone History
http://www.wb6nvh.com


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Mon 24, 2019 6:23 pm 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
I ordered 3 6C4 tubes tested good from a guy in Massachusetts. Hopefully 1 will work. But anyway on my question regarding wiring the heater transformer for V2 & V12 to be turned off with the rest of the radio, I've photoshopped an excerpt from the schematic to kindly ask for double-checking my thinking. If I didn't have sites like this to ask simpleton questions of, I'd probably just get out my voltmeter and take my best shop. But since you guys are here... I'm thinking disconnect at the red arrow and moving that transformer connection to the bottom contact in the red circle.
I know I've hammered the forum about this radio. But you should have seen what a mess it was when I first got my hands on it. Much of it I figured out without asking questions. Now this radio is looking really good. I'm only sorry I don't have a signal generator that will do 60kc's. But I do have to say that it does seem pretty accurate on the dials. Maybe I'll do an RF and antenna coil tweeking with my generator though.


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Tue 25, 2019 3:01 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
Discovered I didn't post my drawing with the above question.


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Tue 25, 2019 3:05 am 
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That is the correct point Henry.

Rodger WQ9E


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Sat 29, 2019 1:26 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
Well the used tested good 6c4 tubes I ordered off eBay came today and the first one out of the box restored all my bands to working. I guess it goes to cement the idea that engineering the radio for 2 tubes to stay lit wasn't a very good idea. 1 tube in the radio and 3 spares that came with it, and none of them worked tells the story loud and clear.


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Sun 30, 2019 1:34 pm 
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Joined: Feb Mon 04, 2008 3:20 am
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Location: Coopersville, MI 49404-9643
Just a note here, that comes from Hammarlund. The tubes filaments were left on for two reasons. First, to deal with start up drift. Second, it keeps all the IF, OSC and RF transformers dried out. HUH?? you say. YUP, the coils WILL absorb moisture and the radio goes out of alignment. Let one of these things set around for 6 months in a humid environment, and you will wait another 6 months to get it dried out so it works again. OR you can have the joy of re-aligning the receiver every two weeks for the next 6 months.. Your choice. Personally, I'd leave the RF and 1st mixer tube running, and drop the 6C4 oscillator off that bypass heater string. You'll put up with some drift, but you WON'T be chasing your tail forever on realignment. Hammarlund went to that scheme to stop the drift complaints and it also stops the realignment grief. BTW, I had the fun of trying to fix a 180A that some genius used Naval Jelly on as well. I SCRAPPED it. The Naval Jelly ate the bottoms out of a bunch of the IF cans. The customer got a new radio that I found.

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W8ZV
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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Sun 30, 2019 1:49 pm 
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Naval jelly is far "hungrier" than a lot of people realize, think of it by its real descriptor "phosphoric acid" and treat it with respect. I have also seen the damage this can do which will be worse than the rust if used carelessly. Also be very careful with cadmium plated chassis when cleaning them because grinding or sanding will expose you to this toxic heavy metal. I remember early on in my involvement with vintage gear restoration there was a member on the original boatanchors email list who was undergoing treatment because of his exposure to cadmium; he had done a lot of Hallicrafters repairs and prided himself on making the chassis very shiny.

Another option to keep some heat where you want it is to use a "damp chaser" type resistor. Halli used this along with constant on filaments for some tubes in a few of their SSB oriented receivers. One of the resistors designed to heat sink to the chassis would work very well for this, aim for 5 to 7 watts of dissipation when fed by the 120 VAC line and do NOT forget to fuse it just in case.

Rodger WQ9E


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 Post subject: Re: Hammarlund HD 170A Vernier Tuning Knob Problem
PostPosted: Jun Sun 30, 2019 2:39 pm 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 249
1) in 1964 or so when the radio was made, tubes were in infinite supply. Now they are not. 2) in 1964, most people did not even have window unit air conditioning. Now central HVAC is the norm. 3) ham radio is a hobby. Hobbyists are notorious for losing interest, maybe for years, and there was this radio, sitting there burning tubes the whole time. 4) this radio came to me with it's history in a Tupperware tub. Testimony that it indeed a tube eater by design. 5) I could go on...


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