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Accuracy of HRO NPW Dial and Gear Box?




 
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Author Topic: Accuracy of HRO NPW Dial and Gear Box?  (Read 573 times)
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N2CQR
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« on: January 10, 2019, 06:30:24 AM »

I have one of these, and I liked it so much that I build a simple superhet just so that I could put the dial and gearbox to good use.   

But I have a problem with it.  Say I have a very stable signal zero beat at a specific point on the dial.  Say 370 in one of the little windows.   If I then tune around a bit and then go back to 370, my stable signal is no longer at zero beat.  It may be.  But it is often 1-2 kc off.

It seems like the dial/gear box -- is just not that accurate as a freq readout device.

I have gone into the gear box, cleaned it and lubricated it.  And I have tightened the spring.

What do you guys think?  Is this a problem with my particular unit?  Would further adjustment help?   Or is this an inherent problem with a device from 1934? 

Thanks,  73  Bill N2CQR
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MikeKE0ZUinkcmo
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« Reply #1 on: January 10, 2019, 09:54:21 AM »

Have you approached your original frequency coming from both above and below freq?   

If you're using the original cap assembly, have you cleaned all the ground wipers and adjusted the end play in the cap shafts?

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Mike KE0ZU

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Jim, W5JO
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« Reply #2 on: January 10, 2019, 10:33:37 AM »

https://www.prismnet.com/~nielw/PW_NPW_Dial/hro_dial.htm
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Detroit47
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N8QPC on your AM dial


« Reply #3 on: January 10, 2019, 02:46:50 PM »


Do you approach the number turning the dial the same direction every time?  This will insure that the backlash is always taken up the same direction. This is something that is done when running old machinery such as mills and lathes. This always helps with reputability. It is standard practice when running a manual machine.

73 N8QPC
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WBear2GCR
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« Reply #4 on: January 10, 2019, 03:11:10 PM »


Any way to use a freq counter to measure the frequency that the tuning cap controls??
I'd start there if possible... I presume it runs an oscillator?

Lacking that a high accuracy capacitance meter might show if ur at the same spot each time...

                 _-_-
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_-_- bear WB2GCR                   http://www.bearlabs.com
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« Reply #5 on: January 10, 2019, 04:14:29 PM »

Bear:

There is a backlash adjustment for the split-gear in the gear-box. Could be old grease binding things up too.


Dan
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N2CQR
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« Reply #6 on: January 11, 2019, 11:33:38 AM »

Pictures of my project can be found here.  Scroll down for more articles on the HRO-ish receiver: https://soldersmoke.blogspot.com/search?q=HRO+receiver

Thanks for all the info.  I think it is important to remember that there were TWO varieties of HRO gear boxes -- NPW and PW   "Not Parallel With" (the front panel) and Parallel With (the front panel).   I think the NPW was the kind that went into the famed HRO receivers that helped win WWII. 

I am dealing with the NPW variety. Were these gear boxes ever used in National receivers?  Or were they made available just for homebrewers?  If they were in receivers, it would be interesting to see if the calibration accuracy problem was mentioned in the receiver manual.

I have tightened up the mesh on the gears.  It is quite tight. 

I have tried the "approach from the same direction" tuning method.  It does seem to help, but not completely.  And it would in any case be a less than optimal solution for radio amateur.   Do you think that the problem I describe is a function of age and wear?  Or was this the way it was designed? 


73  Bill N2CQR
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WBear2GCR
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« Reply #7 on: January 12, 2019, 10:36:53 AM »

Step one:
attach freq counter to VFO output
Step two:
check frequency while tuning and moving dial
- so, tune to frequency X.xxx, then move the knob gently in the opposite direction.
Does the frequency change immediately, or does the knob move a bit BEFORE the frequency changes?
That's lash somewhere...

Step three:
go to the mechanical side - decouple gear box from VFO capacitor, grab output shaft
with vise grips (probably best to put a metal shaft coupler on output shaft to protect it
and then hold the shaft to prevent from moving, while very very gently turning the front knob - this will
show the total lash.

Actually, I'd try this first with a good size KNOB on the output shaft, and hold it by hand, just to see if you
find lash...

Also, you can run the vise grip clockwise (for example) until it hits something (making contact
with a surface) and then counter-clockwise, noting the lash due to the mass of the vise grip,
and where it ends up on the dial counter each time it goes back and forth.

You might be able to determine IF the gear drive/knob indication is consistent or not.

Also, does the thing end up the same offset, each time you tune from a particular
direction? Or does it vary?

BTW, nice blog! Cheesy
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N2CQR
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« Reply #8 on: January 12, 2019, 04:47:14 PM »

Yea, putting a counter on the oscillator shows the same inconsistency in freq readout that I observe when listening to signals.

Your suggestion about holding the shaft from the gear box to the variable cap was a good one.  I did, and with that shaft completely stationary, I could still turn the main tuning control and could see the gears moving. 

It's not so much 'las as it is "play."

The gears are tight, but I can still move the main tuning knob one or two dial divisions WITHOUT this resulting in movement of the tuning cap.  That's the problem.

Any thoughts? 

Thanks,   73  Bill N2CQR
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N3GTE
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« Reply #9 on: January 12, 2019, 10:44:14 PM »

> Were these gear boxes ever used in National receivers?

Yes both styles were used. The HRO had three shafts, one out the left and right side plus one out of the front for the dial. Both the NC-100 and 200 series used the two shaft model, shaft in the front for the dial and one out of the back. There were a couple of other too the 1-110 and HFS come to mind.

I have a similar issue w/my '36 HRO it seems to have some slop in the gearbox. I'm thinking that it's going to have to come apart and shim the worm gear assembly. I have a spare but I haven't check to see what kind of condition it's in.

GLOM
Terry N3GTE
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WBear2GCR
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« Reply #10 on: January 14, 2019, 09:43:42 PM »

Yeah... I've not had one apart.
There may be a teardown online or on yoohootube?
Seems to me like I have seen that...

The idea of the worm gear needing a shim sounds like it might be something to look at.
Now I'm curious.

Wonder what the backlash adjust that Dan was referring to takes up?

If the worm gear sits one end on a point, one with screw threads, then it can be
adjusted.

Otoh, it may have simply been designed at a time when the tolerances were just not
needed??

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w8khk
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« Reply #11 on: January 14, 2019, 09:58:50 PM »

Yeah... I've not had one apart.
There may be a teardown online or on yoohootube?
Seems to me like I have seen that...

The National dial drives were designed for accurate resetability, and include multiple gears loaded to minimize backlash.  The gear reduction makes it a pleasure to use for receivers and VFOs.

RadioBlvd has detailed information regarding the dial and both gearboxes.  Half way down this page is the data for the HRO style gearbox and the PW dial.  

https://www.radioblvd.com/National%20HRO.htm

Half way down this page is the data for the NC-100 style gearbox, and more data on the dial.

https://www.radioblvd.com/NC100.htm

I do not think there is a link directly to the desired section of the page.   It is a long scroll, but you will find it!

These instructions cover assembly, lubrication, adjustment, etc.  If your drift problem is mechanical, and related to the drive train, then this resource will probably help you resolve it.  GL.
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Rick / W8KHK  ex WB2HKX, WB4GNR
WA4WAX
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« Reply #12 on: January 14, 2019, 10:25:51 PM »

I have a  HRO-50R1.  When received, the gearbox was stiff and troublesome.

I opened the gearbox up, and dug out the bulk of the old congealed grease.  Next, I sprayed the gearbox generously with engine degreased, and set it aside for a couple of days.  The final cleaning was easy.  Next, some PTFE grease from the Tufoil folks.  Lubriplate would also be FB.

I aligned the PW dial zero as per the manual if memory serves.  After 4 or 5 iterations, I got the window zero to coincide with the pointer mark.  The beast is still going strong.
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W7TFO
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« Reply #13 on: Yesterday at 12:13:15 AM »

The anti-backlash feature was mentioned previously, here is a bit of knowledge to flesh the concept out.

It uses a pair of thin gears that look like a single gear.

They are mounted adjacent to each other on the same shaft, with a spring stuck in a small milled recess in both gears.  

As only 1/2 of that gear pair is keyed to the shaft, this puts the two sets of the teeth in a bit of opposition; keeping repeatability high by snugging things up.  

This is not doing the same thing as shimming shafts to force two opposing gears together.

73DG
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Tom WA3KLR
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« Reply #14 on: Yesterday at 08:01:56 AM »

What is frequency range of the receiver from 000 to 500?  (I don't think you stated.)
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
WBear2GCR
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« Reply #15 on: Yesterday at 09:12:15 AM »

For reference the image is below.

The split gears (spring loaded) will always have zero lash, within the force range where the
force does not exceed the spring pressure.

The worm gear, as shown, uses a spring to provide the "zero lash" situation.
I'd look closely at that arrangement.
IF the spring/bearning/shaft arrangement is not friction free, one might get some unwanted
variation in the worm gear position - or if the spring is shot or broken, same thing.

I'd have a good look at it, and clear it out and use synthetic lube going forward.

(someone suggested Lubriplate? I'd advise against ever using it, as it has a usable life of
only 5-10 years in many cases, thereafter it hardens. Today we have synthetic lubes that
never gum or harden)


* HRO GEARBOX.jpg (115.28 KB, 640x447 - viewed 14 times.)
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WA4WAX
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« Reply #16 on: Yesterday at 11:58:16 AM »

I stand corrected on Lubriplate.  Thanks!
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N2CQR
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« Reply #17 on: Yesterday at 04:55:18 PM »

Thanks again to all who offered advice and assistance.  With help from you guys -- and from Pete Juliano N6QW, I think I have this fixed. 

The problem was really with the variable capacitor.  The one I was using was kind of stiff and irregular in its motion.  I found another one in the junk box that was easier to turn (it has one set of ball bearings).  This fixed most of the problem.

I also spent more time making sure the shaft of the cap lined up perfectly with the shaft of the gear box.  This also helped a lot.

I realize now that some of the "stickiness" that I occasionally feel while tuning may be coming from the dial -- not from the gear box.  It looks like my dial took a hit that slightly bent one portion of it.  It seems that the numbers have a bit of trouble clicking over on that portion of the dial. Some lubricant may help there.  But I can live with it.

The receiver now tunes very smoothly and I can go right back to a frequency and find the signal exactly where I left it.  There does seem to be a very slight difference depending on whether I "approach from above" or "approach from below" -- but this is not a big deal.

James Millen knew what he was doing. 

73  and thanks   
Bill N2CQR
http://soldersmoke.blogspot.com
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