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Collins KWS-1 Plate & Ant Tuning Controls REPAIR - PRELIMINARY




 
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Author Topic: Collins KWS-1 Plate & Ant Tuning Controls REPAIR - PRELIMINARY  (Read 776 times)
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WBear2GCR
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« on: April 08, 2018, 07:32:20 PM »

Having just acquired a KWS-1 of early manufacture, I found the Plate and Ant tuning
controls to seize or be rather un-smooth. Apparently this is a common problem.

So, after checking online and finding not much good information on a repair, I investigated myself.

After determining what the problem is, I came up with a few methods to effect high quality repairs.
It's PRELIMINARY because I just wrote this up, and have yet to implement the repairs, and take pics.
I'm confident of good results using these methods.

I wrote them up, and they're in the attached pdf. (A high res version is available on request)

Comments, reactions, feedback and suggestions appreciated!

Feel free to share or put this pdf online, with attribution, please!

Repairing these knobs properly is essential to keeping these rigs on-the-air.


* KWS-1 BEAR.JPG (609.03 KB, 1480x1973 - viewed 74 times.)
* Repairing the KWS KNOB - small.pdf (381.22 KB - downloaded 82 times.)
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« Reply #1 on: April 10, 2018, 04:07:54 AM »

years ago I bought a KWS1 that had worn out plate/load verniers .... It had pot multiturn counter knobs as replacement ....worked fine and looked good .... your work is better by far but this is a possibility for repair
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WBear2GCR
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« Reply #2 on: April 10, 2018, 12:44:21 PM »


Yep, I've looked at that, but the issue there is that the knobs on the typical multi-turn pot counter dial
are much smaller diameter. Also, I'm not certain but I think these resolve to 100 places vs 10 turns...
but that might be only because it's a continuously reading dial, might work out the same, other than knob
size.

Purists want the original look, of course.

Hopefully before too long I'll have pix up of the actual repair work incorporated into the pdf.

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« Reply #3 on: April 11, 2018, 08:45:28 AM »

Very nice explanation. On my first real job I had an old German boss who was a mechanical wiz. I learned so much from him. Your explanation and the possible solutions reminded me so much of him!
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« Reply #4 on: April 11, 2018, 09:49:58 AM »

Back when I had a KWS-1, this was the most frustrating part of owning the d*** thing.  I ended up borrowing the two reduction knobs from a 180S-1 I had purchased several years before for almost nothing.  Those were in good shape.

Also, several (15?) years ago, a CCA member was selling the reduction assemblies from the PRC-47 as a solution to the KWS-1 issues.  They had the small knob, and a slightly different scale, but otherwise would work.  I bought a couple of them, but never used them .. not sure what happened to them.  In any case, my understanding at the time was that the KWS-1 assemblies had a "small" knob, too, and the large one you see is actually some kind of cap over the small knob and could be removed and shifted to cap the PRC-47 assembly.  At this point, since the older I get the less I remember, I can't say for sure that that is the case or would actually work.

It's too bad there isn't a way to install a couple of quality 6:1 verniers behind the panel with an original appearing knob.  It would make it a whole lot smoother to change bands .. without having to consult a chart first, and then cause wrist damage cranking those old verniers to the new spot.  Rapid band change was definitely not a design criteria for this transmitter :-)

Hope you can find a good solution to rehabbing those things
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WBear2GCR
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« Reply #5 on: April 11, 2018, 09:44:54 PM »

<snip>

It's too bad there isn't a way to install a couple of quality 6:1 verniers behind the panel with an original appearing knob.  It would make it a whole lot smoother to change bands .. without having to consult a chart first, and then cause wrist damage cranking those old verniers to the new spot.  Rapid band change was definitely not a design criteria for this transmitter :-)

Hope you can find a good solution to rehabbing those things

There's no need for a vernier behind the panel!
As far as I can see the panel thing is a counter ONLY.
The gear reduction takes place back in the PA sub-chassis, there are gears in there.

I'll look into the PRC... yes the knob does get screwed on with a center set-screw right over a smaller
"knob" thingie.
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« Reply #6 on: April 12, 2018, 04:01:15 PM »


UPDATE #1

(will be incorporated into the final pdf...)

Pictures to follow too.
Bored the shaft hole in the knob today.
Made a holder for the lower half of the knob first.

Guess what?
Turns out the bottom half is NOT pot metal!

Or in the words of Private Gomer Pyle "su-prize su-prize, su-prize"!!

Turns out that it is actually cast brass!
The pot metal look comes from what was likely at one time a bright zinc plating
on it. That was probably to give the outer skirt's numbers and graticule lines a silver look.
Since that time, it's dulled considerably. Thus the look and feel of genuine pot metal.

Well, next to see if I can make an insert or not. Cheesy

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« Reply #7 on: April 15, 2018, 09:14:06 AM »

Many years back I obtained a KWS-1 and of course the knobs were messed up. I have been a toolmaker for a hundred years, so it was a good challenge. I made a solid aluminum fixture that the knobs would sit in securely and the center located very accurately, and located radially by using the set screw hole so I could red-rill it later.. I had some end mill cutters ground to a few sizes that I thought would work to re-size the hole and repair the out of round. Then, on a Bridgeport vertical milling machine, I bored the hole out as far as I thought was safe. I then filled the back of the knob and hole with aluminum base JB Weld, avoiding the area where the gear is. By filling the void around the repair, it added some support to the wall of the hole. After letting this cure a couple of days, I re-bored the hole to the proper size, plus a thousandth or two. My fixture was made so I could also use it to re-drill the set screw. Success. I re-installed the knobs and they worked great. I still avoided over torquing them on installation tho'. Since the knobs are pretty much scrap and useless until repaired, I thought to offer my service and repair to others. Now understand, I offered this for free since I already had the tooling made up and the repair was simple. Just send me a buck or two for postage. I explained the repair that I did. I repaired a few for guys, warned them of over torquing the set screw, and they were happy to get otherwise useless parts repaired. Then....it started. I received some nasty e-mails from Collins Collector "experts" accusing me of trying to make money off of the repairs and also destroying or damaging valuable Collins parts, by rendering them "non-original". That was it. Screw it. I withdrew my offer to fix anymore at any price, and even tho' I still have the tooling somewhere I think, I stand by that decision. The repair must have worked, as I never heard of any  failures to repaired parts.  I am posting this so someone who has the skill can re-duplicate or improve what I found to be a solution and repair some otherwise useless parts to a pretty cool old transmitter.
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« Reply #8 on: April 16, 2018, 12:18:57 PM »

Heh... I suspect that many of those "purists" are now SK anyhow?

But, yeah, after more thought, It was also my idea to 'backfill' the open voids behind/around
the bore for the shaft. Yet to do that though.

I too made up a holder for the knob. I used 1.250" aluminum bar stock, and drilled, then bored
it on my lathe. I've bored the hole in the lathe after that. Seems to have come out very nicely.
I'm holding the knob in place with the set screw hole in the top that connects the knurled part to
the lower skirted dial part.

I'll have pix of the whole deal once I finish the "insert" and put it in place, and it works properly.

As far as "making a profit" off repairs? WTF does Howard Mills do??
Hard to understand what they were complaining about. I'd not have bowed out quite
so quickly on that. In fact, had I known that you had done this more or less before I came to it,
I'd have sent mine to you!! :p

But I'd have missed all the fun then! Cheesy

                                     
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WBear2GCR
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« Reply #9 on: April 18, 2018, 03:05:18 PM »

Lathe fixture for holding KWS inner knob for boring.


* KNOB LATHE FIXTURE.JPG (409.87 KB, 1480x1110 - viewed 26 times.)

* KNOB LATHE BORING HOLE.JPG (404.69 KB, 1480x1110 - viewed 33 times.)
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WBear2GCR
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« Reply #10 on: April 18, 2018, 08:25:50 PM »

Virtually unobtainium:



* HELIPOT R-10 PARTS.JPG (310.13 KB, 1480x1110 - viewed 40 times.)
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WBear2GCR
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« Reply #11 on: April 19, 2018, 07:59:13 PM »

Updated version. V 1.2 contains more information.

The actual insert has not yet been added to the documentation.
Soon.

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* Repairing the KWS KNOB v1.2 .pdf (349.25 KB - downloaded 10 times.)
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« Reply #12 on: April 19, 2018, 11:21:54 PM »

I read your entire file.  Looks like a lot of work to fix the knob.  Your probably right about the shafts being a little short causing the failure in the first place.

I would bore the knob like you described.  Then make a new shaft that is oversize out of brass.  If the shaft has to be .250" passing through the rest of the knob assembly and panel, then turn the oversize shaft down to .250" on the part that exits the knob.  The new shaft can be short, just enough to get into the chassis area.  Use another piece of shaft material to reach the coupler.  

The new brass shaft can be soldered to the brass knob.  Or, you could carefully locate the spot where the set screw hits the shaft.  Then drill and tap the new brass shaft the same size as the set screw.  This will remove the pressure on the side walls of the bored out knob.

You can use another 1/4" union to connect together the two new pieces of shaft material.

Don't overlook using the shafts from old controls.  The pots have collars that can be pinned to the shaft.  Once pinned, turn the collar down to the size of the bored out knob hole.
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WBear2GCR
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« Reply #13 on: April 20, 2018, 01:36:43 PM »

Thanks.

Your scenario was considered, and is mentioned in the pdf. Cheesy (V1.2)

There is a problem with merely boring and making the shaft end larger, and that is that the knob's bore is now
weaker than before.

One could pin a collar, but that's far more effort than needed. It's way easier to start with a larger diameter length of
stock, and turn the shaft down the 0.250" except for the part that goes into the knob. Or bore a short section of that same
bar stock to fit over the end of the 1/4" shaft. I'd turn the shaft down at the end, maybe to 0.200" then put a hole in some
stock, reamed just at an interference fit and then heat the short section, freeze the shaft, and <WACK> or press
fit them together. Then turn down that assembled piece. This way there is no slop and there is meat to take
down to fit in the widened bore (typically ends up 0.265" +/- depending on the knob).

I would not rely upon the setscrew without an insert that strengthens the brass bore. Which is why I'm not
going for this method.

At present I am doing the first insert using brass, but the next will be either steel or stainless - for strength.

Also, I have another method to add strength. That will have to wait until after I do it before it is presented.

Soldering to the knob risks overheating the knob and destroying the paint, or if it gets hot enough the zinc
plating. Also solder, at least electrical solder is prone to stress crack, so is not a great choice in that regard,
plus it is a soft metal. So, I discounted that method.

Yes, it is a fair amount of work. Most of it has been in the research, figuring out the method, and then writing it
down. Anyone with a lathe and some machining experience can knock this out in fairly short order.

The problem is that an owner of the KWS-1 with ANT and PLATE knobs that are not working well has no choice
but to repair or replace them.

In the pdf (v1.2) I've figured out and shown what the mechanism is from the OEM, an astute observer no doubt
can determine where and how to locate used, low hours examples of them. Cheesy
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WBear2GCR
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« Reply #14 on: Today at 12:53:07 PM »

Uh-oh.

Something very strange.

Was cutting a properly sized diameter for a brass insert, the first one I had made too small a diameter.
Tried it on the knob - very tight fit, which is good. Pushed and turned it to slide it on. Pulled it off.

Look at what I found!!

Yep, that's an insert made of plated brass!!
Not only that it has a hole for the setscrew and it's got markings on the surface too!
It pulled out of the knob and stuck to the piece I was machining!

So, my finding that the knob is zinc plated brass is wrong.
Yikes!

Now, it looks like the knob is cast Aluminum. Which changes everything.

More than one knob seems to evidence the brass insert showing color. Others upon close
inspection with a 10x eyeloupe do NOT. No idea what the deal is with that.

I have about 6 knobs total, most are not in good shape, fyi.

Also, with the 10x eyeloupe on more than one knob there appears to be a small stress crack on the shaft hole side next to
the gear. The crack does not appear to have migrated deeper into the shaft hole though.

So, change of plan. Looks like I'm going to go with a stainless steel insert rather than brass or steel.

Well, who knew?

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* INSERT FOUND.JPG (248.29 KB, 1480x1121 - viewed 13 times.)
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