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Author Topic: Heathkit SA2060 Tuner Inductor Coupling Slippage  (Read 2930 times)
KA4KOE
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« on: June 14, 2011, 09:39:24 AM »

I have an SA-2060 and its attendant issues with inductor shaft coupling slippage.

I have tightened the hex screws to the point where the wrench strips the screws, and still the shaft loosens up after a short amount of use. I have attempted to make sure the shafts line up to avoid any flexure.

Thoughts:

1. Why not replace the 6/32 hex screws with standard machine screws of the same thread, either flat or Philips head?

2. Has anyone tried drilling a small, shallow hole in the inductor shaft, large enough in diameter such that the set screw will have something to bite on, and prevent slippage?

3. I am aware of the couplings that have two hex screws per side that effectively double the gripping area, but don't know where to find them.

4. Is there a tension adjustment on the inductor that will loosen up the force necessary to rotate it?

Thanks

Philip
KA4KOE
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KI4VEO
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« Reply #1 on: June 14, 2011, 06:11:57 PM »

I own a 2060A but I think the L1 rotary inductors are similar in construction.  The inductor friction level is controlled by a screw threaded into the REAR shaft.  There is a bushing on the inner side of the plexiglass panel that the inductor shaft passes thru.  The outside of the bushing is threaded and a nut threads over the outside of the bushing on the outside of the plexiglass plate.  The level of friction is adjusted with a screw which threads INTO the rear shaft and squeezes down on the outside of the end of the bushing.

Remove the set screws and get a small tube of Locktite blue (low pressure thread lock breakaway - the Locktite red requires a big wrench to break it free).  Auto Zone and other auto parts stores carry it.  The Locktite blue will prevent the set screws from loosening under normal use.  Just a single drop on each setscrew threading will do the trick.  Carefully thread the setscrews back in place.  If in doubt, once the setscrews are partially installed, apply another single drop to the top edge of each and finishing tightening.  The Locktite will wick down the threads and set up in a short time.  Normal vibration will not cause them to work free.

You may also wish to use some silicone spray on the front and rear shaft bushings and the roller pick-up wheel.  I would not recommend WD40 or any other type of oil.  They have electrical insulating qualities - the silicone spray does not.  I purchased a 7 oz.can of CRC with an extension spray tube (helps to get into tight spots) @ Home Depot for around $4.  Works well on roll-up garage door wheels, too.  Doesn't attract dirt and lubricates nicely.

SmallParts and McMaster Carr carry the "two hex screws per side" style couplings you refer to in your posting.  They are available in plastic and stainless, slotted and non-slotted, and aren't cheap.

Out of despiration I made one (not for my 2060A but for another tuner - a Nye Viking MB-IIA).  A piece of appropriately sized steel tubing, drilled at the correct locations, and a metric tap to cut the threads for the set screws.  Necessity is the Mother of Invention.

Hope this helps.

Howard Walker
KI4VEO
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K8AXW
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« Reply #2 on: June 17, 2011, 10:02:56 AM »

You coupling slippage is a common problem with high load components.  The fix, after insuring the shafts line up is to either replace the existing single set screw coupling with a dual set screw coupling or modify the existing coupling.

Personally, I prefer to simply remove the existing coupling and drill and tap the coupling for the second set screw.  I put the second hole approximately 45 degrees from the first.

After that, I paint the knob shaft with a felt tip pen, let it dry, insert it and rotate it to the proper position and then run the two set screws in against the knob shaft.  Back off the set screws and remove the knob shaft.

I then drill an indentation into the knob shaft where the set screws have marked it.  The indentation is made by a drill bit a little larger than the set screw and as deep as the angle on the drill bit tip.  In other words, it isn't necessary to drill a 'hole.'

I've never had a shaft slip after this modification.

Plan B would simply be to either obtain or have made a new shaft coupling (I've had them made too!) with two set screws.

Adjusting the friction contacts on a roller inductor is touchy and should be avoided unless you know that someone has messed with it or the inductor shows to be intermittent using am analog meter.  Lubrication is definitely a good thing to do but be sure the lubricant doesn't get on the slip ring contacts or roller/roller shaft.  They both should be cleaned with a nonresidual cleaner.
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W8JX
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« Reply #3 on: June 17, 2011, 05:51:50 PM »

Simply use a file to cut a small flat spot/bevel where screw tightens into.  Quick and easy to do and no need to drill anything.
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KB2CPW
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« Reply #4 on: June 21, 2011, 11:31:32 PM »

Simply use a file to cut a small flat spot/bevel where screw tightens into.  Quick and easy to do and no need to drill anything.

  Bingo.. And a light silicone spray all of the rotating components since they do tend to get tight. Works for me. Richy
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KM3F
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« Reply #5 on: July 01, 2011, 01:40:07 PM »

I have been all through the little things with this tuner as well.
For the shaft coupling on the roller inductor, I finally machined a new longer steel coupler with double set screws in 6-32 size both ends.
That fixed it for good.
Had to adjust the drag in the tuning caps for being to loose.
The sliding roller connection and tension had to be addressed.
I ordered an external roller fast use crank from Ameritron and glued an  GM auto master cylinder cap machined in the center to accept the crank to it for a nice look and faster roller operation.
Looks like factory.
Been a very good tuner all the way up to 6m on a 75m dipole and anything in between.
The power meter and swr function is quite good as well.
Put LED lights on the tops of the meters inside for low light use, powered by an adjustable DC regulator circuit wired on a single terminal strip.
May some time add a peak reading power board.
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K9YLI
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Posts: 850




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« Reply #6 on: July 17, 2011, 08:14:50 AM »

 true of any  set screw  coupler,,   

if the  coupler is  thick enough,,     use  two set screws , one o top of the other.. use a very  short one for the inner one,, adjust the shaft and thighten,, then  put in second screw, it can be as long as you like and still clear surronding   stuff..

same as putting a double nut on a bolt and tightening them aganst each other.


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