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Author Topic: Dentron GLT-2000C: Vernier tuning dials not turning Air Caps  (Read 1847 times)
N2EYE
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Posts: 85




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« on: June 20, 2013, 05:07:25 PM »

Hello,
   I recently bought an otherwise   mint condition ATU by Dentron.  Looks like it was  never  used,came w/ original papers  and it worked great.  After 2-3 months of light use,  the C-In and C-Out dial-reduction controls fail to move the  variable air Caps inside.  They get increasingly stuck.

I remove the plastic  knob   and turn theoutside collar by hand to get it moving again.  So far tried a few drops of motor oil.

I am reluctant to try and fix this.  If I cannot turn the Caps inside it is useless  so I guess it's time to open the toolbox.

I  have a  GLT-1000  parts unit that seems to usethe same controls.   My hands are weak  and very shaky.  I dread the prospect of somehow  making it worse.  Never had this problem with my prior Dentron (parts unit).

Any suggestions??  neil, n2eye
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K8AXW
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« Reply #1 on: June 20, 2013, 07:19:47 PM »

Neil, Clint Eastwood, aka, Dirty Harry Callihan said, "A man's got to know his limitations!"  That's good advice.

It seems to me from your description that something is slipping.  It should be somewhat obvious what that "something" is because this drive is rather simple.

I would suggest that you really give the old eyes another look at what is wrong.....what is slipping and then see if you can find a set screw to tighten.

Plan B would be to get a local ham to have a look at it for you.  There's no shame in that.   Wink
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KA4POL
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Posts: 1978




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« Reply #2 on: June 20, 2013, 09:50:43 PM »

There also could be a stuck bearing against which the best tightened set screw will lose. I've had success in similar cases using WD40.
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KE3WD
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Posts: 5689




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« Reply #3 on: June 21, 2013, 05:54:33 AM »

Mechanical verniers often depend upon the proper type of lubrication and if that lube dries out, they won't work right. 

Sometimes a bit of oil added can loosen up certain old and dried out lubrication greases, other times the vernier needs to be cleaned out thoroughly with a solvent and a reapplication of the proper type of manufactiurer/designer recommended grease applied. 


73
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N2EYE
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« Reply #4 on: June 21, 2013, 08:14:21 AM »

Thanks Allforthe Replies,
Guess I got what I paid for:  "A like new" 35 year old ATU.  Seems the ball bearings in the Var Air Caps gunked up overthosenearly 4 decades it sat in someone's  closet. 

 I used a few drops of alcohol to clean and re-oil  ball bearings.   I used a small electric drill to turn the cap over until the gunk worked its' way out  of the bearings.

The problem was/is not yet over  as the stiff Caps  weaked the drive reduction units. 
BTW:  This  model  is a GLT-1000C...The watt meter goes   to 2KW on the newer, C-model (ratings too?).  I had a GLT-1000 that I used until it fell apart but fortunately kept it for parts).

As this morning, I swapped one  older GLT-1000 drive unit to the new GLT-1000C  ATU   with re-lubed variable air cap.   

So far,  I only finished 1 Cap.   1 more to go and then (hopefully) happy swr's all around.

neil 
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AD6KA
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Posts: 2237




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« Reply #5 on: June 21, 2013, 09:24:06 AM »

I'm so glad you figured out how to get the Cap drives unstuck.

I LOVE Dentron tuners. They a very high quality build.
I have the Dentron MT-3000A, and I will never sell it,
at any price. They just don't build them like that anymore.
If you ever get a chance to buy a Dentron that fits your needs,
just do it!

73, Ken  AD6KA

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N2EYE
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« Reply #6 on: June 21, 2013, 12:15:11 PM »

Addendum: I finished second Var Air Cap re-lube and   swapped-in another   vernier reduction unit from my Denton parts/older model GLT-1000.

C-Out works great like 100%.   C-In needs a nudge of the dial indicator to keep the Air Cap moving when turning the  vernier reduction  control knob.  Apparently the overly stiff Var Air Caps damaged both  vernier reduction units on my new ATU.   

Dentron’s reduction units are apparently work by friction and is not gear driven.   The Units were sealed by folding tabs of metal I did not want to bend out for fear of them breaking off.   So the notion that “something must be slipping”  is true but with Dentron’s first GLT-1000 ATU through to the GLT-1000C models the slipping is un-fixable without a new unit   to install.
Neil
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AD6KA
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Posts: 2237




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« Reply #7 on: June 21, 2013, 06:40:27 PM »

Quote
So the notion that “something must be slipping”  is true but with Dentron’s first GLT-1000 ATU through to the GLT-1000C models the slipping is un-fixable without a new unit   to install.


Could you substitute a planetary reduction drive like
these, or similar to these 8:1 units? You've have to
double check the ID's of the reduction drive's coupling
side to the OD's of the variable cap OD shafts.
http://www.orenelliottproducts.com/planetar.htm
Ken, AD6KA
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KE3WD
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Posts: 5689




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« Reply #8 on: June 21, 2013, 07:25:34 PM »


C-Out works great like 100%.   C-In needs a nudge of the dial indicator to keep the Air Cap moving when turning the  vernier reduction  control knob.  Apparently the overly stiff Var Air Caps damaged both  vernier reduction units on my new ATU.   


It is more likely that the lubricant you used is not heavyweight enough.  A lot of those type of vernier drives depend upon GREASE to work.  With oils, they will slip.


73
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