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Author Topic: Help with straight key adjustments and contacts  (Read 2517 times)
W9KDX
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Posts: 770




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« on: February 09, 2013, 05:41:18 AM »

I have a new, for me, Vibroplex straight key.  When adjusting the tension on the trunion screws, is there a general rule as to how tight they should be?

Also, what general rules are there for what the contacts should look like?  Mine are slightly rounded and I am used to seeing flat but these work just fine so I don't want to mess up anything.

Thanks
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Sam
W9KDX
K8AXW
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Posts: 3722




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« Reply #1 on: February 09, 2013, 08:22:39 AM »

Sam:  We were taught in the service to adjust the trunnion screws to eliminate any lateral movement while at the same time allowing free vertical movement.

The contacts were adjusted down to the thickness of a postcard.  (QSL card is fine)

The spring tension was adjusted to personal preference for quick lever return but not so tight that it creates fatigue quickly.

These adjustments are a matter of personal preference for the most part as you will find out from answers you will get here.  I've seen keys adjusted with gaps open far enough to crack nuts!  It's whatever you get used to.

I might add that the military way was designed to train many men in a hurry and to set up key adjustments that enabled operator changes with minimal hassle.

Al - K8AXW
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K9AIM
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Posts: 989




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« Reply #2 on: February 09, 2013, 04:43:39 PM »

Here too is a link that I bookmarked long ago that may prove helpful:
http://www.mtechnologies.com/misc/keyadj.htm
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KD8OW
Member

Posts: 4




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« Reply #3 on: February 11, 2013, 04:46:45 AM »

On our ship the trunnions were adjusted just tight enough to remove lateral motion, the contact gap was 4 sheets of paper and the return spring pressure was personal preference. What seemed like excessive contact gap was there to prevent accidental contact closure.

Bill
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W9KDX
Member

Posts: 770




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« Reply #4 on: February 11, 2013, 04:57:23 PM »

Thanks guys, common sense told me that no more than finger tight was the logical degree for the trunnions.  The Vibroplex has slots for a screw driver which made me wonder.

As to the contacts, thanks for the guidelines.  My main question had to do with the shape of the "flat" surface.  Mine are slightly rounded and I was wondering if they should be dressed.

Thanks
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Sam
W9KDX
VA7CPC
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Posts: 2371




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« Reply #5 on: February 12, 2013, 12:46:47 PM »

You _want_ them to be slightly rounded!

The logic:

. . . It takes a certain minimum pressure (pounds _per square inch) to get reliable, low-resistance
. . . connection between the contacts.

. . . The smaller the contact patch, the lighter your touch can be, and still reliably trigger the rig.

So a spherical-to-spherical contact, or a flat-to-spherical contact, gives you more reliable triggering than a flat-to-flat contact.

If you were running a rig where the contacts had to carry substantial current, you _might_ want a larger contact surface.   But those rigs are very, very old.

.          charles
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W9KDX
Member

Posts: 770




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« Reply #6 on: February 14, 2013, 05:39:57 PM »

You _want_ them to be slightly rounded!

The logic:

. . . It takes a certain minimum pressure (pounds _per square inch) to get reliable, low-resistance
. . . connection between the contacts.

. . . The smaller the contact patch, the lighter your touch can be, and still reliably trigger the rig.

So a spherical-to-spherical contact, or a flat-to-spherical contact, gives you more reliable triggering than a flat-to-flat contact.

If you were running a rig where the contacts had to carry substantial current, you _might_ want a larger contact surface.   But those rigs are very, very old.

.          charles

Thanks, I was going by what I remembered from many years ago.  As the rounding clearly is on purpose, I figured it was a good thing.
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Sam
W9KDX
W5LZ
Member

Posts: 477




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« Reply #7 on: February 17, 2013, 09:57:39 AM »

The size and shape of contacts on keys are what they are because of how things used to be.  The voltage/current on those contacts with the 'old' equipment could be really 'large'.  So, the contacts were shaped to accommodate those higher V's and A's.  Modern equipment very seldom (if ever) has high V's and A's at the key.  So, the contacts can be almost any size/shape as long as they make reliable contact.  Those old 'dime' size silver contacts really aren't a necessity, just a 'carry-over' from days of 'yore'.  If you feel better with rounded contacts then good.  If you feel better with 'flat' contacts, file those rounded ones down flat.  Of course, then you have to readjust everything to keep those contacts making good contact.  If it ain't one thing, it's another...
 - 'Doc
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