Mike's idea will work. It is a technique most all technicians should know.
When one is out in the field and needs to get the unit in service NOW and
the proper repair tools / materials are not available then we use it. If we
are in the shop, radio shack, or garage with time to acquire the proper
tools / materials, then a decent technician would repair it in a more
permanent manner. We would also make a note to replace the 'field repair'
with a permanent and proper repair as soon as practical.
Loctite makes a product called Blue Max. It is specifically designed for
this type of problem (worn out or stripped threads). This is a quick and
simple fix (also it is reasonably permanent).
If you require more substantial threads than this product provides (I
believe Blue Max is perfect and will be strong enough for this job), than
the problem is permanently repaired by drilling, tapping and installing a
keensert or similar product. A keensert is like a bushing with threads on
both the inside and outside; you will want to ensure that the inner threads
match the threads of the setscrew. Helicoil also makes a similar
bushing-like thread insert, in addition to their 'coils'.
Keep in mind that the above solutions only fix the symptoms not the problem.
After the damage is repaired you need to fix the problem. To fix the
problem: DO NOT over-tighten the setscrew. The threads of the setscrew are
tiny, the threaded material weak and neither can withstand much torque.
Stephen AD7TD
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Tom NØJMY
Subject: Re: [TenTec] Two Century 21 problems
I'm sorry, Mike. I did a lousy job of explaining this problem. It
would have been easier if I had just said "the threaded holes in the
knobs are stripped". This is where the problem lies.
The screws turn in as they should, but then continue to turn after they
make contact with the shaft.
I am going to try Mike's suggestion of running a thin wire inside the
hole in a few minutes.
Thanks for the reply, though.
73,
Tom
Mike Hyder -N4NT- wrote:
> If the screws are going in so far that they fall out the inside of the
> knob, it sounds like a sleeve is missing or something like that.
> Compare the diameter of the rod onto which they mount with the diameter
> of the hole in the knob.
>
> Specifically, the set-screws in the main tuning knob are indeed tiny in
> diameter. I don't know their length.
>
> Mike N4NT
>
> ----- Original Message ----- From: "Tom NØJMY" <n0jmy@hayseedhamfest.com>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Friday, June 12, 2009 12:32 PM
> Subject: [TenTec] Two Century 21 problems
>
>
>> I'm going back together with the first of four Century 21's here. First
>> off, is it me, or are the set screws in the main tuning knobs really
>> tiny? Such that the threads in the knob are excruciatingly fragile? I
>> haven't got one out of the four that will tighten enough to stay secured
>> to the PTO shaft. A couple of the screws can be pushed right through.
>> Any thoughts on a simple fix for my simple mind?
>>
>> Second, and more serious. I had one up and running yesterday on 20
>> meters. Seemed to have good sensitivity, maybe even above average. So
>> I plugged in the matching calibrator which put in a deafening
>> signal...for awhile. As I tuned to zero-beat the audio quit completely.
>>
>> After monkeying around with it for about twenty minutes without plan, I
>> switched the selectivity control from narrow to the middle position and
>> pop, the audio came back. On all three bandwidths.
>>
>> So I turned the RF and AF controls way down, turned the calibrator back
>> on and started increasing the gain. Like an idiot, I can't remember
>> which one, maybe both - arrgh! The calibrator had plenty of signal all
>> the way to the top of ten meters.
>>
>> But as I continued to increase gain, poof. No audio again. It wasn't
>> near maximum gain either. And this time it hasn't come back.
>>
>> What would cause this behavior? And any ideas where I should start my
>> trouble-shooting? Being primarily a boat-anchor man, I can use all the
>> help I can get.
>>
>> Thanks,
>> Tom
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
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