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Aitch-Tee 20 on the air




 
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September 26, 2023, 12:17:41 PM *
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k4kyv
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Don
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« Reply #25 on: February 02, 2011, 04:56:07 PM »

It's also a matter of making things more complicated than they need to be. Proper design would ensure that a human could torque down a single-slotted set screw (or set screws) with a flat blade screw driver and the shaft would turn without slipping.

The first step in the proper direction would be to use a fine thread on an adequately sized set screw.  6-40 or 8-40 maybe on larger knobs. A torx head would work great.  They don't self-destruct with excessive torque the way allens and bristos do. I have never busted one trying to turn it, but I did break a driver once.  The splines remained intact, but the shank at the end of the driver couldn't take the torque and literally shattered to bits.  When a screw is stuck, I have found PB Blaster to be a big help.  Works much better than WD-40 or Liquid Wrench, but stinks like hell.

Another thing that sucks about allens and bristos is that the driver blade is sometimes left with a permanent twist after you try to turn a stuck screw. I've had that to happen to both the short L-shaped drivers and good quality Xcelite drivers with a plastic handle.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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KM1H
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« Reply #26 on: February 02, 2011, 09:17:21 PM »

With 2 set screws on that HT-20 Id suspect its time to measure the torque on the Cardwell (Im guessing but its Cardwell in the HT-90) cap.

And if you get tired of tightening drive it up here some Nearfest.
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w3jn
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« Reply #27 on: February 03, 2011, 06:38:03 AM »

The tuning knob drives a gear assembly that turns the tuning dial, a roller inductor, and variable cap all in tandem.  I did lubricate the shaft bearings on everything the best I could and it's much better, but I have my fingers crossed that the setscrews will stay put this time.
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W3DBB
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« Reply #28 on: February 03, 2011, 09:08:16 AM »

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Doug

beautiful downtown Strodes Mills, Pennsylvania
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