Ten-Tec knob repair - now with pictures

If you've ever owned a Corsair I/II, 238-series tuner, 253 tuner and who knows what else in the product line, you're undoubtedly familiar with the bar-type selector knob and its propensity to crack. The antenna tuners used them for coil-tap and antenna selection; Corsairs for the bandswitch. They loosen up over time...so we crank the set screws tighter, which remedies the condition briefly...then they loosen up again and finally break.

The design is flawed: An unsupported bearing surface opposite the direction of thrust from the set screw, and perhaps with a weaker plastic compound. The little inner circular boss splits...sometimes in two, sometimes in three. From that point onward, you're going to chuck the knob and fit a new one.

Not so fast. Grab yourself a piece of styrene or ABS rod and some JB Weld, a toothpick and the old knob.

First step is to fabricate a buttress piece from the plastic rod. Use a file and flatten about 1/2" of the rod so it fits snugly into the space between the inner boss and outer knob skirt. Not too much force should be required to insert the flatted section...just enough to force the cracked inner boss together without gaps.

Attachment 14350

Next, cut the flatted piece and insert it into the knob. It shouldn't be flush with the skirt edges - a little bit below is preferred. Extract, trim and reinsert as needed:

Attachment 14351

You can see where the cracks in the boss have been closed. Most people will quit here. I want my knobs to stay fixed, so it's on to the next step.

Use the correct size Allen wrench and back out the set screw until it's flush with the outside of the knob. Then mix up some JB Weld and carefully drizzle a bit of the stuff into the gaps between inner boss and skirt. You won't fill the voids all at once so expect to make multiple passes. Clean up any overruns or spills as you go - use the toothpick or a Q-tip. Don't allow the JB Weld to begin to harden on places where you don't want it to be.

JB Weld is very viscous and even though the hardening reaction is exothermic - resulting in slightly easier flow - the mixed compound needs a little help in penetrating the nooks and crannies of the knob. So...support the bars by grasping them firmly between thumb and forefinger of one hand - boss side facing up - and using the forefinger of your other hand to repeatedly tap the knob face/insert area. You can also tap the knob on a tabletop or other non marring surface...whatever works. The idea is to simulate the actions of a concrete setting tool without actually putting anything in the JB Weld. That gets messy.

Attachment 14352

Here, you can see the partially finished work. I added more JB Weld after taking this picture, slowly building the level up to "flush" with the outer skirt.

Once you've got the JB Weld to the desired level, wait until it begins to "sag" then give everything a finish wipe and clean and set the knob aside for 16h or so. There will be a little settling as the stuff cures, and you can clean up any overlooked runs or splotches as long as it's still liquid.

After full curing is attained, place knob back on shaft and secure with set screw. If done properly you'll break the radio before you break this repair.

Nice repair guide for the onubtanian knobs ;)

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Originally Posted by PA5COR

Nice repair guide for the onubtanian knobs ;)

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Sadly, I think we're on our own when it comes to sourcing T-T parts these days. As I find parts or solutions which will work for replacement or repair I'll post them. The Sevierville gear is too nice to let go by the wayside for a lack of spares.

Nice! I have some old Hallicrafters that I can use the same fix on, thanks for the pix and instructions. I think we should officially call it the YX repair method!