Tuesday, January 4, 2022

Meanwhile, Back On The Workbench....

 Work continues on the Heathkit THD Analyzer. I received the rest of the needed parts yesterday, including some pieces of 1/4" Delrin rod. The Delrin is to replace a Plexiglas insulating shaft used on a tuning capacitor. Heathkit was very fond of using this plastic to make little couplings, bushings, and insulators from, but it doesn't hold up well "Over The Ages". It gets brittle, develops cracks, and eventually disintegrates, as seen below:

The "stub" on the left end should be about three times as long to engage the reduction drive for the capacitor, and the cloudy area on the right end is where the plastic cracked and split under the load from the single setscrew that held it to the capacitor shaft. Since these parts are unobtainium, I had to make one using an aluminum 1/4" shaft coupler and a small length of the Delrin rod.

This is the reduction drive, a small ball-bearing unit made in England since King Arthur's days. I remember using these back in the 1960's, and was always kind of fond of them.

And this is the fabricated replacement for the broken plastic coupling from Heathkit:

All installed and aligned:

As far as the regulators go, here's my breadboard version, built using "ugly construction" practices to see how well my resistor calculations turned out. The small IC to the left is the original regulator, and I'll connect the new ones to the holes in the circuit board where this little guy used to live.

So now that the reduction drive for the tuning capacitor is squared away, and my prototype 24VDC regulator puts out 24.2VDC, I can get back to building up and installing the two new regulators, and continue on with bringing this analyzer back to working condition....I hope!


  1. Small steps, big rewards to come!

    1. Yeah, but I get creepy feelings whenever a piece of gear I'm reconditioning fails at step 3 of the checkout, before you even get to the calibration routine!

      I wonder what other gremlins lurk beneath the surface....?

  2. in the olden days of my electronics technician career, I would go to the "lab craftsman" for those mechanical chores. We were lucky enough to have one of the best-in-class guys, "Bruce," who was available for those custom needs. You, on the other hand, probably wouldn't need a craftsman since you seem to have those skills as well.

    1. I've always been pretty good at both Electronic and Mechanical things. Got some of the skills homebrewing Ham gear, and the rest at the various jobs I've held. I was the Go To Guy in my Department at Hughes for little things like this.

      With 50+ years of experience, it's easy to spot where Heath saved a few $$ on parts, at the expense of long term durability.


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