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!