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This job is almost done!
As to the vertical linearity problem, I've got it figured out.
My set was a hybrid of the Rider's (early) and Sam's (later)
schematics. It had the Rider's vertical linearity fix in it.
This is a feedback circuit with two 0.0015 uF capacitors and
a 1.2 meg resistor in the vertical. Rider's says to adjust the
resistor for best linearity. This didn't work in my set. I removed
the three parts and found out why: the capacitors were very low,
well below 0.001 uF. The idea is that this circuit has a time
constant that generates a nonlinearity in the vertical sweep feeding one of the two plates that cancels the nonlinearity caused by the too-low
value of the 0.005 uF coupling capacitors going to the CRT plates.
Of course this results in a one plate having a waveform different from the other.
I tried the Rider's feedback circuit, which is a simple 5.6 Meg resistor.
This made the nonlinearity worse ... but the two sweep signals
at the vertical output plates are now absolutely beautifully linear. So
I tried adding .005 3 kV caps to the coupling capacitors to the CRT,
adding up to 0.02 uF, and now its a perfectly linear sweep. I've ordered four
0.01 uF 6 kV caps ($4 each!) from Mouser and when they are installed I hopefully
will be finished.
If you work on one of these keep these facts in mind.
Doug McDonald
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