CT100 Convergence Transformer Solid State Replacement Update

[Penthode]

I found the problem with the video sweep. I will mention it here as it may affect others.

While adjusting the convergence, I found the Vertical Conv. Amplitude control would not adjust linearly. So i removed the control to more closely examine. Testing with a VTVM, I saw no problem. I replaced the control and found when powering the set the vertical sweep was non linear and compressed.

Disconnecting the 0.22 uF capacitor connected to the vertical amplitude shape control I measured only 6kohm to ground. Looking at the circuit diagram, it should have measure minimum about 7 megohm. The 0.22 was shunting the output of the vertical oscillator to the vertical output grid. Moving the potentiomenter lead, the resistance jumped to anbout 7 megohm. Replaced the lead powered the chassis and the vertical output signal still compressed. Measured the vertical amp. shape pot lug to ground, the resistance was again 6 kohm!

I carefully washed and brushed with an artist's paintbrush the area around the pot connections. Problem gone.

It looks like 70 years of grime and the the high circuit impedances (around two 5 megohm pots!) caused the intermittencies. The pots looked quite clean and I was not as scrupulous as I should have been around the pot.

It was following the horizontal hold control exhibiting the same leakage problem suddenly last week. The control runs at about 200 vdc above ground and a minor leakage made the the oscillator control section of the 6SN7 to pull the horizontal oscillator off frequency. Odd as both these pot problems happened suddenly without warning.