CT-100 B1001599 Failed Convergence Transformer

[old_coot88]

Cool idea with the xfmr. As a young kid, i used to use two 6V doorbell xfmrs back-to-back for isolation to make B+ for projects.

[Penthode]

Hmm. I am boosting the B+ and I see the boost B+ on the CT100 is 680v. I am going to investigate using it for the FET. Would only require at most a resistor and capacitor....

[Penthode]

Here is my latest further simplified itteration. I will grab the B+ boost from the flyback transformer. The FET will be picking off about 3mA which should be relatively inconsequential. The 650VDC available as a supply to the FET drain should allow a nearly 600v p-p swing which should be adequate to provide the vertical convergence.

See the attached drawings for the modified circuit and the B+ boost source.

[Alex KL-1]

If +Boost reduces only a little with extra load, is nothing to be worried

[Penthode]

I am currently searching for a MOSFET with Vds of minimum 1000v. In these days of switchmode power supplies, devices of 1000 volts plus abound.

The convergence waveform amplitude of max 350 p-p was so close I believe the additional B+ boost should be just enough to achieve good vertical convergence.

The circuit replacement will be more reliable and not subject to the fragile transformer leakage and failure.