[Penthode]

After a couple of months hiatus busy with other projects. I am returning to the CT100.

If you recall. my circuit worked well but there was insufficient amplitude. I gave up looking for a suitable audio transformer to step up the signal.

Looking for a more efficient and less expensive approach, I have decided to increase the B plus to the FET in order to get a greater voltage swing on the drain. There was more than enough gain as the convergence controls would drive the FET output to clip the convergence waveform parabola.

Looking at Digikey and Newark, there is a large array of 1000v plus power FETs which exhibit the linearity and provide the signal gain. To boost the drain supply I will experiment with using a standard 300mA filament transformer in reverse. I will tap into the 6.3 vac filament line to step up to 230vac and use a simple bridge rectifier. The current demand is very low which means only very simple filtering is required. A bridge rectifier will yield about 320volts DC which I will stack on top of the +400v supply.

The new diagram with the stepped up drain supply is attached.