[Penthode]

My attempt at the transformer repair was unsuccessful. I was able to find the broken winding submerged within the transformer. The break unfortunately was between the primary and first secondary buried deep within.

So I am looking for alternatives. The transformer in my set was a light silver colored cadmium plated box which I understood to be a later replacement. When restoring the set, it was obvious that it had been replaced in the past.

I remain weary of replacing the transformer with an even later replacement and am now looking for alternatives. I was told John Folsom had a bunch of transformers rewound in 2005?. I looked at his previous posts and the last one was dated 2016. Is he still on this forum?

It is fortunate I live only about 15miles away from the Hammond Transformer Factory in Guelph Ontario. I have measured the primary and secondary wire with a micrometer and determined the primary is AWG #40 and the secondary AWG #42. From the winding resistances and with the help of a wire gauge table, estimated the number of primary and secondary winding turns. I have attached my finding and would welcome any questions about my calculations.

In addition, I have been examining an electronic alternative to the bulky transformer. I have made a conceptualized drawing which is attached. The basis of the design I shall layout below:

The vertical 60Hz parabola signal which has been generated by the 12AU7 I would estimate is 30 volts p-p. (I haven't measured it yet and if someone has put a scope probe to the plate connection of the 12AU7 feeding the transformer and can tell me what it is, I would be most grateful). The transformer with the estimated 11:1 step up ratio suggests the amplitude across the secondary winding total is 330v p-p. This is suggest is a maximum because I would expect the dynamic convergence correction amplitude to be less than this.

Because the B supply is 400 volts DC, it appears reasonable that with an amplifier with a voltage gain of 11 I should be able to linearly amplify the parabola. Instead of transformer coupling, it should be possible to capacitively couple to the high voltage convergence and focus feeds. The amplifier is driving a very high impedance load since the focus and convergence electrodes draw no current. Therefore instead of a split inductance, I can use a resistive divider to feed the convergence electrode with the higher amplitude parabola and the focus electrode the lower amplitude. (The parabola feed to the convergence electrode is the correct for dynamic convergence errors away from the center of the screen and the lower amplitude parabola is to compensate for edge of screen focus errors due to the sweep arc across a flat display panel within the CRT).

A high voltage capacitor will couple the output of the addition FET amplifier stage to the focus circuit high voltage path where the vertical parabola with added horizontal parabola effectively modulates slightly the focus voltage to improve the edge of screen or display focus. The vertical parabola is capacitively coupled to the Convergence electrode where too a horizontal parabola is added.

I am aiming to use a power MOSFET and believe I should be able to achieve the gain. Again comments welcome.