Improving old TV sets.

[Geordie McBoyne]

"I did wonder about messing with the line oscillator to improve its linearity but haven't done it.," Hi Peter, I intend to fit a timebase switch to my Marconi 702.   As well as changing the repetition rate of the blocking oscillator the switch introduces an additional ramp forming capacitor C3.  On 25c/s scanning C4 would be fully charged before the end of the frame scan, so C3 in introduced so that the sawtooth waveform will be as linear as possible.   These may be ancient circuits, it's likely design work started on these sets in 1935, but the circuit diagram shows that a great deal of attention was taken to produce a linear scan.
Note that the bottom end of the ramp forming capacitors are returned to the output valve cathode and scan coils.

Till Eulenspiegel.