The osc. freq. is 20 kc/s. (approx.): higher than conventional T.V. line timebase, (15,625 kc/s) but comparable.
When V501 turns off relatively quickly by its grid going substantially -ve, a narrow but a large +ve pulse appears at the anode of V501 on account of the back e.m.f. from the L/C cct. in the anode cct. of V501. A substantial proportion of pulse is fed through that 22 pF to boost the -ve rails shown in the top part of the cct. diag. Doing that reduces the size of the winding that would otherwise be necessary to produce the same amount of that -ve. voltage. Again, all very similar to a valve T.V. line O/P stage, except here we don't have the additional complications of the line scan coils, linearity correction cct., etc.
The actual final EHT generation will be the usual 8.5 kV. input to a 2 or 3 diode / capacitor Walton-Cockroft voltage multiplier, commonly known as a 'doubler' or 'tripler', depending on the particular rectification scheme that has been chosen. (I suspect a doubler is used, producing a final EHT of about 15 kV.; 25 kV from a tripler seems a bit excessive for this 'scope).
Of course, there is a certain amount of guesswork involved in some of that, since we can't see the rest of the cctry. that is connected to that EHT generator cct., but I think my overall analysis is fairly close.
Al.
When V501 turns off relatively quickly by its grid going substantially -ve, a narrow but a large +ve pulse appears at the anode of V501 on account of the back e.m.f. from the L/C cct. in the anode cct. of V501. A substantial proportion of pulse is fed through that 22 pF to boost the -ve rails shown in the top part of the cct. diag. Doing that reduces the size of the winding that would otherwise be necessary to produce the same amount of that -ve. voltage. Again, all very similar to a valve T.V. line O/P stage, except here we don't have the additional complications of the line scan coils, linearity correction cct., etc.
The actual final EHT generation will be the usual 8.5 kV. input to a 2 or 3 diode / capacitor Walton-Cockroft voltage multiplier, commonly known as a 'doubler' or 'tripler', depending on the particular rectification scheme that has been chosen. (I suspect a doubler is used, producing a final EHT of about 15 kV.; 25 kV from a tripler seems a bit excessive for this 'scope).
Of course, there is a certain amount of guesswork involved in some of that, since we can't see the rest of the cctry. that is connected to that EHT generator cct., but I think my overall analysis is fairly close.
Al.
