[FERNSEH]

The Pye 405 line colour set has always had bad frame linearity. The sawtooth drive to the grid of the PL82 frame valve has perfect linearity and amplitude. A series of tests have been carried out to determine if the fault lies in the secondary circuits of the frame output stage, for example the path of the sawtooth drive from the output transformer through the convergence network, no faults found. I did think I'd got lucky when the 2200uF capacitor in the vertical picture shift circuit was found to be of low capacity, replacing it made no improvement. I'm absolutely certain that scanning coils are OK. Now I have other ideas on how to solve the problem.
Talking to Mike (Mikey405) about this on going fault we consulted the circuit diagram of the Ekco round CRT colour set which was made in the early sixties.
The CT100 employs an ECL85 as the frame oscillator and output valve. What was noted is that although the screen grid of the pentode section is supplied from the 200 volt HT supply the anode is supplied from the 360 volt HT line which also supplies the line output stage. Now this begs the question: in the Pye CTV should the PL82 frame output valve also be supplied from the 360 volt supply? Both sets employ a voltage doubler to supply 360 volts to the line output stages. Examination of a 1950s CBS colour TV circuit revealed the same thing, the 6BL7GT frame output valve also receives it's HT from a much higher voltage B+ source, 400volts in the American receiver. So now the Pye CTV will be reassembled and voltage measurements carried out on the frame output stage. As far as I can remember the frame output stage receives it's supply from the 200 volt HT line.
The absolute highest voltage supplied to the anode to the PL82 is 550V, so there is no doubt the valve should with stand 350 volts or so on it's plate. Let's find out if that is so.

DFWB.