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FERNSEH · 2nd Jun 2015, 9:31 pm

Hi Robin,
I reckon your best approach to solving the problem you have with the Derwent TV will be to rewire the line timebase circuit to the specification of the Plessey Mark 1. The circuit of the Regentone T15L in fact.
Is the chassis of Central Equipment manufacture or is it the Plessey Mark 1? The latter is easily identified by it's RF chassis. In the Mark 1 a 0.25mfd capacitor is wired across the 1Kohm line hold control. The secondary of the line output transformer feeds the scan coils via a 100mfd capacitor the other side of the winding goes to chassis. The secondary also connects to the line hold control and the suppressor grid of the EL38 (V11) via the 100Kohm line linearity control and a 27Kohm series resistor. The screen grid volts should be 70. Your HT voltage is correct.

I hope these notes help.

DFWB.

2nd Jun 2015, 9:31 pm	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Derwent 9" television Hi Robin, I reckon your best approach to solving the problem you have with the Derwent TV will be to rewire the line timebase circuit to the specification of the Plessey Mark 1. The circuit of the Regentone T15L in fact. Is the chassis of Central Equipment manufacture or is it the Plessey Mark 1? The latter is easily identified by it's RF chassis. In the Mark 1 a 0.25mfd capacitor is wired across the 1Kohm line hold control. The secondary of the line output transformer feeds the scan coils via a 100mfd capacitor the other side of the winding goes to chassis. The secondary also connects to the line hold control and the suppressor grid of the EL38 (V11) via the 100Kohm line linearity control and a 27Kohm series resistor. The screen grid volts should be 70. Your HT voltage is correct. I hope these notes help. DFWB.