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Old 29th Jan 2016, 1:19 pm   #33
FERNSEH
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Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Default Re: PYE TT1 - First Transistor Portable UK TV

The EHT voltage is down a bit, it's about 7KV. The service manual states it should be 9 to 9.5KV. Even that is a low figure for a 14" CRT.
The auxiliary supply voltages are present and are close to the correct figures. The video amplifier HT is -63V, this is supplied through an OA81 diode which is connected directly to the collector of the line output transistor.
The negative CRT brightness control voltage is 43V, should be 53V. Again supplied from the collector of the line OP transistor.
The first anode supply for the CRT is +285V, it comes from a tapping on the EHT winding. An early silicon diode is used, type FST1/A.
The CRT is grid modulated which means the video waveform is positive going. The brightness is controlled by varying the tube's cathode voltage.
There is no modulation present at the grid of the CRT. It's possible the video output transistor has failed. It's a Newmarket PNP type V15/20R.

DFWB.
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