UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - PYE TT1

FERNSEH · 7th Jan 2016, 5:45 pm

The frame oscillator is of the blocking oscillator type. Transformer feedback is between the emitter and base of V25, an OC72 transistor.
The collector of V25 is supplied from -60volts which originates from the collector of the line output transistor.
Obviously without the -60 volt supply the frame oscillator will not work, but by momentarily short circuiting the frame hold control to ground the oscillator can be kicked into action. About 0.5V P - P sawtooth waveform is present across the ramp forming capacitors C74 and C75. Ref to post #7 for the circuit.
The frame output stage is working OK.

DFWB.

7th Jan 2016, 5:45 pm	#21
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: PYE TT1 - First Transistor Portable UK TV The frame oscillator is of the blocking oscillator type. Transformer feedback is between the emitter and base of V25, an OC72 transistor. The collector of V25 is supplied from -60volts which originates from the collector of the line output transistor. Obviously without the -60 volt supply the frame oscillator will not work, but by momentarily short circuiting the frame hold control to ground the oscillator can be kicked into action. About 0.5V P - P sawtooth waveform is present across the ramp forming capacitors C74 and C75. Ref to post #7 for the circuit. The frame output stage is working OK. DFWB.