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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 22nd Jan 2022, 12:16 pm   #101
FERNSEH
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Default Re: HMV 1920 made in 1960.

It's three weeks since the CRT was boosted and the tube is still displaying a bright picture but other faults will need dealing with. The worst fault is the bad interlace, line pairing is bad enough but at certain times there is no interlace whatsoever. There is no interlace filter circuit employed in this set. The frame pulses from the sync separator anode are supplied to the oscillator by a 25pF capacitor. Instead of the usual integrator circuit the eight 40uS frame sync pulses are differentiated and the negative going leading edge used to synchronise the oscillator.
A similar circuit arrangement was used in the Philips 17TG100U and RGD Deep17, these sets always display a well interlaced picture.
The application of a differentiator circuit to create the frame sync pulse was discussed in one of the Spreadbury books.
A 23" CRT was announced in America in 1959. The attachment shows an advertisement dated September 1959 for an Admiral TV set.

DFWB.
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Old 22nd Jan 2022, 1:45 pm   #102
Heatercathodeshort
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Default Re: HMV 1920 made in 1960.

We were a bit late introducing the bonded tube. To be honest it was an awkward beast, very heavy but was the first attempt at keeping the screen area dust free.
Probably the best versions were the Mullard AW47-10 and the 23" version AW59-10 that appear in the Mullard data book for 62/63. I believe Brimar/STC also introduced an early one. John.
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Old 22nd Jan 2022, 2:39 pm   #103
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Default Re: HMV 1920 made in 1960.

Could your line pairing and interlace issues be interaction between the line and frame scanning coils like on some KB models?
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Old 22nd Jan 2022, 3:12 pm   #104
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Default Re: HMV 1920 made in 1960.

There is something odd here. The 600 series had excellent interlace over the whole range of the frame hold control as did all Thorn models. I think they used the same design of scan coils from the 500 series to the 1400/1500. This may be a leaky P/C board type of fault. No doubt David will sort it and let us know the answer. John.
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