21-12-2017, 09:24 PM
(This post was last modified: 21-12-2017, 09:29 PM by Geordie McBoyne.)
Hi Trevor,
The HMV continues to work very well indeed. Only the sound needs attending to. Picture interlacing could be better and the only way to achieve near perfect inlerlace is by critical adjustment of the frame hold control. The unknown engineer must have been aware of this problem because a Pye type of interlace filter module had been introduced into the circuit. The original HMV 1804 and Marconi VT50 employ a D63/6H6 double-diode as the interlace filter, but only one diode section is used. It's V8 in the EMI circuit diagram. I'm certain it would be much better to employ both diode sections and reintroduce the Pye "positive interlace filter" circuit. The attachment shows the interlace filter circuit employed in the Pilot CV34, it is very similar to the circuit which was used in the Pye FV1 series of TV receivers. Mike Barker rewound the original EHT transformer, now the EHT circuit is delivering a stable 4KV to the CRT anode. The CRT is surprisingly bright considering it is the original.
Geordie McBoyne.
The HMV continues to work very well indeed. Only the sound needs attending to. Picture interlacing could be better and the only way to achieve near perfect inlerlace is by critical adjustment of the frame hold control. The unknown engineer must have been aware of this problem because a Pye type of interlace filter module had been introduced into the circuit. The original HMV 1804 and Marconi VT50 employ a D63/6H6 double-diode as the interlace filter, but only one diode section is used. It's V8 in the EMI circuit diagram. I'm certain it would be much better to employ both diode sections and reintroduce the Pye "positive interlace filter" circuit. The attachment shows the interlace filter circuit employed in the Pilot CV34, it is very similar to the circuit which was used in the Pye FV1 series of TV receivers. Mike Barker rewound the original EHT transformer, now the EHT circuit is delivering a stable 4KV to the CRT anode. The CRT is surprisingly bright considering it is the original.
Geordie McBoyne.
