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FERNSEH · 19th Feb 2018, 1:57 pm

UKCol wrote: "Was adjusting the focus by electromagnetic means common in early sets David?"
The first generation EMI TVs employed an electrostatic focus CRT, the gun assembly was complex in it's design and construction. The later models such as the HMV 904 and Marconi 706 of 1938 employed a simple triode gun CRT with a focus coil.
The infamous HMV 1807 of 1949 used a permanent magnet focus magnet and final adjustment of the focus was achieved by altering the EHT voltage.
Whereas the HMV 1804 was an over engineered monster the 1807 chassis was made as cheaply as possible. The cabinet wasn't though, it was made to the usual EMI high standard of construction quality.

DFWB.

19th Feb 2018, 1:57 pm	#153
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: HMV 1804 Television. UKCol wrote: "Was adjusting the focus by electromagnetic means common in early sets David?" The first generation EMI TVs employed an electrostatic focus CRT, the gun assembly was complex in it's design and construction. The later models such as the HMV 904 and Marconi 706 of 1938 employed a simple triode gun CRT with a focus coil. The infamous HMV 1807 of 1949 used a permanent magnet focus magnet and final adjustment of the focus was achieved by altering the EHT voltage. Whereas the HMV 1804 was an over engineered monster the 1807 chassis was made as cheaply as possible. The cabinet wasn't though, it was made to the usual EMI high standard of construction quality. DFWB.