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Heatercathodeshort · 18th Jun 2019, 7:57 pm

The EF91 was not internally screened requiring fiddly external metal screens in TV RF/IF strips. Fantastic valve but they also ran very hot and in the confined space of receiver units, frequency drift could be a problem, the HMV 1807 is a case in mind. [Z77s]

The EF91 with it's blue internals was the most reliable of the equivalents. Mazda 6F12, MOV Z77. Brimar 6AM6/8D3 and the Cossor SP6. There are probably more! J.

Sorry, clashed with Lawrence.

18th Jun 2019, 7:57 pm	#11
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: EF91 to EF80 The EF91 was not internally screened requiring fiddly external metal screens in TV RF/IF strips. Fantastic valve but they also ran very hot and in the confined space of receiver units, frequency drift could be a problem, the HMV 1807 is a case in mind. [Z77s] The EF91 with it's blue internals was the most reliable of the equivalents. Mazda 6F12, MOV Z77. Brimar 6AM6/8D3 and the Cossor SP6. There are probably more! J. Sorry, clashed with Lawrence.