Message-ID: <15208.200103151208@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Thu, 15 Mar 2001 12:12:53 +0000
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Subject: Re: LF: VR136 = EF50?
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Dear Dick, LF Group,

Not much to do with LF I know, but the very interesting book 
"Metres to Microwaves" by E.B. Callick has a lot of info on British 
valve development in the WWII period, including many detailed 
drawings and tables. Obviously, it is mainly about the VHF - 
microwave spectrum.

The EF50 gets a mention; it was used a lot as an IF amp. The RL7 
was a development of the EF50 with aligned grids to reduce 
partition noise, and was developed for use in VHF radar RX front 
ends, where it was used as an improved replacement for the 
difficult-to-manufacture "acorn" valves. Later, it was re-designated 
the EF54.

The EF50 was, in spite of it's external metal can, one of the first 
"all glass" valves, in which the base was an integral part of the 
envelope. This meant the electrodes could be mounted directly on 
the base pins, which greatly reduced parasitic inductance 
compared to valves with a pinch seal for the lead-out wires. It also 
had relatively high transconductance. These features greatly 
improved high frequency and wide band performance. By the end 
of the war, minature B7G all-glass valves of american origin, such 
as the 6AK5, were making the much bigger EF50 obsolete.  

Cheers, Jim Moritz
73 de M0BMU