CV1091

EF50 / VR91 / VR91A / 63SPT / ARP35 / CV1091 / VT250 / 10E/92 / 10E/92b / 10E/287 HF pentode

The valve measures 73x37mm and has a B9G base

The introduction of the EF50 was important as it enabled use at higher frequencies. Its construction differed from 'traditional' valves in that there were no long leads from the base pins up to the electrodes. Valves of the time had difficulty working above 30MHz due to their construction. After a lot of experimentation in the early 1930s, RCA produced the Acorn valve, the first production one of these being the 955 in 1934, then the 954 in 1935. Acorn valves were later produced in the UK but companies found them difficult to make, and thus after further research and development the EF50 was produced.

Heater voltage	6.3V
Heater current	0.3A
Max anode voltage	300V
Max screen voltage	300V
Max anode dissipation	3W
Max screen dissipation	1.7W
Mutual conductance (Va=Vg2=250V; Ia=10mA; Vg1=-2V)	6.5mA/V
Max working heater-cathode voltage	140V
Max operating frequency	125MHz
Capacitances
Cae	5.6pF
Cge	8.3pF
Cag	0.007pF

Pin	Function
1	Heater
2	Screen grid
3	Anode
4	Suppressor grid
5	Internal screen
6	Cathode
7	Control grid
8	Internal screen
9	Heater

An improved variant of the EF50 known as RL7 (VR136) was produced. This was later redesignated as EF54.

EF50

This Mullard EF50 has "MB1 B2F2" stamped on the edge of the base.

The EF50 had numerous aliases including VR91 and CV1091. However the VR91A (see below) is equivalent to a different CV number, though the data and test data are all the same so it is included here.

This Cossor EF50, also showing the 63SPT type number, has "MB1 B0H" stamped on the edge of the base.