EF50 / VR91 / VR91A / 63SPT / ARP35 / CV1091 / VT250 / 10E/92 / 10E/92b / 10E/287 HF pentode
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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.
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.
Cossor 63SPT
Mullard CV1091
ARP35
VT250
In addition to the above logos, this valve also has:
SC
95
A
marked on the side, and on the end of its box.
Sylvania VR91, above, and VR91A below
Rogers VR91 / 10E/92