C. This was a soft triode valve with a lime-coated platinum filament, designed by H J Round of the Marconi Company and manufactured by Edison Swan. Other valves of similar construction were the CA, LT, N, T and TN.
R type. British version of the 'French' hard vacuum triode, having a pure tungsten, bright emitter filament. This valve and many of its variants, some gas filled, were produced by most British manufacturers. Later valves with similar characteristics, were the Cossor P1 and P2 (which had arched filaments, fan shaped grids and helmet-shaped anodes), the Ediswan AR and Mullard ORA. Higher power variants of the R valve were produced for driving loudspeakers, such as the LS series of M-OV (LS5, LS5A, LS5B, LS6A & LS9B) and the PA series of Mullard.
Q. A bright emitter triode of small dimensions having widely shaped lead-outs to minimise inter-electrode capacitance. It was a high impedance valve, used primarily as a detector. Like all early Marconi valves, it was made originally by Edison Swan (Q), but after 1919 by M-OV. Amongst the first valves produced by Marconi-Osram in 1919 was the V24 which resembled the Q except that it had a lower impedance for use as an RF or low power AF amplifier. The later DEQ was a high impedance detector.
FE1. A bright emitter, four-electrode valve of similar appearance to the Q, although larger. Marconi-Osram also produced the FE2 which was a smaller version of the FE3, and the FE3 which had a four-pin base with a side screw terminal for the space-charge grid.
DER. First thoriated tungsten, dull emitter triode to go into volume production in Britain. An earlier version of this, the LT1, went into small-scale production in 1921. Valves of similar type were the Ediswan ARDE and Mullard D.3. A year or two later various dull emitter output valves appeared, such as the Ediswan PV series, the Marconi-Osram type LS5 and the Mullard DF series, eg DFA3 & DFA8.
AR.06. A dull emitter valve having a filament of the so-called 60 mA class for operation from two dry cell batteries. Similar types were the Marconi-Osram type DE3 and the Mullard type DF.ORA and BTH B5.
"Wuncell'. First oxide-coated filament valves of British design. Valves in this series included the W1, W2, W3, WR1 and WR2. The oxide coating proved to be unreliable.
PM4. First successful oxide-coated filament valves of British manufacture (but based on Philips patents and design). Within a year the PM range was extended to about eight types. Later in 1926, Cossor replaced the "Wuncell' range with their successful "point one' and "Stentor' series of valves.
KL1. First indirectly heated triode valve for AC mains operation. The KL1 was an output valve; but also introduced by Marconi-Osram about the same time was the general purpose type KH1. Owing to poor heater-cathode construction, the valves required seven Watts of heater power and were soon replaced by more efficient types.
AC/R & AC/G. Indirectly heated output and general purpose valves using the patented slip-coating process invented by E Y Robinson of Metrovick. The construction provided a long thin cathode with good thermal conduction to the internal heater, as well as good electrical insulation between the two. The heater requirements were 4 V and 1 A, which set a standard used by all British manufacturers for many years to come.
S625. Designed by H J Round (of the Marconi Company), this was the first British screened grid valve. It had a 6 V thoriated tungsten filament. Within a short time screened grid valves became available from all the leading British manufacturers, the most popular had 2 V oxide-coated filaments.
PM22 & PM24. First British Pentode valves, both for use in the output stage of audio amplifiers. The valves were first produced by the parent company, Philips, in Holland.
PX4. Directly heated output triode for AC mains operation. Also Cossor 600T, Mazda P650, Marconi-Osram LS6A and Mullard AC044. Before this class of valve was introduced, battery types such as the M-OV P625 and Mullard PM256 were used in AC mains receivers.
SV4. Indirectly heated screened-grid valve. Also Cossor MSG41, Marconi-Osram MS4 and Mazda AC/SG.
AC/Pen. Indirectly heated output pentode. Success of the valve resulted from the use of the slip-coated cathode which enabled a high mutual conductance to be achieved without serious grid emission.
MS/PenA. First RF pentode. The valve had a low anode impedance and was little used. The main wave of RF pentodes did not appear until 1933. These included: Cossor MS/Pen, Mazda MSP4 and the Mullard SP4.
VMS4. Variable-mu screened tetrode. Also Mullard VS4, appeared in 1933.
AC/DD. Double diode for detector and AGC applications in superheterodyne receivers.
MHD4. Double diode triode. Also Ferranti HD4 and Mullard TDD4.
PM2B. Class B output valve which combined two matched triodes in a common envelope. Also Cossor 240B, Mazda PD220 and Marconi-Osram B21.
VHT4. Heptode frequency changer based on the Sylvania type 6A7.
MPT4. Also MS4B, VMS4 and MH4. A range of valves with an external anode which formed the upper part of the sealed envelope. The lower part was of glass with the pins sealed into the foot.
QP21. Quiescent push-pull output valve. Two matched pentodes in a common envelope. Also Mazda QP230 & QP240.
FC4. Octode frequency changer.
ACFC & FC2. Triode hexode frequency changers of continental manufacture. British made types did not appear until 1935-6: these included Cossor 41STH, Mazda AC/TH1, Marconi-Osram X31 & X41, and Mullard TH4, TH13 and TH13C.
AC/TP & TP22. Triode pentode frequency changers. Also Mullard TP4.
H11 & L11. Two miniature triode valves for use in deaf aid amplifiers.
HA1. Acorn triode based on RCA design. Also Mullard AT4 (triode) and AP4 (pentode).
TSP4. RF pentode, having a high mutual conductance, designed for use in television receivers.
TV4. "Magic-Eye' tuning indicator.
D1. Miniature, low capacitance diode for use as a vision detector in television receivers.
KT66. Beam output tetrode. Of similar characteristics to the RCA 6L6 which first appeared in 1936. The KT66 previously had the type reference N66. Also introduced by Marconi-Osram about the same time was the N63, whose reference was changed to KT63.
EE50. Secondary emission pentode. A valve of high mutual conductance for use in television RF amplifiers. The valve was of "all-glass' construction with the pins sealed directly through the foot.
EF50. RF pentode of high mutual conductance for use in television RF amplifiers. It had "all-glass' construction.