•
1st letter: Heater rating :*
A 4V AC (See Note 1) :*
B 180mA DC (See Note 1, 2) :*
C 200mA AC/DC (See Note 1) :*
D 1.4V or less (normally 1.4V) or 2.8V/1.4V series/parallel filament :*
E 6.3V, or 12.6V/6.3V series/parallel heater; usually AC :*
F 12.6V (See Note 2) :*
G Formerly 5V (often used for rectifiers) or later miscellaneous :*
H 150mA AC/DC :*
I 20V (See Note 2) :*
K 2V DC :*
L 450mA AC/DC :*
M 1.9V directly heated (See Note 2) :*
N 12.6V, indirectly heated (See Note 2) :*
O Cold cathode (by 1955 this also included
semiconductors as these had no heater) :*
P 300mA AC/DC :*
Q 2.4V indirectly heated (See Note 2) :*
S 1.9V indirectly heated (See Note 2) :*
T 7.4V (See Note 2, 3) :*
U 100mA AC/DC :*
V 50mA AC/DC :*
X 600mA AC/DC :*
Y 450mA AC/DC (replaced by
L, to allow
Y to be used for professional transmitting, microwave or industrial tubes) :*
Z Cold cathode and/or gas-filled tubes :
Notes: ::Heater ratings for series-string, AC/DC tubes are given in milliamperes; heater ratings for parallel-string tubes are given in volts ::(1) Letters
A,
B, and
C were rarely used after the 1930s and discontinued long before the 1960s and so allocated to semiconductors in the
Pro Electron naming scheme ::(2) Letters
B, F,
I,
M,
N,
Q,
S and
T were so very rarely used that most tubes beginning with these letters (such as the FC13
Octode, the function letter
C of which doesn't match anyway) should not be assumed to be part of this naming scheme. ::(3) Letter
T was introduced solely for use with the TY86F EHT rectifier. This was an EY86 with a higher voltage heater specifically manufactured as a replacement for
Ferguson television sets 306T and 308T manufactured in 1956. These produced excessive voltage from their line output circuits which rapidly destroyed the originally fitted EY86. ::The main letters used in the second half of the twentieth century for receiving tubes were:
D,
E,
G,
L,
P and
U although
X was also frequently found when 600mA heater chain versions were produced for the North American market. •
Remaining letters: Type(s) of device(s)) •
S TV sync oscillator •
T (Deflection-controlled) beam tube, or miscellaneous •
W Gas-filled halfwave
rectifier •
X Gas-filled fullwave rectifier •
Y Halfwave rectifier (power diode) •
Z Fullwave rectifier (double power diode) :* Special quality "
Z" cold cathode tubes: ::*
A Long-life amplifier tube ::*
B Binary counter or switching tube ::*
C Common-cathode
Counter Dekatron that makes only
carry/borrow cathodes separately available for cascading ::*
E Electrometer tube ::*
G Amplifier tube ::*
M Optical indicator ::*
S Separate-cathode
Counter/Selector Dekatron that makes all cathodes available on individual pins for displaying,
divide-by-n counter/timer/prescalers, etc. ::*
T Relay triode, a low-power triode
thyratron, one starter electrode, may need illumination for proper operation if not radioactively primed ::*
U Low-power tetrode thyratron, may mean: :::*One starter electrode and a primer (keep-alive) electrode for ion availability to keep the ignition voltage constant, for analog
RC timers, voltage triggers, etc., or :::*Two starter electrodes to make counters bidirectional or resettable ::*
W Trigger pentode, two starter electrodes and a primer electrode •
Numbers: Base type and serial number mostly locking bases: "9-pin Loctal" (B9G) or 8-pin Loctal (B8G); but also used for Octal and others (3-pin glass; Disk-seal; German 10-pin with spigot; min. 4-pin; B26A; Magnoval B9D) :*
60–64 All-glass valves fitted with 9-pin (
B9G) bases :*
65-69 Sub-miniature all-glass valves with or without bases :*
70–79 Loctal Lorenz an all-glass wire (fly-leads in place of pins) subminiatures :*
80–89 Noval B9A (9-pin; IEC 67-I-12a) :*
90–99 "small-button" B7G (miniature 7-pin; IEC 67-I-10a) :*
100–109 B7G; Wehrmacht base; German PTT base :*
110–119 8-pin German octal; Rimlok B8A :*
130–139 Octal :*
150–159 German 10-pin with spigot; 10-pin glass with one big pin; Octal :*
160–169 Flat wire subminiatures; 8-pin German octal :*
170–179 RFT 8-pin; RFT 11-pin all glass with one offset pin :*
180–189 Noval
B9A :*
190–199 B7G :*
200–209 Decal
B10B :*
230–239 Octal :*
270–279 RFT 11-pin all glass with one offset pin :*
280–289 Noval
B9A :*
300–399 Octal :*
400–499 Rimlok
B8A :*
500–529 Magnoval
B9D; Novar :*
600–699 Flat wire-ended :*
700–799 Round wire-ended :*
800–899 Noval
B9A :*
900–999 B7G :*
1000- Round wire-ended; special nuvistor :*
2000– Decal
B10B :*
3000- Octal :*
5000- Magnoval
B9D :*
8000- Noval
B9A :
Notes: ::For signal pentodes, an odd numerical identifier most often identified a variable transconductance (remote-cutoff) valve whereas an even number identified a 'high slope' (sharp-cutoff) valve. ::For power pentodes and triode-pentode combinations, even numbers usually indicate linear (audio power amplifier) devices while odd numbers were more suited to video signals or situations where more distortion could be tolerated.
Single-digit numbers The first types assigned using this sequence (in the mid to late 1930s) were less systematic and sometimes would append the US "G" and/or "GT" suffixes for octal base versions, although the base type was not always knowable from just the type number: • KK2 (Cap E) was a pinch-type valve fitted with an American 7-pin base. • Sometimes special versions were made with US (Ux-4 to 7) bases with no change in the type number (e.g. AF2, AK1, KK2), but • in the case of
Octal (IO) often a "G" would be appended to the type number; examples are ECH3G, ECH4G, EK2G, EK2G/GT, EL3G, EL3NG, KF3G, KK2G and KL4G. • EBF2Gm EBF2GT/G and EBF35 had International Octal bases but European base connection sequences. • Versions without the pinch at the top and/or with a metal screen might have "N" appended, and letters "A", "B" or "X" would sometimes be used for variants (e.g. AL2X, ECH33B, ECH35A, EL3N and EL3NG). The AL2X differs from the AL2 in connecting the control grid to pin 6 instead of the top cap. EL33, EL33A and EL33B are octal power pentodes differing only in whether metallization shielding is connected to pin 1 or 8. • The AL3, AL4, EL3N and EL3NG have identical characteristics to the EL33, EL33A and EL33B but with different heater voltages and/or bases; the CL4 and CL33 are lower voltage and lower power devices that are only somewhat similar to the EL33 and PL33.
Historical progression The older Philips system Prior to 1934, Phillips numbers were based on a sequence of one letter to indicate filament current range, followed by one or two digits for the filament voltage, then two digits that gave either the amplification factor (for triodes) or a code beginning with 41 to indicate tetrodes, pentodes and so on. Examples are: • A409 (a 4Volt/65mA filament triode with a mu of 9) • B2043 (a 20V/180mA
indirectly-heated power output pentode from 1931) • C243N (a 2V/200mA filament power output pentode from 1931 with the option of B5 and Ux5 bases).
Single-digit numerical sequences An example of this format is "CL4". This format was used from 1934, when many European-specific bases existed. These bases included 5- and 8-pin side-contact, and 4- to 7-pin alternatives to incompatible US base types. At this time there was pressure to produce devices compatible with wider markets, and so several versions of the same device might be produced with different bases, yet sometimes no change in type number.
Double-digit numerical sequences An example of this designation format is "EL33A". After about 1938 the digits gave a more consistent definition of the base type. During the 1950s, most often two devices that shared the same number and all but the first letter of the name would be very similar except for heater voltage/current. During this time older filament voltage and current "families" were abandoned, so a device name beginning with "A", "B", "C" or "K" and ending in two or more digits is very unlikely to be part of this naming scheme. For example, the "KT61" is not a 2 Volt-filament beam tube within the Philips naming system, but a "kinkless tetrode" within the Marconi/EMI naming scheme.
Triple-digit numerical sequences Examples of this format are "PL302" and "EF183". From about the start of the 1960s an extra digit was needed for new devices. Either a digit
1 was inserted before the
8 or other base-defining digit (e.g. an EF184 is a Noval pentode), or a three-digit sequence was used. For example, a PL500 is a power pentode in a Magnoval base.
Four-digit numerical sequences Numbering using four digits were never issued under the Mullard-Philips scheme. They were obtained from the successor scheme, Pro Electron. ==Semiconductors ==