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Radio Valves

Valves from before WWII

Pre-history: Before valves

A number of devices were made during the 19th.Century that developed the technologies that enabled and, to some extent, prompted, the invention of thermionic valves.

Experimental incandescent lamps with platinum filaments in a vacuum were developed by 1840. Frederic Guthrie discovered the loss of charge from heated bodies in 1873. Swan and Edison both patented commercial lamps in 1878. On February 13, 1880 Edison rediscovered thermionic emission and made experiments to show conduction between the filament and a second electrode in the envelope of an incandescent lamp. He patented the use of this device as a voltage regulator.

X-Ray Tube
X-Ray Tube

ca. 1905

Other electron devices that preceded valves included the Crookes tube (1875), used to study conduction in low pressure gases, and X-ray tubes. Crookes tubes operate at high voltages (at least several kV) and ionisation of the gas produces free electrons which strike the anode with sufficient energy to produce X-ray photons. These were first systematically investigated by Wilhelm Röntgen in 1895.


Valves before 1919

Royal Edison Oscillation Valve
Royal Edison Oscillation Valve

before 1910

The Fleming Oscillation valve

Fleming discovered the rectification of the Edison device and patented its use to detect radio waves in 1904. This was a simple diode with either a carbon or tungsten filament. The one shown at left was a commercial version, probably made before 1910.

Soft valves

On February 18th., 1908, Lee DeForest patented the three electrode Audion. De Forest himself admitted that he had no idea how it worked, but did specify that it should contain gas at low pressure. This was the first device that used a third electrode between the filament and the anode to control the current in the valve. This was not a true vacuum tube. Early Audions were very unrelaible due the the gas filling being adsorbed onto the internal walls and metal components.

Many other investigators, including H.J. Round, of Marconi, G.W. White, at the Cavendish Laboratory,and Lieben, Reisz and Strauss at Telefunken developed these devices and improved the reliability, mostly by adding facilities to allow the gas pressure in the valve to be restored to the correct working level. Round's valves had a tube attached, filled with asbestos fibres. When this was heated, with a match, gas was evolved and the function of the tube restored. White's 1916 valve contained mercury vapour and had an oxide cathode. It was put into service with the Royal Navy but proved to be erratic in service.

Hard Vacuum Valves

Pliotron
Langmuir's Pliotron

April 5th., 1915
Pliotron
Typical electrode construction of
a German WWI valve

French TM valve
French TM valve

1915

Dr. Irving Langmuir, working for the General Electric Company, developed a hard vacuum triode, which he patented in April 1915. He had earlier developed improved diffusion pumps, to produce harder vacuums and from 1913 developed his Pliotron, along with a hard vacuum diode, the Kenotron.

The French TM valve was developed from the pliotron. It was the mainstay of radio communication during the first World War and the basis of all the later bright emitter triodes until the early twenties.Most French examples had ungettered spherical envelopes with tubular anodes, spiral grids and straight pure tungsten filaments. British made 'R' types were more varied and included tubular envelopes and various gettering.

German valves of this period used a very primitive electrode structure, which resulted in valves which could only be used for low frequency amplification. In late 1917 they began to make copies of captured TM or R type valves.


Here is a timeline of the development of valve manufacture in the U.K. up to 1930.


Early Transmitting Valves

Marconi rectifier
Marconi MR1 rectifier

as used in the 2MT transmitter in 1920
Mullard 2.5 kW valve
Mullard 2.5 kW transmitting valve

possibly N.T.22, 1921


Triode valves from the dawn of Broadcasting 1920-25

Bright Emitters

"Brights" used pure tungsten filaments and were operated at 2500-2600 K. This is somewhat brighter and whiter than a modern incandescent bulb. All these designs were more or less the same as the 'R' types that were used during the first World War. Filament power was typically 2-3 W (4V and 0.75A). Cold filament resistances of less than 0.5Ω are diagnostic of bright emitters. Gain (μ) was between 6 and 9 when operated at 30 - 80 anode volts.

R type
'R' type

Radions
1917?
P1
P1

A.C. Cossor
1922
P1
P1

A.C. Cossor
1923?
R5v
R5v

M.O. Valve Co.
1922/3
AR
AR

Edison-Swann
1922/3
LF-GR
LF 'Green Ring'

Mullard
1923/4
Radio Micro
No type markings

Radio Micro
1923?

Dull Emitters

Dull emitters use a thoriated tungsten filament operated at 1700 - 1900 Kelvins. These gradually replaced bright emitters in domestic receivers in the period from 1922-5.The thoriated tungsten filament was much more efficient, consuming less than a watt. This reduced 'A' battery drain to one or a few hundred milliamps, extending accumulator life between charges by a factor of 5 to 10.

B5
B5

BTH
1923?
ARDE
ARDE HF

Edison-Swann
1922/3
6\100Amp
6\100Amp

Lampe Metal
1923?
Radio Micro
No type

Radio Micro
1924
Radio Micro
No type markings

Radio Micro
1923?
Radio Micro
'Spècial'

Radio Micro
1924/5?
DE4
DE4

M.O. Valve Co.
1924?
CT25
CT25

Cleartron
1925
DE5A
DE5A

Marconi
1925/6

Oxide Cathodes

A.C. Cossor in the U.K. and Western Electric in the U.S. both solved the problem of producing a filament coated with alkali metal oxides that was robust enough for prolonged everyday use, before 1925. These were operated at 900-1000 Kelvins, a dull red heat.

WR1
WR1

A.C. Cossor
1925
W3
W3

A.C. Cossor
1925
4215AB
4215AB Wecovalve

Western Electric
1924

Data for these valves was apparently not published but I have found some heater data which may be of use to those wishing to "light up" one of these valves. There is a characteristic curve on the B5 page.


Battery Triodes from 1925-40

Mullard

Philips had invented the 'Azide' process which increased the emission of dull emitter cathodes beyond that obtainable from thoriated tungsten. This process produced an oxide covered cathode which was more robust and long lasting than other competing methods, for example the A.C. Cossor 'Wuncell' type. Before assembly the tungsten filament was directly oxidised or plated with copper and oxidised. The anode was coated with barium nitride (Azide). After evacuation the anode was heated (probably by induction) and the evaporated barium nitride reduced the oxide on the filament forming barium oxide, metallic tungsten or copper and nitrogen which was adsorbed by the getter.

Mullard commenced production of these P.M. (Philips Mullard) valves in 1925 with the PM3 and PM4.

PM1A
PM1A
PM1HF
PM1HF
PM1HL
PM1HL
PM1LF
PM1LF
PM2
PM2
./PM254/PM254
PM254
./PM256/PM256
PM256
./PM2DX/PM2DX
PM2DX
./PM2HL/PM2HL
PM2HL
PM3
PM3
PM4DX
PM4DX
PM5X
PM5X
PM6
PM6

A.C. Cossor

Cossor had earlier perfected a process for oxide coating filaments. A new process enable them to reduce the filament current to 100mA for their Point One series of valves.

LF
LF

Cossor
stentor2
Stentor 2

Cossor
210DET
210DET

Cossor
210HL
210HL

Cossor
210RC
210RC

Cossor
215P
215P

Cossor
220P
220P

Cossor

Marconi-Osram

B21
B21

Osram
DEL210
DEL210

Marconi
H2
H2

Marconi
H210
H210

Marconi
LP2
LP2

Osram
PX4
PX4

Osram
VT50
VT50

G.E.C.

Triotron

Triotron manufactured valves in Austria, the valves were imported into the U.K, and achieved significant market share as they were cheaper than those made by the B.V.A. cartel. The earlier ones appear to be 'Azide process'like the Mullard 'PM' series above, judging by the dark speckled deposits on the envelopes.

AN4
AN4

Triotron
TD2
TD2

Triotron
ZD2
ZD2

Triotron

Tungsram

Tungsram valves were manufactured in Hungary, by a long established electric lamp maker, who had patented the tungsten filament in 1903. The name is a contraction of TUNGsten and wolfRAM. Large numbers were imported into the U.K. Like Triotron they achieved significant market share by undecutting the B.V.A. cartel. Again these were 'Barium' valves and may have been produced by the 'Azide process'.

LG210
LG210

Tungsram
P215
P215

Tungsram
P415
P415

Tungsram
R2018
R2018

Tungsram
R208
R208

Tungsram

Other Makers

BW602
BW602

Unis
K30K
K30K

Ever Ready
LF2
LF2

???
PX230
PX230

Hivac
SS2aLF
SS 2a LF

Six-Sixty
SS8
SS8

Six-Sixty

The PX230 and PX4 have quite heavy filament currents and although directly heated they are often used in mains equipment.

Battery Rectifier, Tetrodes, Pentode and others

A 2 volt full wave rectifier for battery eliminators and directly heated tetrodes for battery powered superhets and RF amplifiers etc. The QP21 is a double pentode for quiescent push-pull (Class B) audio amplification.

215SG
215SG

Cossor
451
E451

Philips
K80B
K80B

EverReady (Mullard)
KT2
KT2

Marconi
PM12
PM12

Mullard
PM22
PM22

Mullard
PM24A
PM24A

Mullard
SS8
PT2

Marconi
QP21
QP21

Marconi
TP22
TP22

Mazda

Mains Valves

Valves for use in mains powered receivers etc. Mostly indirectly heated, with 4 volt 1 amp heaters. The S130 is a cold cathode voltage regulator.

2D13
2D13
354V
354V
41MPG
41MPG
AC2/PEN
AC2/PEN
ACHL
AC/HL
ACSG
AC/SG
catkin
catkin
FC4
FC4
IW4-500
IW4-500
MPT4
MPT4
MS4B
MS4B
MS-PEN
MS-PEN
MVSG
MVSG
S4V
S4V
S4VA
S4VA
S130
S130
VHT4
VHT4
VPT4B
VPT4B

© Andy Cowley, 2005-2012        Home