SY4307A

SY4307A

Standard Telephones and Cables brand Australian Pentode, type SY4307A, c1940
Classification: Power Output Pentode
Service: Class C amplifier, (Radio Frequency)
Cathode
Cathode type: Directly heated
Filament voltage: 6.3v
Filament current: 1.16A
Socket connections

American 5 Pin, (UX5)
with side locating pin between pis 1 and 2.
Pin 1, Heater/Cathode
Pin 2, Screen Grid, g2
Pin-3, Control Grid, g1
Pin-4, Supressor Grid
Pin-5, Heater/Cathode

Top Cap, Anode/Plate

The type SY4307A is a power output pentode possessing a similar power rating, but significantly different characteristics to the far more common type 807 thermionic valve/vacuum tube.

Uses

Although the 807 is used for both audio amplification, (usually class AB, and radio frequency amplification in the 1-30 MHz range, (usually class C), this type was usually used for the latter.
This tube/valve is a pentode with a 'directly heated cathode', meaning that the cathode consists of an emissive oxide coated filament. These features suggest the SY4307A could predate and is contemporary with, the 807 which is a beam power tetrode, a more advanced design with a more linear transfer characteristic and a more complex 'indirectly heated cathode'.

Similarity to 807

If the pinout of the SY4307A is compared to that of the 807 the similarity is striking. All pins are assigned equivalent electrodes with the exception of pin 4, which is the suppressor grid, g3, in this type but in the 807 pin 4 is the connected to equivalent of a suppressor grid, the 'beam plates' and also the separate indirectly heated cathode. It is possible to interchange the two with the relatively minor alteration involving the linking of pins 4 and 5 and ensuring the heater supply is floating (not connected to other heaters). If the heater is supplied from an A.C. source, linking pin 4 to the centre of that source and the cathode bootstrap minimizes hum pickup.

Historical significance

The SY4307A was used extensively during World War II by the Australian armed forces and the example depicted is marked on the Bakelite collar of its base with the "D broad arrow D" commonwealth department of defense mark.
Two SY4307As were used, wired in parallel, as the output stage, or "final", in a transmitter constructed clandestinely by the Australian soldiers of Sparrow Force in Japanese occupied Portuguese Timor in 1942. This transmitter became known affectionately as "Winnie the War Winner", named after the British wartime Prime Minister, Winston Churchill.

See also

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