Summary

The A409 was a general purpose triode with similar characteristics to the 201A except that its filament consumption was only about 20% of the American valve. This was made possible by the use of an oxide coated filament.
The oxide coating on the filament of this valve was produced by the so called 'Azide process'. Filaments produced in this way tended to be less robust than the thoriated filament of the 201A but the low power drain of these 'Miniwatt' valves made them very popular at the time. It had a 4 Volt directly heated cathode and was used as a class A amplifier.
Manufacturer: Philips, Holland.
The statement 'Sold for amateur use only' relates licensing of various patents. Valves sold to manufacturers would attract a licensing fee.

Physical Description

Conical bulb with 4 pin American style base.

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