The Louden valves were made in the UK from 1924 by the Fellows Magneto company. The F1, F2 and F3 were all bright emitters. The F1 and F3 were both for detector and AF amplification. The F2 was for RF stages and had more turns on the grid and a higher AC resistance.
This exhibit has the metal base shell and thus is one of the early batches. The clear glass support the advertising of 'Silver Clear'. Like all the Louden valves the anode is a wire helix rather than a solid cylinder.
The concentric for of the electrodes with a single strand filament that once passed through the centre of the grid in this bright emitter valve.
A closer view of the grid and anode.
The supports are anchored in the glass pinch and each electrode is held by a fold in its support. The remains of the filament can be seen in the outer supports.
Another view of the grid and anode. Note that the grid extends beyond the anode helix.
The glass looks to be without any markings but close inspection reveals the trade mark but no Type designation. This enhanced image shows tiny points of light that are the minute dust particles on the envelope.
Thanks to Derek L Widdowson for donating this exhibit.
The envelope is 46 mm in diameter, and excluding the B4 base pins is 89 mm tall.
References: 1003 Type F1 was first introduced in 1924.