western electric loudspeaking loud speak peanut 4215 4215-A vintage radio wireless detector variometer museum vintage headphones
This is the "Weconomy" 3 Valve Loud Speaking Amplifier model 44013 manufactured in the UK by the Western Electric Co. Ltd. in 1923. It bears the BBC/PMG stamp and is marked with the GPO Reg. No. 3423.
The instrument is housed in a solid mahogany cabinet and is manufactured to the highest quality. Below are some more views of the amplifier:
|Interior and terminals||BBC mark||Grid bias battery clips|
click on pictures to see larger versions
The circuit diagram is reproduced below:
The amplifier is transformer coupled throughout and makes use of the miniature Western Electric type 4215-A 'Wecovalves' (otherwise know as 'peanut' valves). It's not too easy to see from this diagram how the circuit works. Redrawing reveals a novel technique that the designer used to overcome the limited current drive available from just one 4215-A valve. The 2nd and 3rd valves are in fact working in parallel to drive the primary of the output transformer. High positive excursions on the grids will demand relatively high levels of peak anode current. The 2nd valve is biased more negatively than the 3rd and so can assist the 3rd valve in delivering this high peak current demand. A centre-tapped 3V battery and single 1.5V cell are housed within the cabinet, fitted to the clips shown above. Control of the output volume is achieved by means of a tapped secondary to the input transformer. The photograph below shows the elaborate rotary switch that provides the tap selection. Also shown is the heater on-off switch, referred to as 'FIL KEY' in the circuit shown above.
click on picture to see larger version
Copyright Ó 2004 Lorne Clark