The Marconiphone 55 belongs to the class of
"5 triode" portable receivers dating from the late 1920s. Two triode valves are used to provide HF amplification. Although the high inter-electrode capacities of triodes makes them unsuitable for straight amplification at HF (the feedback creates instability), by limiting the gains severely it is just about possible to make them work.
The valve line-up is:
HL210 First HF amplifier
HL210 Second HF amplifier
H210 Leaky grid detector
L210 AF amplifier
Capacitative reaction is employed, and transformers are used for AF coupling between the detector, AF amplifier and output valves. The set is mounted on a turntable, and an internal frame aerial is used, tuning over two wavebands ("Long" and "Short"). An internal moving iron cone loudspeaker is present, and the adjusting screw for the pole piece is in the centre of the grille.
This radio dates from 1929 when it cost Ł18 18s.0d.
Note that a replacement grille has been fabricated for the model in the accompanying photograph.
Go to the reference page - a photograph of the instruction card is available on
the "More information" link.