With a fair number of 1920/1930 radio components still lying
in a box, it seemed worth trying to breathe some life back into
these 70 year old components.
A check revealed enough to create another "vintage style"
radio around a pair of Medium and Long wave "Telsen"
screened coils , together with a slow motion tuning mechanism
with built in Reaction control. Also available was a Screened
Grid valve, together with HF. LF. and Output triodes.
The tuning mechanism was available from a 1920`s commercial
set.
This must have been the original "printed circuit"
layout, the main difference from the modern version (apart from
size) being that the circuit was composed of strips of brass secured
to an insulating board by brass eyelets through which components
were bolted, these being tailor made to fit . It was a very basic
circuit and as both intervalve transformers were defective it
was cannibalised . How simple all these circuits seem today.
The result was `The Acme Four`, similar to the "Compact
Three" but with the addition of an H.F. stage and named after
a design of the 1930`s by the late F.J.Camm.
The variable and increased gain of the S.G. valve allowed
the Reaction control to be far more gentle and the set operates
without the neccessity of bordering on instability.
For any one considering restoring or creating old sets, it is
worth remembering that
intervalve transformers may have at least one winding open circuit
,whilst paper "condensers"of around 1mfd. capacity are
almost invariably short circuit at H. T. voltages. Potentiometers
of those days are likely to have their bushing and spindle live
to the centre connector, producing interesting results if H.T.
voltages are present.
