The "Acme Four"


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.


Internal view


 Click here for circuit
 Click here to return to Homepage  

 Click here to continue