This view shows part of
the coil pack and the detector (second stage) tuning condenser.
The two tuning condensers used in the set are identical and have
sizeable brass components and a cleverly designed method of construction.
Unfortunately the set had a nasty fault, typically found in most
early examples of mass produced items before bugs have been ironed
out. When I say "early" I don't mean in terms of the
age of the radio I mean early in terms of its production run.
When I worked in a large engineering business I was "Configuration
Manager" and had to sort out problems such as these. Whenever
a collection of components is assembled the tolerancing aspects
usually make themselves known during the first proper production
run. Holes are in the wrong place, metal bits are too big to
fit in holes and of course there are electronic problems as well.
Everything is made to a tolerance which may be measured in plus
or minus thousandths of an inch, millimetres, picofarads or ohms.
The more precise the tolerance the more expensive a component.
In a cheap mass produced assembly tolerances are therefore quite
broad and when they work against each other the bits don't fit
together properly and the production line grinds to a halt, or
the inspection people get a bit lax - as in the case of this
In this example the tuning dial
which fits on the rear of the tuning condenser locates with a
brass device which is turned by the knob on the end panel. There
is a spring which fits concentrically inside the spindle, on
which the knob is fixed, which tensions the brass fitting so
that it engages with some degree of friction within a slot running
around the periphery of the tuning dial. Normally, rotating the
knob turns the tuning condenser, with a step-down ratio of maybe
20:1, and action is perfectly smooth. However in the case of
one of these tuning condensers, tolerancing was such that the
dial rim, not just the edges of the slot, was permanently in
contact with the brass device. This acted like a brake on the
slow motion operation and imperfections on the rim affected the
friction. Over the years, through repeated use, patches of wear
appeared on the rim and caused the tuning to be not only very
very stiff but very lumpy as well. Over all, operation of the
knob felt very rough and extremely stiff indeed. Strangely the
owner must have never bothered to complain, or if he did was
fobbed off. Perhaps he didn't realise that the nice smooth control
on the right was supposed to be exactly the same as the one on
I removed the tuning condenser
and carefully filed a few thou from the rim of the dial. Operation
of both tuning knobs is now smooth..after a wait of 71 years!