The set originally had three valves
and is contructed from a miscellany of parts. Note the two transformers.
The brown bakelite-cased one was made by Telsen around 1930,
but the other on the right from much earlier, around 1923, I
should say. The tuning condenser is quite an early type and has
a very pronounced shape to ensure fairly linear tuning over the
medium waveband. Resistors and fixed condensers were also pretty
old when the set was constructed.
The three valeholders are all B4 but
of different makes.. a plain example to the left was made by
Lotus, a Liverpool radio manufacturer, the centre one was made
by Benjamin and is an anti-microphonic type, as is the third
which was made by Bullphone, a maker I've not come across before.
There are three mica condensers, a Dubilier Type 610 on the left
having a built-in parallel 2 Mohm resistor using a Dumetrohm
holder, and two 0.003uF Telsen types.
Unfortunately, several parts are missing,
in particular the tuning coils and of course the valves which
would have been ordinary 2 volt triodes.
Most relatively insensitive
sets of this vintage required what was called "reaction"
which is another way of saying adding "positive feedback".
Increasing the amount of reaction increased the set's overall
gain, until at some point the whole thing would break into oscillation
and howl. Because nearly everyone used a long wire aerial up
to the legal limit of 100 feet which served equally well as a
transmitting aerial, when a set broke into oscillation it would
cause all other sets in the neighbourhood to howl in sympathy.
The tone of the howl reflecting the difference in frequency between
the broadcasting station and the offending sets tuning. In other
words, if the nuisance user was tuned to 351KHz and the broadcast
station was transmitting on 350KHz listeners to that broadcast
station over a range of perhaps 100 yards from the offender would
hear a whistle of 1000Hz. The nearer to the offender you where
the louder would be the howl. Probably the first instance of
I lived in a straight road where
houses all had back gardens of about 70 feet in length. There
were about 80 houses on each side of the road and if you looked
in either direction you could see every garden had a similar
pole at its end and a horizontal aerial wire from this to the
house. Mutual coupling between the aerials would be perfect for
driving all the listeners to distraction. Bear in mind that this
was before television and everyone would be using their radios
and very likely mostly listening to the same "Home Service".
This set uses a crude method
of reaction control and probably caused its near neighbours much
aggravation. It has a 7-way switch (with the white dial) plus
a small compression type variable resistor integrated into the
ebonite case. Presumably you set the coarse resistance using
the switch, then used the variable resistor to fine tune the
amount of feedback. The control has no maker's name visible.
The set's design is pretty typical
for the era. Early sets looked like they would be better placed
in a school physics lab rather than in a living room, but as
the years went by the cabinets became more and more stylish.
In fact one can date most sets from the 30s and 40s to within
a couple of years because fashion dictated their design.
Homebrew sets like this one
tended to reflect the lowest possible construction cost as marketing
of kits and parts was extremely competitive and the weekly magazine
titles in which they were advertised could be counted in dozens.
The purchase of a radio was
a major expenditure for a family and would reflect around two
weeks wages, so on the basis of saving 5% of ones income it would
take 40 weeks to gather the required funds for a purchase. Because
of this, many people would build their own set from parts. This
had a couple of huge advantages. The first was one could circumvent
price fixing by manufacturers that was prevalent at the time
and buy foreign made components which were much cheaper. Secondly
one could avoid paying Mr Marconi who was essentially taxing
buyers for using the patents he'd acquired. This "tax"
payment was included in the purchase price of all manufactured
radio sets which had to carry a label proving the payment had
The set was given to me by my
pal Bob Norman.