Homebrew TRF Receiver from the early 1930s

 This old radio set is typical of a working man's receiver from the early 1930s. Remember that there was a depression around that time. Most families had very little money and the price of a ready made receiver was several times the average weekly wage.

There were dozens of magazines aimed at informing the public how the man of the house could make his own receiver and, no doubt, this particular set had its origins in a publication such as "Practical Wireless".
 
 I should say that this set uses a ready-made cabinet as the top bearer for the nicely figured ebonite front panel is dovetailed into the sides, and you'd think anyone making a case from scratch would probably not bother with this detail. I suspect the set had a single RF stage with reaction plus two audio stages and could probably drive a loudspeaker if a strong station was tuned in.
 

 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 anti-social behaviour.

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 been made.

The set was given to me by my pal Bob Norman.

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