I have always considered that any wireless collector will eventually have, with some luck, what he may call, 'My find of a lifetime.' That rare item which few others ever find, it being a reward, as it were, for all the effort that he has put into searching for early wireless.
So it was that in an Antique shop, this time in Norbury, South London, I had mine. The shop was run by an Irishman of imposing build, who travelled back to Ireland, dealing each side of the Irish sea.
There was nothing in his windows on this particular occasion so I wandered in looking around, but didn't spot anything of interest. Just as I was about to depart from the shop the owner came out from the depths of the furniture and asked me what I was looking for. I told him, old radios. He said that he had something that an old sailor had brought in recently, and he dragged out a large, dirty, sack covered cardboard box from the back. Yes, an old sailor he said who had been hard up so wished to sell his old radio.
"It's in 5 pieces," he said as he dragged the box forward and I began immediately to lose interest in a radio that was in five bits! An empty, badly scratched, woodworm embellished cabinet with torn fret. A rusting chassis, a loose grotty loudspeaker with a bashed in cone, frayed line cord and a few sad looking wobbly valves were all pictured by me as being a 5 piece radio!
But to my amazement on examining what was under the sacking, I realised that this was a very early example of a unit constructed wireless. Maybe home made, I thought, as this method of unit construction had been used by wireless experimenters up until about 1924.
But engraved on the panels of each of the five units were the magic words, which made me check that I had a wallet on me, "The Marconi Scientific Instrument Co," at that time a company that was unknown to me.
"How much," I asked, trying to hide my excitement. "Saaay 35 quid. OK?"
Yes that was certainly OK. Into the back of my car went the old cardboard box and its contents.
So this was my, "Find of a lifetime."
This 5 unit 3 valve receiver used as the HF amplifying valve in one of the units, the early V24 Marconi triode, which has the filament connections brought out each end with the grid and anode each side. A very early example of low inter electrode capacitance and low loss construction. This small valve is similar, in that the electrode connections were brought straight out of the glass envelopes, to that which helped win WW2, namely the famous EF50. Timely then that the V24 helped in WW1 and the EF50 in WW2 in radar.
These Marconi Scientific Instruments were made before the BBC was formed so had no Post Office marks on them. Made about the same time as Capt. Eckersley of 2LO fame had invented the quietest volume control ever designed by moving the microphone nearer or further from the performers! It was just a few months after the start of broadcasting from 2LO that an advert for these Marconi unit receivers was placed in Wireless World in July 1922 probably as sales of all wireless equipment would have been given a big boost by this broadcasting event.
These units were sold in any combination as and when money was available. A 6th unit which could also be added containing a low impedance telephone transformer, but this last unit was missing on the example I found. Well, what do you expect for 35 quid?......!
The system consists of one unit as a retroactive unit containing the tuning coil and swinging retroaction assembly with a compartment to hold 6 push in coils for the tuning ranges. These extended the range up to 26,000 metres reflecting the experimental nature of these early pre BBC receivers. Because of the large range covered the retroactive coil is tapped by a stud switch mounted on the moving coil. A range coil, on being pushed into position, engages a button which switches the LT on for the rest of the units. So for retroaction one had to, "swing and switch."
Unfortunately, some of my coils are missing. Maybe the old sailor dropped them overboard one stormy night!
The retroactive unit with 6 coils in 1922 was priced at £13. Retroaction, or Regeneration (later called reaction), was first patented in the UK in June,1913
jointly by C. S. Franklin and Marconi ( Patent No 13636).
But to form even a single valve receiver one would also have needed in addition, the large Marconi variable condenser tuning unit priced at £4 together with a detector valve unit at £6. Thus a complete single valve Marconi receiver of this unit construction would have cost £23 in 1922.
For a longer reception range another £6 was required in order to buy an additional HF amplifying unit using the V24 valve (see internal photo). So the three valve installation as illustrated, which also includes a LF note magnifier stage (see internal photo), which I bought for £35 would have cost a grand total of £34 in 1922. It seems then that I was overcharged by £1 on the original retail price! Shall I take it back?
During the inter war period the farm labourer earned on average just over £1 per week and a middle class white collar worker, about £5 per week.
So the middle class would have had to pay over 6 times their weekly salary to buy this three valve receiver and a farm labourer about 30 times his. At today's minimum wage (relative to the farm worker in 1920s on £1 per week), that is equivalent to approximately £6,000 today and for this one can buy a top of the range PC, a coloured TV, a digital camera, and a GPS and still have change for a pint of beer!
Of course, the PC and TV etc.(and the beer!) are mass produced whereas the Marconi units were not, but it is a great tribute to the advance of technology how the power of money has changed and what it can now purchase in spite of the huge inflationary increases in the intervening 80 odd years.
Other manufacturers of this early period also made these unit type receivers. Pye, Sterling, Tingey, Halycon and others. Home built construction by unit system was popular too as it enabled additions to a wireless without having to alter the existing. Just build or buy and reconnect a few terminals for extra HF or LF stages. The 'Boys Book of Wireless' in 1924 also described a unit receiver for home construction as does, 'Harmsworth Wireless Encyclopedia.'
There are a total of 50 terminals to be connected on this 5 unit Marconi. Quite a good chance then for noises off due to terminals not being screwed down tightly.