A selection of mid-1920s to the early 1930s components

Click on any item to read about it

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Condenser

 

This is a Dubilier "non-inductive condenser" Type 9200, 0.05uF @ 300 vdc working. The end section is used for securing it to a wooden baseboard. The end is removed and fastened to the baseboard then the condenser is screwed vertically in place and the terminals connected to the circuit.

Radio frequency choke

 

A Lissen HF choke for baseboard mounting. The Lissen Company of London was one of the first in the field and as early as 1923 were advertising a "mystery" device for interconnecting RF valve amplifiers. This device, which encapsulated a switch that was able to be set to the best tapping point on a coil, and an isolating condenser did away with the tuning condenser in the anode circuit of the first RF amplifier. The coil was essentially an RF choke coarsely tuned to the waveband in use. It may have got rid of a tuning condenser but on the downside it reduced the selectivity of the receiver. Selectivity was a problem with early sets as, if one lived near to two stations, both could be heard at the same time unless, either a smaller aerial was used, reducing signal strength, or more reaction was employed, reducing fidelity and giving rise to howling in neighbouring receivers. Lissen also made interstage transformers and special switching distribution boards for series-connecting many sets of headphones (still also called telephones or double-head receivers in 1923) to a receiver.

Coil holder

 

No maker's name just "PAT.APP.FOR" This would have been used to adjust the coupling between to plug-in coils, typically for setting the amount of reaction or feedback between anode and grid circuits in a TRF receiver. This device was usually referred to as a "precision vernier adjustable coil".


Solid dielectric tuning condenser

 

A Telsen variable condenser, having a maximum capacity of 0.0001uF or 100pF in modern parlance.

Solid dielectric tuning condenser

 

A second Telsen variable condenser, having a maximum capacity of 0.0005uF.

Solid dielectric tuning condenser

 

A third Telsen component but having the inscription "REACTION CONDENSER". This has a maximum capacity of 0.0003uF.

Tuning condenser

 

Ormond Engineering Co Ltd were based in London and made complete radio sets as well as many varieties of components including loudspeakers.

This aluminium "Ormond" tuning condenser, Registered number 719828 and Patent number 262215 (this was applied for in October 1925). In the early days many radio components had to have a registration number to indicate that they were approved for use in receiving equipment used in the UK. This measure, which only lasted a short time at the start of formal broadcasting was withdrawn. Each radio set had to be approved for use by the Postmaster General and carried a label to this effect. Modifications had to be duly authorised as well but this was dropped as the amount of administration was probably getting unmanageable. The reason for the measures was probably the result of large numbers of complaints by listeners of heterodynes from oscillating valves employing too much feedback to increase their gain. Eventually, more through educating the listener, was this problem solved and manufacturers' allowed to produce sets capable of maximum gain through setting reaction levels up to and beyond oscillation.


Tuning condenser

 

Made by The Radio Communication Co Ltd of London, this brass tuning condenser has the maker's trade name "POLAR", and the impression 0.0006 on the inside of the end plates. This component like the other shown has specially shaped plates so that the high frequency end of the waveband tuned more slowly than it would have done if the plates had been symmetrical about the spindle. This is known a a "Log" type. "Polar" also appeared on vernier coil holders, for adjusting the mutual inductance between adjacent coils, and filament fuses aimed at preventing the loss of your battery valves when the HT battery was inadvertently connected wrongly. These were advertised by the slogan "7d will save you 17/6d" in 1923. There were also complete Polar receivers. Polar advertised the R.C.C. unit, merely a combined anode resistor and coupling condenser, and took great pains to proclaim its superiority over the coupling transformer when applied in sets having more than one stage of amplification. Of course they didn't explain that you needed more than one stage when you used the RCC unit as the step- up advantage of the transformer was absent.

Because anything associated with radio, in the 1920s was horrendously expensive it was common practice, to not only build your own radio but also your own tuning condenser. For this you could purchase ebonite end plates for a shilling a pair, and aluminium or brass vanes, the former type for as little as 6d per dozen in 1923. Then, the same supplier advertised a complete 500pF tuning condenser for the princely sum of 4/6d plus an extortionate 1/3d postage. Things never change!

Low frequency coupling transformer

 

Made by Varley, this transformer is marked, "Niclet For Radio" . It is marked as having a ratio of 5:1, but strictly speaking means 1:5 as it is a step-up device giving a significant signal gain between, for example a detector stage and a low frequency amplifier. Inside the transformer will be an enormous length of extremely thin wire. The secondary winding having five times as many turns as the primary. This is later model as it is fully encapsulated and uses bakelite.

Wavechange switch

 

A Dubilier "MINICAP" marked RD597647. This could be used in any application but would be best for wavechange switching because it is designed to have a low capacity, hence a small effect on the tuned circuits to which it is connected. Switches of this date would have selected Short or Long waves. Short would have referred to the medium waveband as at this date proper short waves were generally thought to be of no use.

Trimmer condenser

 

This is an uncommon component that allows a circuit to be adjusted in track with another. Using this technique allows two tuning condensers to be ganged together instead of being separately adjusted to a particular station. It has the brand name "FORMO" and the name "DENSOR" has been coined for it. This one has minimum and maximum capacities of 0.000025 and 0.0003uF (25-300pF) respectively. Another use might have been for presetting the connection to a long-wire aerial. In this application, trading off input signal for improved selectivity, or the ability to separate out adjacent stations without mutual interference.

Grid leak

 

A Lissen component having the Patent number 252759. This is a very high value resistor used for applying grid bias to the grid of a valve whilst maintaing a very high input impedance to the small signal applied to the grid from the preceding stage. If too low a value is used this would un-necessarily reduce the level of the input signal.

Insulators

 

This little box labelled "ELECTRON INSULATOR PINS" contains just one remaining pin. It was made by the New London Electron Works Ltd., East Ham. It was important to preserve as much of the incoming aerial signal as possible. The tiny hard-earned radio signals, perhaps emanating from thousands of miles away would do their work much better at the crystal detector rather than the damp plaster of a house wall. Whether or not the public knew about insulation I don't know.. but if a lead-in aerial wire was rubber or plastic covered maybe these insulating pins where not required? If the wire was bare copper and the walls were damp then they would be a useful thing to have. These things cost the then princely sum of 6d and were sold for tapping into a picture rail so that the aerial lead-in could be taken to the back of the radio without touching the wall.

Dial cord

 

Worth more intact as a curio than merely using to repair a broken cord! This small wooden drum, contained in a tiny cotton draw-string bag, carries a green-coloured cord and is labelled "The Titan Line". Alex Martin of Glasgow, Edinburgh etc clearly thought a selling point was his "25 years reputation" and his "10 years guarantee". Who were they and what happened to the Titan Line factory? Presumably his cord must have pre-dated its use in dial mechanisms?

Early Dials

   

The earliest radio dials were calibrated 0-180 degrees and a log had to be kept referencing stations to dial readings in degrees. Later, when stations were allocated firm positions in the radio spectrum, set manufacturers' were able to mark these on the radio dial. At this stage dials were calibrated in meters. The example on the left has a centre calibration giving degees from 0 to 180 and also a "LW" scale from 1000 to 1900 metres and a "SW" scale from 225 to 575 metres. This pre-dates the term "Medium Wave" and the days before even the top end of medium waves had been proved to be good enough for reliable for broadcasting.

Because the dial is marked in wavelengths it must have been made for a specific coil/tuning condenser combination and has probably been salvaged from a commercial set. Can anyone identify it? It's engraved, "1008 MONIX SCALE Prov pat number 16523/31". Presumably 1931 from the patent number?

The dial on the right, interestingly is marked in the opposite direction to the first with the longest wavelength fully clockwise instead of the more common highest frequency fully clockwise. This one has dispensed with the logging scale but still precedes station markings so possibly 1932-34? Anyone recognise the radio from which it was salvaged? 

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