Yet another junk box (8)

 I keep an eye open for collections of early radio parts. Sometimes, I'll buy one interesting part and the seller will ask me if I want a whole pile more for the cost of postage.. here's another mixed lot..



 Above are two views of a foreign manufactured fixed condenser. The marking .0002MFD means 200pF in modern parlance.

Below is a type 600 fixed condenser made by Dubilier which must be unique enough to carry two patent numbers.


 Below is an interstage coupling resistor/condenser combination. Some of these were intended to compete with a much more expensive coupling transformer between audio amplifying stages but this one would have disappointed an experimenter because it must have been designed for RF coupling as its condenser is only 100pF. The resistor in the clips is a glass vacuum type carrying the marking "500Kohms".




 Above: Two views of an early electrolytic condenser marked 50MFD and 50 volt max working. The patent number is 11476/28 but it carries no manufacturers name. The case is bulging and as you can see it's no longer a functional component.


Below are more condensers, a high voltage non-inductive type of 1uF made by Millgate, clearly once a British manufacturer.

The other uses mica as the dielectric and has a marking "015 MF" or in modern parlance 15nF. The upper case M is now understood to be short for "meg" or one million and lower case m or "milli" meaning one thousandth. However, in this case the M means "micro" which is usually written as "u" or the Greek symbol for mu meaning one millionth. Even nowadays, nearly a century later, these distinctions are still not not adhered to universally. The other common terms are "pico" and "nano" meaning a million millionth and a thousand millionth respectively. At this point I'll touch on the term "billion". Strictly speaking this is a million million but in the UK the term has been hijacked to mean a thousand million. Our continental neighbours however use the term "milliard". I suspect the looseness of the terms is due to plain ignorance, chiefly of the press and politicians who rarely get things right.






 Above are a couple of cheap variable condensers looking well past their best...




 Top: An Agro 2-pin 5 Amp mains plug & socket no longer desirable because (a) it's not polarised and can be turned round and (b) unplugging could result in a shock if fingers are touching the pins. The same can be said of the Goltone 2 Amp version commonly used in homes for powering table lamps before the 13 Amp style was introduced.



 A collection of potentiometers all from the same junk box, the most recent (below) is a 5Kohm wirewound type made by Colvern and dated 1952.

The oldest are two from the days of breadboarding carrying nuts for wiring. For some odd reason the manufacturer, Elpro decided to add a metal tab carrying the resistance value of 5,000 ohms instead of printing this on the body.

The one opposite and the last in the collection have no makers' name and are probably foreign imports.



 Here are some oddments. Opposite a Cossor transformer, probably used for interstage audio coupling.

Below is a socket for a coil which is slighly odd as it has both pins for inserting into another socket plus screw terminals. Next to this is a very early coil socket fixed to an ebonite panel.





 Above is a Telsen aerial coil marked "Variable Selectivity". This faeture is achieved by coupling two coils, input and output, by a small variable condenser. The output coil would be tuned to the desired (weaker) transmission and aerial loading adjusted by the condenser to prevent cross modulation or breakthrough from a strong local station.

Below are three valve holders. The first is a foreign made B7 type with screws for solderless construction as well as solder tags for the more modern method of construction.

The other two are earlier B5 types made by Telsen and designed for mounting on a wooden board. One has additional solder tags. Both have the (P=provisional) patent number 20286 30, with one having a slash 30. I wonder if the "provisional" was ever dropped?

 Next to this (above) is an aerial terminal. Broadcast receivers were restricted to 100 foot aerials due to the fact that early TRF receivers using "reaction" to improve gain were frequently poorly adjusted and able to re-radiate a carrier which upset neighbouring listeners. Limiting aerial length was a compromise between permitting reception of distant stations and limiting the area of interference from an oscillating RF stage.






 Above are two views of a plug-in coil made by Lewcos and shown dismantled on the left. It's shell is made from Ebonite which was also called Vulcanite by some manufacturers. The material pre-dates plastic and was made by mixing rubber with sulphur and forming a product with a press carrying tools to produce the detail required.

Clearly this coil was made with two different tools and it's interesting to speculate why the maker didn't design the two parts so he could use a single tool because these tools were very expensive to produce. The thing carries a lot of decorative detail which would have added to the tooling costs.

The coil comprises two identical windings each having a DC resistance of about 1.3 ohms. The pair have a common connection terminated at the metal wander plug socket in the coil centre and each has an inductance of 57uH. If the pair are wired in series and used with a standard 500pF variable condenser the combination will resonate across the medium waveband. Used singly the result will cover the band from 1000Kc/s to 2900Kc/s.



Below is a Lewcos advertisement from the 1928 BBC Yearbook. Note the name "Lewcos" derives from "The London Electric Wire Company".




 Finally, an example of a Lewcos coil used in a home-built receiver from the late 1920s.

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