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A Short History of the Galvanometer

A Short History of the Galvanometer


Image of RADIOVISOR LIGHT DEPENDANT RESISTOR, 1940's

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RADIOVISOR LIGHT DEPENDANT RESISTOR, 1940's

Light dependant resistor for use in alarm systems or counting in factories.
Resistance of the unit varies with the light shone upon it, so if the light is interrupted the resistance will change.

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A0563

Image of MERCURY  CONTACT RELAY, 1930's

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MERCURY CONTACT RELAY, 1930's

Switching by contacts immersed in Mercury is almost maintenance free, and can carry reasonable currents.

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A0303

Image of P/X VARIABLE CAPACITOR, 1940's

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P/X VARIABLE CAPACITOR, 1940's

Variable capacitor value changed by sliding inner tube outwards, connections are two push wire clamps. Nothing more is known about this item.

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A1532

Image of LAMP AND SWITCH DEMONSTRATION BOARD, 1910's

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LAMP AND SWITCH DEMONSTRATION BOARD, 1910's

Board with 6 X Lamps one dated 1915, 7 X switches and switch sockets, one dated 1926 and 3 X cards of fuse wire.

This board can be demonstrated.

Bruce Hammond Collection

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A1178

Image of CABLE DUCTS AND FIXINGS, 1930's

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CABLE DUCTS AND FIXINGS, 1930's

Various type of cable management including wooden trays or Ducts with covers and Porcelain blocks for running cables on the surface of walls to light switches etc. Also porcelain mountings for meter boards still seen today.

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A1455

Image of WIRELESS ACCUMULATOR, 1940's

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WIRELESS ACCUMULATOR, 1940's

2 Volt accumulator used in wireless sets for the heaters of the valves. It was normally given to the local garage, hardware merchant, or cycle shop for recharging. They would give you your spare unit while this was being done.

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A1237

Image of A SELECTION OF EARLY BATTERIES, 1940's

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A SELECTION OF EARLY BATTERIES, 1940's

Dry batteries and accumulators (item A1237) were common before mains electricity was widely available, batteries continued for portable sets, as they do today. The picture represents some of the large types that were used with domestic wireless receivers from 1940 to 1960. Bottom row left to right. Ever Ready AD3 90V HT and 1.5V LT, Vidormax L5507 90V HT and 1.5V LT, Drydex Red Triangle H1136 with 23 taps providing LT HT and Grid Bias, Top row left to right. Exide H1146 90 Volts only, Ever Ready 762 45 volts only. Exide DM538 90 Volts only, and Ever Ready B126 90 volts only.
A0175 to A0181

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Image of GALENA - LION MICRO CRYSTAL, 1920's

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GALENA - LION MICRO CRYSTAL, 1920's

Replacement crystal for 'Lion' detector. Crystal is Galena or Sulphide of Lead. Marked on the box Refills for the Liontron Detector price 1/6

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A0141

Image of 'MICROLODE' LOUDSPEAKER UNIT, 1933

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'MICROLODE' LOUDSPEAKER UNIT, 1933

Speaker with multiple tapped Transformer for 11 X different impedance settings, which are set by the switch. Seven for single valve output stages, and four ranges for push-pull class 'B' output stages. Shown at The Radio Show Olympia in August 1933.

Donated by John Lay

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A0916

Image of EDISON AND BELL RADIO PLUG IN TUNING COIL, 1920's

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EDISON AND BELL RADIO PLUG IN TUNING COIL, 1920's

Used in the tuning circuit of early wireless receivers and crystal sets for changing the receivable wavelength.

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A0297

Image of CONDENSER BANK WITH KNIFE TUNING SWITCHES, 1920's

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CONDENSER BANK WITH KNIFE TUNING SWITCHES, 1920's

Tapped capacitor with selection by five knife switches marked .5-1-2-4 and 8 Micro farads.Probably used with early transmitters or receivers during WW1.

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A0273

Image of TELEVISION PROJECTOR OPTICS SYSTEM, 1940's

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TELEVISION PROJECTOR OPTICS SYSTEM, 1940's

Used with Philips projector Television, Schmidt Optics system. At the time only the UK and France had television services. This item could produce a picture 4ft x 3ft (1.22m x 0.91m).

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A0116

Image of LIGHTNING CONDUCTOR, 1950's

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LIGHTNING CONDUCTOR, 1950's

Used near Aerial lines but slightly higher, to attract lightning away from the aerial.
A direct strike would not protect very much as the voltage would be high enough not only damage the aerial but also anything in the proximity of the wiring, however a near strike would send all received voltages to ground.
In the case of Sheet lightning whole areas can be ionised causing the atmosphere to glow blue in colour, such strikes are generally dissipated and without the conductor wired to ground certain damage would occur.
The base is for display only.

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A0719

Image of KNIFE SWITCHES, 1940's

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KNIFE SWITCHES, 1940's

A selection of knife switches for general switching purposes.From the 1940's&50's
Single pole lever switches switches were often used to protect wireless units from lightning damage, and were commonly seen on window ledges during the 1950's and before.
Normally the lever is thrown to connect the aerial, when the operator is finished the lever is changed over to the other side, which is connected to earth. A direct strike would not protect very much as the voltage would be high enough not only damage the aerial but also anything in the proximity of the wiring, however a near strike would send all received voltages to ground.
In the case of Sheet lightning whole areas can be ionised causing the atmosphere to glow blue in colour, such strikes are generally dissipated and without the switch being set to ground certain damage would occur.
On some of the switches there is a spark gap in the On position, so that if the switch is not in the earth position some of the voltage can jump the gap.

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A0760-5

Image of EARLY DELAY LINE STC, 1970

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EARLY DELAY LINE STC, 1970

Delay lines are used in colour Television and Videocorders. This is STC's early version dating from 1970, and two later production models to 1978

Nortell Collection

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A1426

Image of GENELEX EARTHING SWITCH, 1940's

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GENELEX EARTHING SWITCH, 1940's

Double pole lever switch, these switches were often used to protect wireless units from lightning damage. Normally the lever is thrown to connect the aerial, when the operator is finished the lever is changed over to the other side, which is connected to earth. A direct strike would not protect very much as the voltage would be high enough not only damage the aerial but also anything in the proximity of the wiring, however a near strike would send all received voltages to ground. In the case of Sheet lightning whole areas can be ionised causing the atmosphere to glow blue in colour, such strikes are generally dissipated and without the switch being set to ground certain damage would occur.

Bruce Hammond Collection

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A1513

Image of TELSEN 4 PIN & 5 PIN VALVE HOLDERS, 1940's

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TELSEN 4 PIN & 5 PIN VALVE HOLDERS, 1940's

Telsen 4 pin and 5 pin Valve holders in original box.

Bruce Hammond Collection

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A1512

Image of SCREWDRIVER IN THE SHAPE OF A 4 PIN VALVE, 1940's

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SCREWDRIVER IN THE SHAPE OF A 4 PIN VALVE, 1940's

A large pocket screwdriver with detachable bits in the shape of a 4 pin valve, and made of Wood and Brass, with Steel bits.

Bruce Hammond Collection

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A1510

Image of ELECTRON INSULATOR PINS, 1940's

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ELECTRON INSULATOR PINS, 1940's

Box of Insulator pins for mounting a Wireless Aerial to the picture rail inside a room, giving an inside version instead of an Aerial outside the house. Signal strength for good reception would need to be good, as with early Wireless receivers were not as sensitive as todayís models.

Bruce Hammond Collection

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A1508

Image of EVER READY AD35 RADIO BATTERY, 1950's

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EVER READY AD35 RADIO BATTERY, 1950's

Battery used in portable Radio's for powering the valve heaters. As long as portable valve receivers were still in use, Purchasing these batteries was possible.


Bruce Hammond Collection

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A1507

Image of DRYDEX TYPE 1001 GRID BIAS BATTERY, 1940's

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DRYDEX TYPE 1001 GRID BIAS BATTERY, 1940's

Grid Bias battery of 9 volts with taps down to 1.5 Volts, In early directly heated valve receivers there was no automatic bias for the valve grid, a battery was used to bias the valves grid negative for the correct operation of the valve.

Bruce Hammond Collection

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A1506

Image of HARLIE TONE SELECTOR, 1940's

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HARLIE TONE SELECTOR, 1940's

Harlie Tone switch presumably for headphones or an extension loudspeaker at each end is a pair of sockets for plugging in and out; the wiring inside passes straight through with a selection of condensers to alter high frequency response.

Bruce Hammond Collection

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A1503

Image of HERTZITE & URALIUM CRYSTALS, 1920's

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HERTZITE & URALIUM CRYSTALS, 1920's

Crystals were used in assemblies for the detection or demodulation of radio waves, in early crystal sets. See Item A1318 The term Uralium is just as it says on the tin a trade name and the type of composition of the crystal is possibly Iron Pyrite or Galena. The same could be said of Hertzite. See Items A1494. The tin of Uralium also contains a spare wire coil known as a ''Cats Whisker''. Uralium is listed as a supposed new metallic element announced in 1879, its existence has not been confirmed.


Bruce Hammond Collection

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A1499

Image of VARIABLE RESISTANCE & POTENTIOMETER, 1940's

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VARIABLE RESISTANCE & POTENTIOMETER, 1940's

Two adjustable resistances with straight and circular adjustments. The straight version is made by Readirad and the circular is 400 ohms and is made by Igranic. Nothing is known about the maker Readirad.

Bruce Hammond Collection

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A1498

Image of AERIAL COUPLING/TUNING COILS ST400 , 1932

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AERIAL COUPLING/TUNING COILS ST400 , 1932

Aerial Coupling/Tuning coils used in ''Breadboard'' wireless sets during the 1930's. Marked inside ST 400 Aerial, which stands for Scott Taggard and was made for the home build ST400 set of 1932.

Bruce Hammond Collection

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A1497

Image of 'JIFFY' ALL WAVE CAPACITY AERIAL, 1940's

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'JIFFY' ALL WAVE CAPACITY AERIAL, 1940's

On back of the box reads:- Instructions for fixing. Remove Aerial and Earth wire from set. Connect the red core of the twin lead to Aerial socket on set and black core of twin lead to Earth socket of set, (if there is no earth lead disregard this lead). Connect long single lead to Earth. If you have already an Earth fixed you can join this to the existing Earth, otherwise it will be necessary to add an extra length of Earth wire to Earth tube in the ground or to a water pipe. The performance of ''Jiffy'' Aerial (Trade Mark) is dependent on an efficient earth. Main object of this Aerial is it's amazing convenience. Museum comment. Unless you live within sight of the Broadcast Transmitter or extremely close this device would not be of much use, what is inside is a mystery, on test the only reading found was a capacitance of 0.001uF between input and output.

Bruce Hammond Collection

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A1496

Image of VARIABLE CONDENSERS, 1940's

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VARIABLE CONDENSERS, 1940's

3 Variable condensers used in early wireless receivers, two in original boxes, the Graham Parish Litlos type is 0.0003uF. Price on the box 2/-, the Wavemaster is .00016uF.

Bruce Hammond Collection

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A1495

Image of CRYSTAL TO CRYSTAL DETECTOR, 1930's

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CRYSTAL TO CRYSTAL DETECTOR, 1930's

Detecting or Demodulating the wireless waves in the early days always seemed to be an enigma, eventually the thermionic diode proved a commercial solution, but much work was to be done with other devices, such as crystals such as Galena (Lead Sulphide) with a simple wire known as a ''Cats Whisker'' touching the surface, this was the forerunner to the Germanium Diode, which replaced many of these devices. See A1432 and A1435. Many attempts were made to create a junction between two different crystals as in this case, like the catís whisker method the junction is moveable, giving the impression that better reception can be found by touching the right spot. The type of crystal used in this case is unknown, Tellurium and Zincite (Perikon) is one such possibility, but many more were tried. Crystal receivers were to become popular alternatives to expensive valve sets in the 1920's and the ordinary working man would make his own set at home, creating a popular pastime.

Bruce Hammond Collection

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A1494

Image of GRID LEAK CAPACITOR/RESISTORS & LISSEN CHOKE, 1930's

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GRID LEAK CAPACITOR/RESISTORS & LISSEN CHOKE, 1930's

A Grid Leak resistor is normally used between the grid of a thermionic valve and ground, in order for the valve to function correctly, if the grid was connected to a low impedance source such as a tuning or coupling coil then a capacitor is added across this resistor to provide a low impedance path. Far Left. Lisson HF Choke 76mH not marked. Middle back. Lisson 0.0002uF Mica Condenser with resistor clips and box. Middle Front. Lisson dual holder with two resistors, the terminals are marked LT & G (grid) on one side and P (plate) & HT on the other. Right back. Dubilier Mica Condenser Type 620 0.0003uF and resistor on clips. Front right. Telsen Grid Leak resistor holder and box.
Bruce Hammond Collection

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A1493

Image of INTERVALVE TRANSFORMERS, 1930's

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INTERVALVE TRANSFORMERS, 1930's

Transformers designed for coupling valves between the anode of first valve to the grid of the next. These were used in early breadboard type radio's home made or manufactured. The item on the left was made by Radio Instruments of Croydon around the 1930's.

Bruce Hammond Collection

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A1492

Image of 2 LIGHT SWITCHES & 4 AMP PLUG SUPPRESSOR, 1940's

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2 LIGHT SWITCHES & 4 AMP PLUG SUPPRESSOR, 1940's

Back right, Porcelain toggle light switches, notice the wire entry from the side, the house wiring would have been on the surface. Front right, Turn type switch, most common in European countries this has two positions and can be used to switch two independent circuits. The Aerialite suppressor plug adaptor is rated at 4 amps and fits a standard round 3 pin 5 amp plug, this was used to suppress radio frequency interference from appliances such as Vacuum cleaners from wireless reception, with it's original box, made by Aerialite of Stalybridge Cheshire.

Bruce Hammond Collection

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A1491


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