COLOUR CODE.

Resistors and capacitors.
Also sometimes used for other components.

3 bands = 1^st digit, 2^nd digit, 3^rd band = multiplier, then space.

(Body-tip-spot, is order for old resistors.)

4^th band = Silver 10% tolerance;
Gold 5% tolerance;
Pink band = high-stability.

OHMS LAW.

  E
I x R

E = Voltage; I = Current; R = Resistance, W = Power. (in Volts, Amps, Ohms, Watts respectively.)
Also: E x I = W; I² x R = W; E²/R = W.

The "E" used to be "V" for voltage, until some bright spark (?) decided that "E" for electromotive force would be more likely to confuse the uninitiated.!

Copper wire can be used as a substitute for fuse wire.
The table shows the size and the current at which it will fuse..

S.W.G.                  Current (Amps)
46                             1.25
44                             1.85
42                             2.6
40                             3.4
38                             4.75
36                             6.8
32                            11.5
30                           14.15
28                           18.45
26                           24.75
24                           33.33
22                           48.00
20                           70.00
18                         105.00

Almost all valves required a high tension supply. Some valves were designed for the voltages readily available by rectification (to DC) from the (AC) mains supply. These were both 90 volt (for a 110v supply), and 200 volt to suit a 220v or 240 v supply.

When equipment was required to operate away from the mains, there were several options.

1. Batteries. Several types of 90 volt batteries were made, but these only had a limited operating time.
2. Petrol engined (or steam engined) generators were used in some cases, especially during WW2.

Where the equipment was to operate in a vehicle, the existing 12 volt (or 24 volt) battery supply could be used to provide the high voltage required.
There were two main methods of generating the required voltage.

Motor-generators.
A battery powered motor coupled to a dynamo that produces the required voltage. Although some early versions had separate motor and generator, in most cases, they were combined, and sometimes had multiple windings to produce several different voltages. They were rapidly superseded by VIBRATORS for domestic equipment (such as car radios) but remained in use for military and some commercial purposes for much longer.

Vibrators.
The vibrator is basically an electric switch that interrupts and reconnects the incoming supply from the battery, several times per second. (Take one apart and the mechanism is similar to that in a door bell or buzzer.)
This interrupted-supply, which is AC, feeds to the primary of a transformer, the secondary winding of which, having many more turns, produces a high voltage. The interrupted DC at the input is still present at the transformer output and has to be converted to DC for use in the equipment. This was usually done by passing it through a rectifier, which converts AC to DC.
Another method was to use a synchronous vibrator which had a second set of contacts through which the secondary was passed and which, after smoothing, gave a DC output.

Vibrators were notorious for producing an irritating buzzing noise while they were running. It was often caused by vibration of the outer aluminium can which covered and protected "the works". One cure was to wind several elastic bands round the can.