Civilian Wartime Radio - Further Notes

[Terry]

 Various component values were subsituted because I hadn't got any of the original values.

Not surprising in many cases as the original values are no longer available! At the time these sets were made, the tolerances of capacitors were such that, except in unusual circumstances, the values of the waxed paper capacitors followed a 1, 2, 5, 10 etc, series. (From memory, I think some manufacturers used 2.5 rather than 2, but it makes no difference.)

In the 60s, the polyester types that replaced them could be manufactured to much higher tolerances and started to be introduced with values in the E6 series, thus 1.0, 1.5, 2.2, 3.3, 4.7, 6.8, 10.0 - there being 6 values per decade following a logarithmic series.

Thus you had to replace all of the values ending in 5 with values ending 47. If there had been any 0.2µ, 0.02µ or 0.02µ capacitors you would have had to use 0.22µ, 0.022µ and 0.0022µ (or 2.2nF) values. In fact you did have to use a 22µ electrolytic for the same reason. Unless anybody redraws an old circuit from scratch, I doubt if anybody would bother to update it.

If you want to understand why resistor values, in particular, have such an apparently strange sequence of values, this chart will be of use to you:



Click on the image for a larger view.

You will immediately see that all the values neatly butt up against their neighbours (or very, very slightly overlap) at the extremes of their tolerance range