Old Time Radio Engineers

[Nowhere-Man]

As to the book. I did come across a way to measure the inductance of a coil using an electric buzzer and a calibrated crystal radio. I wasn't sure where the book was going with the maths calculation, though. I know how to calculate a resonant frequency using Pi and division by 1000000, plus using square roots but, unfortunately, the book was vague and it helps if they give an illustrated example. Anyway, you use headphones to tune into the buzzing and that should give a calibration mark on the dial you can use perhaps with the fixed capacitor to work out the inductance. Sadly it gives too little detail.

Gosh - that sounds like a complicated way to do it!

Mind you, I can't think of an obvious way to do it with minimal test gear. A signal generator and a volt meter are a sensible minimum, but back then these would have been expensive tools. We're lucky that today, £10 or thereabouts gets one of those magic "test everything" component testers from China.

There is a great way to work out the voltage divider resistances without a current value. I tried it on my trusty calculator. If you have two large resistors and you know the total resistance but not the individual resistances of the divider, it can be done via voltage and proportion. Say the H.T. voltage is 100 D.C. and the anode voltage is 80. The voltage divider must supply the said anode from the source voltage. Simply divide the lesser voltage into the larger voltage. Then divide that acquired sum into the total resistance in Ohms of the divider which will allow two resistance values to be used.

In this book I notice there is a heck of a lot of transformer coupling. It must have been all the rage for a time.