crystal4.mpg скачать в хорошем качестве

crystal4.mpg

The addition of a triode valve (vacuum tube) to our simple radio makes it work much better. As a crystal set, we had got good selectivity on the medium wave; but the price of this was a very low signal level - so low in fact, that the 3 stations we could receive were very faint in our headhpones. Adding a valve did the trick! We used a Cossor 210-DET valve, a type which was around from about 1930. It could both 'detect' our incoming AM (Amplitude Modulated) radio signal, and also amplify it. We attempt to explain how these things occur. We hope we have got the explanations right! We also mention how expensive valves were to buy in the 1920s & early 30s. Valves were 'high tech.' in those days; and besides, you had to get a 2 Volt lead-acid accumulator to feed the filament of the valve, and a high-tension battery to feed the anode - they weren't cheap either.