total-recoil
Well-Known Member
I've been struggling to find more technical resources on valves and their use in radio applications. Part of the reason is transistors gradually replaced valves in the late fifties and many of the original engineers or even labs have died out. Despite that, there is now a consensus that valves were probably superior to transistors as diodes, detectors and amplifiers. So, my special interest (narrow as it may be) isn't yet a dinosaur.
Anyway, there are one or two good books on valves that have been put together in this country (the U.K) but they are mega expensive. Last night I had a clever idea and decided to seach online for American sourced books on valve engineering. The secret is to substitute "tube" for "valve" and then you can find American engineering books. Many of these were based on the Zenith radio that are really class receivers and also damned expensive to get hold of. However, I have found at least one really interesting book on tube radio engineering and figure I'll order it from the U.S. as it's affordable.
O.K., here is why valves are so intriguing and I hope I'm not going to bore people too much (there may be no interest):
They are called thermionic valves. The simplest has a plate called the anode and a heater called the cathode. Both of these are electrodes. When the cathode is heated to red hot temp, electrons form a cloud around the electrode and the mass of elecrons are, of course, at a large negative potential. When we connect a 90 volt battery so that the positive is connected to the anode and the negative terminal to the cathode, current flows. That is, electrons flow to the anode like vehicles going along a main road. However, if you reverse the connections of the battery (i.e.negative battery lead to anode), current doesn't flow because the free electrons are only drawn towards positive polarity.
In radio engineering it gets far more complicated than this but that is a very basic explanation. Tubes or valves developed into triodes, pentodes, heptodes, hexodes, double diodes and so on. You can use them to demodulate carrier waves, mix frequencies to make an IF signal in superhets and, of special interest to myself, to convert alternating current to D.C.
Any of you who may be still reading this, can consider the P.C. or laptop you are now using functions on D.C. but is plugged into an A.C. socket at home. Inside your P.C. will be a transformer and rectifier which basically steps down the 230 or 120 supply to 12 volts D.C. Well, valves can do this as well, the only difference being was you had to use far higher D.C. values so some old radios actually had up to 400 volts D.C, floating about the circuit. The higher values had to be a factor as to heat a valve cathode to be red hot, you needed at the very least a combined 100 volts or more - not a factor with silicone transistors. That's how come silicone left valves behind - you can make them very very small and run them on small voltages.
Also, valves rectified A.C. in a different way to what you'd find in an alternator for example or even a laptop and they had to be heated up first before a 50 hertz A.C. supply could be passed through them.
Anyway, there are one or two good books on valves that have been put together in this country (the U.K) but they are mega expensive. Last night I had a clever idea and decided to seach online for American sourced books on valve engineering. The secret is to substitute "tube" for "valve" and then you can find American engineering books. Many of these were based on the Zenith radio that are really class receivers and also damned expensive to get hold of. However, I have found at least one really interesting book on tube radio engineering and figure I'll order it from the U.S. as it's affordable.
O.K., here is why valves are so intriguing and I hope I'm not going to bore people too much (there may be no interest):
They are called thermionic valves. The simplest has a plate called the anode and a heater called the cathode. Both of these are electrodes. When the cathode is heated to red hot temp, electrons form a cloud around the electrode and the mass of elecrons are, of course, at a large negative potential. When we connect a 90 volt battery so that the positive is connected to the anode and the negative terminal to the cathode, current flows. That is, electrons flow to the anode like vehicles going along a main road. However, if you reverse the connections of the battery (i.e.negative battery lead to anode), current doesn't flow because the free electrons are only drawn towards positive polarity.
In radio engineering it gets far more complicated than this but that is a very basic explanation. Tubes or valves developed into triodes, pentodes, heptodes, hexodes, double diodes and so on. You can use them to demodulate carrier waves, mix frequencies to make an IF signal in superhets and, of special interest to myself, to convert alternating current to D.C.
Any of you who may be still reading this, can consider the P.C. or laptop you are now using functions on D.C. but is plugged into an A.C. socket at home. Inside your P.C. will be a transformer and rectifier which basically steps down the 230 or 120 supply to 12 volts D.C. Well, valves can do this as well, the only difference being was you had to use far higher D.C. values so some old radios actually had up to 400 volts D.C, floating about the circuit. The higher values had to be a factor as to heat a valve cathode to be red hot, you needed at the very least a combined 100 volts or more - not a factor with silicone transistors. That's how come silicone left valves behind - you can make them very very small and run them on small voltages.
Also, valves rectified A.C. in a different way to what you'd find in an alternator for example or even a laptop and they had to be heated up first before a 50 hertz A.C. supply could be passed through them.
