Instruments of Amplification

by Pete Friedrichs

If you have Pete's Voice of the Crystal, then you must have this! There is only so much you can do with a crystal set, and then you must move on. And this is where you move on to.

The problem with crystal sets is that all the power that gets into the headphones comes off the antenna. There are no batteries or power supplies. But the antenna can extract only so much power, and there is very little you can do to make the sound in the headphones any louder or any clearer. UNLESS! You add amplification, usually with a transistor or vacuum tube. Once you do that, you open up a whole new world of experimentation, and you'll never want to go back to crystal sets.

Here Pete will show you how he made a microphonic relay amplifier which is really an earphone feeding a carbon microphone to achieve an increase in signal level. On the surface the device sounds ridiculous, until you realize that before vacuum tubes this is exactly how telephone companies amplified signals so they could be carried long distances. It really does work.

Then he'll show you how he built a balance-beam amplifier which is sort of a more advanced model of the microphonic relay. It's an ingenious device occasionally mentioned in ancient radio texts. And you can build one that actually amplifies audio signals.

To get the most out of these devices you need a matching transformer. It's very much like the transmission in your automobile changing the form of the electrical energy so that both the crystal set and the amplifier that follows can do their best work.

Then it's on to vacuum tubes. That right. Homemade tubes. You'll get details on Pete's experiments with spice jar glow tubes, a canning jar diode, a bell jar vacuum triode, a tennis ball triode made from a glass votive jar, a hamster bottle triode, and more. According to the data presented in his book, I calculate that Pete's tennis ball triode has a transconductance of about 400, quite low compared to modern tubes, a plate resistance of about 18000 ohms, which gives a theoretical voltage gain of about 7. And that's not bad when you consider the first commercial tubes on the market had voltage gains in the realm of 8 to 10.

Oh so you want to build a transistor? Pete will show you his experiments with a copper oxide device which didn't work so well. But the point contact device he built using a chunk of germanium stripped from a surplus WWII diode worked surprisingly well. And you can do the same.

You get basic theory of triodes, semiconductors, details on Pete's surplus vacuum pump, details on solid state experiments by others, and so much more. This is one of the most unique electronics experimentation books to come along in decades. Not only can you duplicate Pete's experiments, but you can use this as a jumping off point into bigger and better projects.

Most people buy a radio and plug it into the wall. A few of us are energetic enough and curious enough to build radios from components. And then there's the occasional mad scientist who actually builds his own components. And that's special.

If you're at all interested in electronics, then I think you must have a copy. This is tinkering, experimentation, and inventing at its best. You get a big book, well written, and well illustrated. We've got a copy sitting here waiting for you. Just tell us when to send it! 5-1/2 x 8-1/2 softcover 297 pages

No. 3112 ... $19.95