Books You Should Read: Instruments Of Amplification

Psst… Wanna make a canning jar diode? A tennis ball triode? How about a semiconductor transistor? Or do you just enjoy sitting back and following along an interesting narrative of something being made, while picking up a wealth of background, tips and sparking all sorts of ideas? In my case I wanted to make a cuprous oxide semiconductor diode and that lead me to H.P. Friedrichs’ wonderful book Instruments of Amplification. It includes such a huge collection of amplifier knowledge and is a delight to read thanks to a narrative style and frequent hands-on experiments.

Friedrichs first authored another very popular book, The Voice of the Crystal, about making crystal radios, and wanted to write a second one. For those not familiar with crystal radios, they’re fun to make radios that are powered solely by the incoming radio waves; there are no batteries. But that also means the volume is low.

Readers of that book suggested a good follow-up would be one about amplifier circuits, to amplify the crystal radio’s volume. However, there were already an abundance of such books. Friedrichs realized the best follow-up would be one on how to make the amplifying components from scratch, the “instruments of amplification”.  It would be unique and in the made-from-scratch spirit of crystal radios. The book, Instruments of Amplification was born.

The Experiments

Microphonic relays
Microphonic relays, via H.P. Friedrichs Homepage

The book includes just the right amount of a history, giving background on what an amplifier is and how they first came in the electrical world. Telegraph operators wanted to send signals over greater and greater distances and the solution was to use the mix of electronics and mechanics found in the telegraph relay. This is the springboard for his first project and narrative: the microphonic relay.

The microphonic relay example shown on the right places a speaker facing a microphone; the speaker is the input with the microphone amplifying the output. He uses a carbon microphone salvaged from an old telephone headset, housing everything in an enclosure of copper pipe caps, steel bar stock, nuts and bolts mounted on an elegant looking wood base. All the projects are made with simple parts, with care, and they end up looking great.

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Making Point Contact Transistors

[Jeri Ellsworth] is back at it again. We seem to cover her work a lot here. Her latest video above covers how she created a point contact transistor from a 1N34 germanium cat whisker diode. After opening the glass casing on the diode, she uses sharpened phosphor bronze metal from common electrical connectors as the collector and emitter. A 330 microfarad capacitor charged to 20 volts and then discharged though a 680 ohm resistor to the base and collector leads forms the collector region. Her test jig is a simple oscillator circuit such that a properly formed transistor will start the circuit oscillating and make and audible sound. We look forward to more esoteric knowledge of electronic devices being brought to our attention.