H. P. Friedrichs (AC7ZL) Homepage
Instruments of Amplification
Here, you can take a look at images associated with the projects appearing in Instruments of Amplification.
This is an example of an electro-mechanical amplifier. I call this one the "Microphonic Relay." This instrument is built from pieces of an old telephone headset, copper pipe fittings, some threaded rod, a bit of steel, and a wooden base.
The Microphonic Relay is so simple to build, it's feasible to build several of them. In use, they can be cascaded, one after the other, to build a chain that produces more amplification than any one instrument could alone.
This is a closer look at the cluster of Microphonic Relays above. I admit it, it's an attempt to produce an "artsy" image.
This represents one of my initial attempts at building an electromechanical amplifier, a design that evolved to become the "Balance Beam" amplifier. To your left, you can see a pair of voice coils (harvested from the ringer mechanism of some old desk phones) and a stack of bias magnets removed from some old cabinet catches. The floor of the tin can serves as a diaphragm. To the right, you make out one of the carbon contacts, which was harvested from a flashlight battery.
Inspired by the Brown Amplifying Relay, this instrument is an extremely sensitive electro-mechanical amplifier, I call the "Balance Beam Amplifier." Carbon and graphite electrodes, brought into contact by a delicate balance and modulated by the vibration of a steel diaphragm, this device is capable of significant power gain.
I experimented with several ways to produce vibration-sensitive capsules. This one uses turned carbon cylinders, one fixed and one moveable, fitted to the interior of a section of a glass blood serum tube. The space between the cylinders is filled with polished carbon granules.
This shows a version of the glass vibration capsule in operation. The left side of the capsule is held rigid. The right side is attached to a metal reed which is mechanically influenced by the magnetic field of voice coil just off to the right.
This represents a collection of vibration-sensitive carbon capsules that I tinkered with.
Transformers may be used to match the drive characteristics of an energy source to the characteristics of a load. This is a clever impedance matching transformer wound on sewing machine bobbins and cored with strands of iron wire
Glow tubes are fun to play with, and have some use in helping to gauge the performance of your vacuum system. This well-worn tube was made from an old spice bottle. Note the reddish-brown deposition toward the left end of the bottle. This is a copper film that was deposited on the glass through the effects of sputtering. It's more or less transparent, yet it conducts electricity! Nifty. Click here to see a brief movie of the glow tube in operation.
This is what I call the "Bell Jar Audion." Modeled after the Audion of old, this tube features planar construction, brass electrodes, and a custom feed-throughs which bring signals into the interior of the bulb.
Here's a neat shot of the Bell Jar Audion in action during initial testing. That brilliant white you see is caused by the filament.
This is a closer view of the audion in operation
This is the second in a series of thermionic triodes, based on votive glass, that's featured in the book. I call this one the "Tennis Ball" triode because of the overall appearance of the glass globe. Notice the coaxial arrangement of internal electrodes.
(revised - 11/03/2005)