In Part 1 of this series, I covered basic sweep alignment theory and construction/operation of an all-in-one sweep alignment instrument I dubbed the WhippleWay Sweep Alignment Board (or WSAB for short). In Part 2, I’ll describe sweep alignment procedures for AM and FM radios and give an actual example of each.
This article — a continuation of the series on the restoration of broadcast receivers — details the restoration of the Zenith G725: an AM/FM receiver introduced in 1950. This radio makes a great first tube project because the plum Bakelite case is easily restored, the radio is affordable ($25 and up on eBay), and documentation is readily available.
The popularity of repairing and restoring tube radios has highlighted the need for a variety of test instruments. After repair or restoration of a radio, the final step is often alignment. For an AM radio, a signal generator and voltmeter will do a good job. But with an FM radio, using a signal generator and voltmeter does not always produce the best results. So, I came up with my own design using a digital signal generator module, Arduino processor, and digital display.
Even though they were invented well over 100 years ago, vacuum tubes are still interesting, rewarding, and worthy of investigation. Plus, building with tubes reviews the history of the technology and promotes an understanding and appreciation of its development.
This modern take on the tube tester is a must-have for anyone who regularly works with tube-type electronics.
In the 1950s and ‘60s, Popular Electronics and other magazines carried ads for strange looking machines called Geniacs and Brainiacs. The ads claimed they were “electric brains” that could play Tic-Tac-Toe and NIM. A while ago, I bought several sets on eBay and I would like to share my experiences of learning about them and my sometimes frustrating — but successful — efforts to get them to work.
The C22 — one of my holy grail audio electronics acquisitions — is known for quality in engineering and construction and audiophile performance. The C22, which originally sold for $330 in 1965, now sells for between $3,000 and $6,000, depending on condition. Even if you don’t own a C22, by following along, you can pick up pointers for your own vintage restoration project — especially when it comes to restoring improperly serviced gear.
After retirement a few years back, I started collecting AA5 radios, restoring and selling them. People would ask whether they picked up FM and, of course, they did not. I started thinking about how to add FM capability without destroying the AA5’s AM operation. Here is my solution.
Nixies were introduced when vacuum tube hardware automatically provided the high voltage they require. These days, circuitry typically runs on five volts or less, so finding the +170V or so for Nixie anodes can be a bit of a challenge. Here are three transformer based ways to obtain that high voltage in line-powered semiconductor-based devices.
Every restoration — even repeat restorations of the same model — reveals something new about tubes and tube circuitry. In this restoration of the Jubilate, the focus is on reclaiming a circuit board covered with dirt, converting a selenium power supply to one based on silicon diodes, and the best ways to rejuvenate the cosmetics of your radio, including how to refinish a wooden cabinet.
