This article examines the “curtain burner” or those 1930s radios that were furnished with a resistance line cord that supplied vacuum tube filament voltage as well as power the radio itself. I’ll look at how possibly restoring these types of radios can be problematic, and how to safely restore them.
Sidereal time is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it’s possible to easily point a telescope to the proper coordinates in the night sky. A fellow reader of N&V contacted me about a digital clock that counted and reported standard and sidereal time, both in 24 hour format. It needed some work, and he sent it to me. Here’s how the restoration went.
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.
This modern take on the tube tester is a must-have for anyone who regularly works with tube-type electronics.
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.
