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.
Are you an audiophile with a yearning to build kits reminiscent of the old HeathKits? If so, then this high-end tube amp kit may be what you’ve been waiting for. I think you’ll appreciate the value proposition of this eight watts per channel single-ended stereo amp based on a pair of 300B or 2A3 triodes.
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.