News and Notes to look at:
The 1947 Brush Soundmirror Recorder - Restoration -- February, 2008
New Additions to our "Microphone Locker" -- April, 2002
Wire Recorder Restored to Operation -- January, 2002
Vintage microphones of studio quality really delight us when they arrive at the museum. They are rare, since they're not exactly consumer items, and also are prized by private collectors. Then, from the estate of Al Erdman (former engineer at CJOR), we received some great ones. The prize was an RCA 74B ribbon microphone, known as the "Junior". Of course, "Daddy" would be the RCA 44BX, even more of an icon than the Shure 55 "Elvis" microphone. In most pictures from network radio days, the RCA 44 is there. A photo of Bing Crosby is not complete without one.
To my disappointment, the 74B did not work. With nothing to lose, I opened it up to discover the reason -- no ribbon at all, just a small fragment of a ribbon remnant stuck to the windscreen. Not wanting to burden our treasury with a professional ribbon replacement, I tentatively bought a roll of the cheapest (i.e. thinnest) kitchen aluminum foil I could find. My micrometer measurement of twenty strips gave me a thicknes of 10 microns per strip, which is within shouting distance of the 2 to 5 microns I believed were used in practice. I cut a strip, corrugated it, and clamped it in place. It sounded horrible! The ribbon resonance was up in the speech range. I immediately slackened the ribbon, and the sound smoothed out beautifully! As my web research had told me, the ribbon should be as slack as possible without sagging of its own weight. You can hear the result by clicking on the 74B picture (180 kB, WAV file).
Other microphones in this collection were an RCA "Varacoustic" ribbon, a Shure 556, which is the broadcast packaging of the 55, two Electrovoice RE-11 cardioids, and a Western Electric 633 "saltshaker", with a CJOR call-letter flag. The Varacoustic is interesting -- it has an internal shutter coupled to an acoustic labyrinth, allowing the user to adjust it for a bi-directional, cardioid, or omni-directional pattern. This kind of feature was also employed in the RCA 77D microphones.
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Although not strictly a broadcast item, the museum's Webster-Chicago 80-1 wire recorder fills a place in recording history that is part of the legacy of broadcast tape recording.
This model was available commercially in 1947 for $149.50, about the same time as Mullin was running his demonstrations of the captured German Magnetophons with tape having formulations that were not yet perfected.
Although the claimed frequency response is 70 to 5000 Hz, our example does not seem to achieve that at 55 years of age. Human beings suffer response roll-off with age too! In spite of this, the performance surprises most museum visitors who hear our demonstration. The wire passing through the head-slot produces a quiet twanging background sound. It runs at 24 inches per second, so flutter isn't too bad. If the wire breaks, just tie a knot in it, and away you go -- the inch you lose is only 42 milliseconds at that speed! The wire is only 0.004 inches in diameter. It's fascinating to watch the head as the wire moves -- it oscillates up and down so that the wire wraps evenly on the spools. The action is much like that of a casting reel for fishing. The spools come in lengths that run for up to one hour.
Some technical details: This machine uses four tubes, including the rectifier. A 6V6 beam-power tube functions as the audio output stage for 'play' and as the 40 kHz erase and bias oscillator in 'record' mode. Most of my repair time amounted to doing a thorough lubrication. Anyone finding an old wire recorder like this is advised not to even think about playing a wire until the oscillating head is working flawlessly. If the wire tangles, it goes into the garbage can! Capacitor and resistor replacements and righting some wrongs in some earlier repair work got the recording function working reasonably again. Ask to hear it at the museum.
We also have a radio/phono console combination with a wire recorder built in. The wire take-up spool has been made just the right diameter so that it turns at 78 rpm to play records which are placed on top of it! See it at the museum. We received this unit complete with several spools of someone's Christmas-time recordings from 1952! Go back to the topTo contact me concerning the SPARC broadcast section, e-mail me at
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