Knight-Kit Wireless Broadcaster
While hardly a boatanchor, this Knight-Kit Wireless Broadcaster was a fun piece for many experimenters. It was sold by Allied Radio as a kit. The working unit allows the user to broadcast a limited-range signal from a microphone or phonograph. It will also work with a line-level input from a CD or cassette player. Great for sending period music to your old (and new) broadcast-band radios. The tuning capacitor allows setting the broadcaster to an unused frequency from 600 to 1600 KHz.
Antenna length is limited by FCC rules to ten feet. Experimenters in the 1950s tended to stretch this limit a bit :-) Check out the stories from those who built these back when. The following site by Jim Addie specializes in the Wireless Broadcaster. His site has some stories by those who built and used these little gems. See also the story below.
There were two versions. This version with its fully-enclosed chassis was the later one. It was reviewed in Popular Electronics magazine in June 1959 pages 101-102. It has an output transformer that can be hooked to a speaker for use as a low-power audio amp. (The article links are to SMECC, the Southwest Museum of Engineering, Communications and Computation.)
The earlier version, which had an open chassis, was reviewed by Popular Electronics in May 1955, pages 31-33 and 111. It uses a choke in place of that output transformer. Both versions use a 50C5 tube as an oscillator with another 50C5 for Heising modulation. A 12AX7 is used as the audio preamp. These are AC-DC circuits. Although this circuit uses "floating ground" (a resistor and/or capacitor between the metal chassis and the power line), an isolation transformer is strongly recommended for safety. At the very least use a GFCI outlet.
Since most of the parts are still available, a home-brew version of this little transmitter, with some circuit modifications, could make a nice little minimalist 160 meter AM QRP rig. Yes, licensed hams can use antennas longer than 10 feet, at the proper frequencies. "Rig here is a phono oscillator circa 1959."
PDF copy of manual for the Knight-Kit Wireless Broadcaster courtesy of WE0H (7.3 Mbyte file)
Memories from users of the Knight Broadcaster
The Knight broadcaster was a favorite for many teen-age electronics enthusiasts. Here is a note
from Terry D. who apparently plate-modulated the broadcaster via an external audio amp (and used a longer antenna!)
"When I was a kid, around 16, I bought an Allied Radio "Broadcaster"'. I was working on a Seeburg juke box and my buddy and I hooked the output of the broadcaster up to the 20 watt amp. We didn't know anything about impedance matching or coupling. The output was fed through an output transformer hooked up backward to my Ham long wire antenna, and a ground. I guess we were lucky we didn't kill ourselves. Anyway, the darned thing worked. I had a Wilcox-Gay Recordio that we used as a mixer. I know we had about a 10 mile radius because we could be heard in two neighboring towns. We finally got shut down when a parent heard us broadcasting private phone calls. The FCC didn't get us, but we were suspended from school for a week. I don't think I'd try that now, but it was a lot of fun at the time.
I remember we had the enclosed model. If our model had the speaker transformer, that would explain how we were able to match the amp input. ... I do seem to remember a wonderful blue glow in the outputs, two 6L6's I think. Those old jukebox amps were built like bricks. Anyway, it worked without frying us. It just shows what a miracle it is that some of us made it through our teens."
And a note from Bill R.
"I ran across your site while writing a chapter in a book about the challenges for families in the digital age. I posted on your site when I found your wonderful color photo of Allied Radio's Knight-Kit Wireless Broadcaster. I purchased one in 1960. I later made a pilgrimage to Chicago from Minneapolis just to visit the Allied Radio showroom. (I think I bought a 20' spool of red bell wire.)
My pre-ham days are what got me into voiceovers full time in Hollywood, CA. Started out in Minneapolis with the 5-watt Knight-Kit. I named my AM "radio station" after my 6th grade history teacher Bob Close. With neighborhood buddies I formed the Brotherhood of Radio Stations. We appropriated AM radios from our parents, shorted out the RF by soldering microphones to the volume control, and we were on the air (if shouting into a P.A. system in our bedrooms was on the air.) But the Knight-Kit made it real. I was able to broadcast up to a radius of three houses. I sent a fellow broadcaster out with a transistor radio to his ear. I told him to keep waving as long as he could hear my signal. He stopped waving when he got past the third house.
All the best, and thanks for the memories.
And thank you, Bill. Our hobby activities have led many of us to rewarding careers.
Did you have some interesting youthful experiences with the Knight or other Broadcaster? Send an e-mail. See the home page for the address.
1-22-02; updates 6-04, 4-08, 12-09, 2-14