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 originally from WE0H but now by way of the web archive's "Way-Back Machine"(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.

Here's a note from Dave KG4GTI who used the "home broadcaster" circuit in the transformer powered Knight 6-in-1 Lab kit . If you have the 6 in 1 booklet or the circuit diagrams, please send me a copy. I have the schematics for the three-tube 10-in-1 but not the 6-in-1 which uses just one tube, a 6SN7.

Here are some fond memories connected with a similar unit from Allied radio. I thought that you might be interested in the story that goes along with this electronics kit that was given to me as a Christmas present in 1958. In 1958 to 1960 I lived in Key West, Florida and built an "illegal" broadcast station in my bedroom using a 6 in one kit that went together with fahnestock clips and wire, a breadboard project. The center of all of this was a 6SN7 dual triode. Power supply was a selenium rectifier. By trial and error I worked out an antenna system that put out a great signal that covered the whole island of Key West. Three miles one way and two miles the other, and no harmonics. I played popular music of the day after school, and classical music in the late evening. I even had listeners. I would put on a long playing record and take my bicycle around town to check the signal with a transistor radio and to listen up and see if anyone was listening. (Not many air conditioners in those days, so doors and windows were open). I would record commercials off of a local radio station using an Ampro tape recorder and play them on my station. I would sign off every night at midnight with a really great version of "Beyond the sea" on a 78 rpm record.

Much later there was a local ham who got nervous about my radio station as I also had a friend down the street who also got on the air. This ham told us he was going to turn us in to the FCC, so I got worried and stopped. Later we found out why the ham was so concerned about us. He was obviously afraid our activities would attract the FCC trucks and monitors, because about two months later he was arrested for using his ham radio to sell guns to Cuba for Fidel Castro. Later I went to Miami to take the FCC exam for a second class license and saw all of his confiscated radio gear in the evidence room with his name on the tags.

I had two friends who got interested in radio because of this and both went into broadcasting, albeit behind a microphone. I later went into broadcasting for a short period, but the business was changing by the mid sixties and I didn't like where it was going, and the on air pay was not that great either, so I went into the technical end of things with a 35 year career at the J.F. Kennedy Space Center here in Florida in ground communications.

That little 6 in one kit definitely determined my future, and I wouldn't change it for anything. I have also accumulated a lot of boat anchors and a ham license, KG4GTI. I am now 71 years old and retired from K.S.C. since 2003. Since my retirement I have also worked as a broadcast engineer at a local radio station... I still have a one hour radio show on this station every Sunday at noon. I play 50's and early 60's rock n' roll music. All coming from my home studio using a restored "Gates Yard" and RCA 74B microphone, and real vinyl, turntables, and cart machines, just as it was back then. It's "Dave's Time capsule" on WPGS A.M. 840 Mims-Titusville, Florida. Our signal with only 1000 watts A.M. covers from Melbourne, Florida to Daytona beach and from Titusville, Florida to beyond Orlando, Florida. We are also on the internet world wide at local 840.com.

Dave Watkins. (AKA Dr. Dave at the station).

Thank you Dave and best wishes with continuing the music.

The following is from John WA0FDV

Just came across your review of the famous Knightkit Broadcaster.

I built this little kit in 1960 or 61 a few years prior to getting my ham ticket. I used it as a guitar amplifier as well as a broadcaster. I then talked a couple of my friends in the neighborhood into getting one and we had a nice little 3 way get together on the air, calling ourselves the 'midnight modulators', after the book by Walker A. Tompkins: SOS at Midnight. Yes, we used longer antennas than, um, "recommended."

Probably the most interesting part of my little story here regards the day I decided to take it mobile. One of the friend's Dad did some traveling for his work and he had an adapter for his electric shaver. So we "borrowed" it and I pulled the antenna out of the radio on the old 49 Chevy and connected the Broadcaster to it, plugged the adapter into the cigar lighter and the Broadcaster into the adapter. Away I went with the guys listening to see how far I could go and still be heard. As I remember I was able to go about a mile before they lost me.

Can you imagine how that little adapter was huffing and puffing working to power those tubes. I can't remember anymore if it was ruined in our experiment.

I had previously built the Knightkit Span Master regenerative receiver, and in July of 1957 I built a little RCA "Prep Kit" one tube AM broadcast receiver. A 1T4 vacuum tube. It used binding posts strategically placed on a hard paper schematic on a perforated masonite plate. The hard paper had a schematic on each side. One side was a Diode Detector and the other a Grid Leak Detector. On the four corners of the masonite board you fastened wooden dowel legs long enough to accommodate a 45 volt battery for the B+. A 'D' cell provided the filament voltage for the 1T4. Then you slid the whole thing into a cardboard cabinet. Head phones only of course. I wonder if anyone remembers this little receiver kit. Maybe it would go for $300 on ebay today...HI. I still have it, as well as the Broadcaster. 73, John/WA0FDV

Thank you John. That cardboard RCA is an interesting piece as well.

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, 6-15, 1-20