Welcome to the world of home wireless broadcasting!  

Many of us participated in this activity in our youth and... where did it lead?

Below you can view a group of stories and memories of some of those experiences. We welcome the submission of  your story to add to the collection here.

We will also  establish  sections of review articles of home broadcasting units, schematics, etc.

If you have anything that is not listed here please contact us and we would be happy to post it or if a three dimensional object add it to the museum's display.  

Click to  enlarge

See the Popular Electronics articles on both models
of the Knight Kit Wireless Broadcaster Click Here

POPULAR ELECTRONICS
Builds a Wireless Broadcaster-Amplifier

SEMCO ELECTRONICS

DELUXE MODEL T-51

BABY SITTER BROADCASTER

"PAGE BOY"
Models
 T-50  - T-51
Baby Sitter  Broadcaster

Operating Guide and Instructions

RADIO BROADCAST INTERFERENCE:- To select a new frequency, plug radio into an outlet about 20 feet away from Page Boy and dial to a silent spot near 550 kc with radio volume on about half way. Then adjust screw in back of Page Boy by rotating slightly (VERY SLOWLY) to the left (500 to 550) or right (550 to 600) until a howl (acoustic feedback) is heard at the loudest level. Reduce volume on radio and retune to finest point. You now have determined the new listening frequency for use on this radio as well as on others. The Page Boy signal can also be heard with reduced power in the harmonic range which is double and triple the original frequency. For instance, if the pre-set frequency is 550kc, the signal can be heard at 1100 kc and 1650 kc.

Noises from electrical appliances which interfere with ordinary radio reception will also interfere with the Page Boy signals. Our Z2 filter may also be used on the offending appliances and the results in quieter radio reception as well as Page Boy operation are usually worth the investment.

IMPORTANT---DO NOT CONNECT FILTER TO PAGE BOY UNIT.

No wiring needed! No installation!

Simply plug in like a lamp

The "Broadcaster" transmits through your radio without connecting wires exactly as "Baby Sitter" model T-50, excepting that it has more tubes and greater power for long range broadcasting. Has many additional features:

· Built-in power switch for easy operation.

· Ivory Plaskon cabinet which blends in any decor.

· Matching ivory handle for easy carrying.

· New circuit design with four latest developed electronic tubes.

· Clearer reception with speech clarity.

· Extra sensitivity. . . you can actually hear the sound of baby's breathing. Visit your neighbors several houses away and the "Broadcaster" will warn you on their radio anytime baby's fussing.

ATTRACTIVE IVORY PLASKON CABINET

This text from  brochures provided  by Jonathan D. Bromberg - W1JDB
In memory of  his father  William L. Bromberg of Rockville Center N.Y.

We have  other brochures and units of other 
models by this manufacturer as well.

      SEMCO Electronics 'Page Boy Electronic Babysitter Tube type from the 50's In the Museum's collection. Many units were produced  to monitor children remotely. Of course many industrious young folk got hold of them and turned them into neighborhood broadcasting stations also!

Graymark 515 home broadcaster

This link will take you to  schematic and chassis layout diagram.

As a matter of fact at the age of 13 my Dad bought an old 78 rpm phonograph.
It had one tube and to listen to it you had to use the AM radio and turn the
dial way over to the edge.  Well, some neighbors heard it and found out who
it was so they started calling in requests on the telephone.  It was
amazing.  Without an antenna it was broadcasting up to 4 miles away.  Soon
everyone was getting in on it.  This was in 1958 at Ketchikan, Alaska at
mile 11 North Tongass near the Totem Bight park that many of you might have
seen in pictures about Alaska. There was only one radio station on the whole
island back then so no one seemed to mind.  Years later my first job in the
US Army was ...yep...a radio repairman.

I have one of the little Knight-Kit blue TX myself. I built it around 1960.. The thing remembered most is that I got a few nasty shocks when hooking it up to my sisters little portable phono which was also hot chassis.

Hooked it to my 40' long SWL antenna and walked the neighborhood with a Truetone tube portable of 1958 vintage...  Only got a usable signal one short block away... But for a 14 year old it was fun....  It's sad to see how few kids today have the interest to just tinker with stuff. 

KD4HSH

No pictures I am afraid, but mine was a homebrew 807,
grid modulated by a plastic K-Mart record player!!
I used a 1400 kc/s crystal though (sophisticated eh?!!)
Not sure where the rock came from but the
station worked very well from the third story of a
fake "windmill" type building that served as the poolhouse/laundry
of our apartments in Georgia. It started out life in a construction shack, but that was of course lower to the ground, and the
AM signal traveled much farther after going up to that
3rd story level!

Bob Richards Tells Us:

Black Thread and Ford Coils

Pete Petersen WY7Z

            In my old neighborhood over 60 years ago, Gene and Kenny were my close friends and school chums. Gene lived on a corner and I lived two houses away. One day we decided to put up a string an and tin can telephone between our houses. Empty cans and spools of black thread  were quickly provided by mothers happy to supply whatever might keep us out of mischief. The lady in the intervening house gave us permission to put our telephone line across her yard and through her tree after we promised not to fall from the tree and break our necks.

            It took many tries and much broken thread before the telephone was a success. volume was adequate, as I recall, in spite of the thread rubbing against tree limbs.

            We tried without success to string a second line between Gene and Kenny’s house. Their houses were separated by a broad street with a grassy median wide enough for us to play football in. We succeeded in running thread between their houses but the distance was too great and the thread sagged so much in the middle that a passing truck carried it away. Some other communication system was needed.

            I don’t recall whose idea it was, but a wireless system was proposed using Model T Ford spark coils. Ford coils were marvelous things, housed in a nicely joined wood case with a vibrating current interrupter on one end. They produced a high enough secondary voltage to make a blue spark jump across a half inch gap. By asking around the neighborhood we found several men who had owned Model Ts and who gave us left over coils. 6 volt batteries were free also; service stations were glad to give away old batteries that would no longer start a car but had enough power for our purpose.

            The transmitters were simplicity itself: a Ford coil, a homemade spark gap, wires for the aerial and ground, and a telegraph key made from a hacksaw blade.. Of course we knew nothing about amateur radio,  licensing, frequencies, Morse code, or other niceties.

            Being completely untuned, these transmitters probably covered the entire radio frequency spectrum. That was good in a way because we could receive our signals with any broadcast receiver tuned to any frequency. Fortunately there was no television to interfere with and we never heard any complaints about interfering with radio broadcasts. The latter was probably because we lived in a working class neighborhood where radios sere usually operated by the man of the house after dinner when we were doing our homework or were in bed.

            With our family receiver dials set anywhere to hear the buzz of our transmitters we communicated with something similar to Morse code. Kenny was one buzz, Gene was two buzzes, and I was three buzzes. Various combinations of short and long buzzes meant let’s play ball, go to the movies, or whatever.

---

Kit a Knight in Shining Armor

by Jack Cheese

(reprinted from Radio World, April 1, 1987)

Pasadena CA

Back in 1964, when it was still profitable to operate a local AM daytimer, KHGL signed on the air in Pasadena, CA.  The station operated on 860 kHz and covered the city of license well using an end-fed long wire antenna.

But even in the heyday of AM radio, dollars were tight, and the station's construction budget had to be watched carefully.

For this and various technical reasons, the transmitter we chose for the new KHGL was a model manufactured by Knight Electronics.  The Knight transmitter (or Knight-Kit, to be accurate) was ideal for our application.

The transmitter was compact, taking up only l/2 square foot of floor space, and could be powered by 115 volts AC or DC, single phase. There was no need to install three-phase AC service.

It used only three tubes and didn't have any unusual cooling requirements.  In addition, the Knight transmitter included a built-in turntable and microphone preamplifier, modulation level control and an audio output for monitoring program modulation with a conventional loudspeaker.

Even with a relatively low output power of 100 mW, the Knight AM transmitter was rather cost-effective with a price tag of under $12 (plus shipping via UPS).

There was only one catch: As it's name implied, it was a transmitter kit; the buyer had to build it.

The Knight unit was assembled using point-to-point wiring, 1964 was too early for PC board technology.

Do-it-yourself assembly

Assembling the Knight-Kit transmitter was straightforward, thanks to a well written and illustrated manual. The process took about two days.

The transmitter design was conventional, employing three tubes: two type 50C5 beam power pentodes and one 12AX7A dual low-noise triode. One of the 50C5 tubes was the oscillator/RF power amplifier.

The carrier was generated using a free-running oscillator, the frequency of which was determined by a variable capacitor in the “tank” circuit.  The operating frequency was adjustable over a range of 530 to 1610 kHz.

The RF output was taken from the plate circuit of this same tube, and coupled to the antenna with a broadband output circuit. There was no need for plate tuning or loading adjustments; the output section was broad enough to permit adequate efficiency on the entire AM band.

The RF oscillator/PA tube was plate modulated by the other 50C5, the modulator. The modulator circuit was also conventional, except that the modulation transformer primary was wired to the plate of the PA, and its secondary was therefore available for connection to an 8 ohm speaker.  This provided a convenient means of monitoring the modulating signal and eliminated the need for a separate mod monitor.

The most unique aspect of the Knight Kit transmitter was the inclusion of an RlAA-equalized magnetic turntable pre-amplifier.

Never since have I seen any transmitter that actually had an RCA jack on it labeled "mag-phono input.  The 12AX7A tube was the phono preamp, and would provide more than adequate modulation level when used with the recommended GE VRII cartridge.

A ceramic microphone was also provided, and would work when plugged into the "phono" input, though the RIAA EQ created somewhat exaggerated bass response.

When the Knight transmitter was first powered up, there was an unusually bright momentary flash from the filaments of the 12AX7A tube.  We determined this was because the 12AX7A did not have an 11 second controlled warm-up as did the 50C5's, and this was normal.   (The tubes' filaments were powered directly from the 115 volt AC line.)

When all tubes reached their operating condition, full RF output was realized. The transmitter was operating perfectly, though off frequency.  The tuning capacitor was adjusted (with full RF output) until the correct frequency was obtained, as noted on a nearby RCA Victor AM receiver.

Before regular programming could begin it was necessary to run a Proof of Performance. Frequency response was tested using an audio generator, and confirmed expected response from 100 Hz to 8 kHz, being down 10 dB at 50 Hz and 11.2 kHz.  Distortion was also checked ... it averaged about 5% throughout the pass band, rising to 10% at 100 Hz.

The lack of low-frequency response and excessive LF distortion was evidently caused by the limitations of the minute modulation transformer.

Noise performance was a bit disappointing.  The SN ratio was only 30 dB at best, referenced to 100% modulation. Most of the noise was low frequency hum; reversing the AC line cord in the socket helped only a few decibels.  Even shorting the audio input had little effect. I suspected an AC ground loop in the chassis ground connections.

Since the Knight transmitter would operate from AC or DC, we actually connected 110 V worth of batteries to the unit and powered it from pure DC. The hum remained.  I could only assume that there was RF pickup somewhere in the audio circuitry causing the problem. Other than that, the audio performance was respectable.

Modulation was adjusted via a front panel knob (violet knob with white dot) to a maximum of about 85%.

Connecting a speaker to the audio monitor output lowered this to 70%, evidently due to the limited power output capability of the 50C5 modulator tube

After the performance tests were complete, KGHL's regular programming began in the summer of 1964. It was very hot, yet the Knight-Kit transmitter performed flawlessly even with no cooling. Frequency stability was good, with less than 50 kHz of drift after a 30 minute warm up period.

Only after three years of constant use did a problem develop: the selenium rectifier stack failed, causing a loss of plate HV, and producing an overwhelming odor in the control room.

Repairs were made in a few hours, and the Knight-Kit transmitter has been on the air ever since. A few rust spots have appeared on its once-gleaming blue chassis, but the transmitter has been reliable for over 20 years.

Fly by Knight

Unfortunately, Knight Electronics has been out of business for several years, probably due to stiff competition from "the big boys."

There were several hundred Knight AM broadcast transmitters made in the '60s, some of which are still on the air today.  They are an excellent choice for many AM daytimers, especially those with low-power pre-sunrise operating authority.

Though a used Knight transmitter will command a high price, usually well over five dollars, checking RW's used equipment listing will be worth the effort if you find one of these fine works of engineering expertise.

At KHGL, we wouldn't have anything else. As the saying goes ... "'It' keep station profits high as a kite, you must be on the air, Knight after Knight!"

Jack Cheese is CE of KCHZ Powercheese Pario (formerly KHGL) and surfaces once a year on April Fools Day. His alter ego, Hank Landsberg is president of Henry Engineering and can be reached at http://www.henryeng.com/ and does not take kindly to the label "fool."

Reprinted with permission: Hank Landsberg Henry Engineering

A Zephyr, with  a sticker on the bottom gives instructions on using this “miniature broadcaster,” with which you play your records over your radio set. Can you tell us more about this?

A LINE-OPERATED ONE-TUBE RADIO (TRANSMITTER)

            Actually, I was looking over some different schematics for one-tube radios in back issues of the Horn Speaker, because I was intrigued by the idea that a radio could have just one tube.  All the other sets I'd seen at the club meetings and auctions had lots of tubes, and I learned these were to multiply the gain of the signal from the antenna, which is weak everywhere but in parts of Wheaton, Md. where I live.

     The set I chose to build used the circuit of figure 1, and it had an O1A tube.  Not wanting to get a five-volt battery to light it, I thought of using a cheaper tube and a 6-volt transformer from Radio Shack, plus I wanted plenty of gain, so I reworked the schematic to make the set play through a speaker!  That changed the design to the circuit of figure 2.  Little did I realize what a change that would actually make!

             I had all the parts but a breadboard - the guy at Radio Shack told me I could use another 6-volt transformer for the output transformer and proved it with an equation, and I also bought an isolation transformer the guy thought I might need.  He advised me not to use plastic solder and gave me some other tips.

            My antenna was a 50-foot length of wire strung around the corners of my workshop.  I removed all the insulation from the wire, too, so as to increase the gain.  When the circuit was finished, I turned on the power and was rewarded by the sight of a cheerfully glowing 6C4.  I also had a cheerfully glowing rectifier diode, until I reversed the polarity of the filter capacitor.  Finally, the set seemed to be working right, and I tuned the variable condenser (I think it's really a capacitor, too) looking for stations.

            All I had in the speaker was a low hum, so, deciding I needed more gain, I went back to Radio Shack and bought a 15 inch speaker.  When I hooked this baby up, things started to happen!

            It was this way: I had another radio on in the shop at the time, listening to Lush Rimbaud over WMAL, which is the only other station I gan get here in Wheaton so close to that 50,000 watt tower.  Suddenly there was a rhythmic sound coming from the radio that was like a crazed rhino crashing through the brush.  Lush never gets carried away like that, so I looked around for the source of this new interference. Imagine my surprise when I saw my dog Nipper sniffing excitedly at the new Radio Shack speaker - every time he touched the cone, there was another panting crashing sound from the shop radio.  Apparently my one-tube radio was actually working backwards, taking the noise of Nipper's sniffing and transmitting it over my new antenna to the shop radio.  I tested this theory by changing the tuning condenser of my set, and sure enough, the dog moved up in frequency to about 800 on the dial!

            I learned many things by designing my own radio using the circuit of figure 2.  I found out that:

            1.         A speaker can act like a microphone.

            2.         Radios have the property of reciprocity.

            3.         An isolation transformer can prevent a nasty  

          shock.

            4.         Capacitors can also be condensers, and some of

          them can be hooked up backwards.

            5.         If you have enough gain, you don't really need a

          ground these days.

            6.         When I connected my tape player to the speaker,

          the music came over every radio in my house!

            This last finding really hit me.  I had designed a transmitter.  That has to be harder than designing a receiver.  Now I use the circuit of figure 2 (and the isolation transformer) to broadcast music all over my house and I can also hear it in my Walkman outside! 

            Finally, I'm not completely sure about the finding of item 2 above.  I tried shouting into the speaker of every other radio in my house to see how well each one would broadcast, but got no result except with my own design.  Maybe it's because my workshop antenna has so much more gain.

                                                                        Dick Parks     April 1, 1993