Knight Kit Home Broadcasters - Allied Electronics
Home ] Up ]



Builds a Wireless Broadcaster-Amplifier

June 1959 With permission
Flexible Knight-Kit transmits music throughout the home
(For the  full graphics scan of this article including the schematic scroll down)



The Knight Wireless Broadcaster-Amplifier, (Allied Radio Corp. 100 N Western Ave, Chicago 80, Ill.), takes only a few hours to build, and has many home entertainment uses It can be connected to a record player, or microphone to send programs out to any number of standard radios in the house. 0r it can be used a, a complete preamplifier, and amplifier, with any phono cartridge One input takes ceramic or crystal cartridges and microphones; the other takes magnetic cartridges and microphones.

Mounting of the major, parts or the unit is the first assembly step. There is a good reason for this because all the parts mounted on the underside or the chassis have terminals that are used for point-to-point wiring.  Sockets. input jacks, volume control and switch. selenium rectifier and terminal strips are involved here. Parts with wire leads are supported by those leads after they are soldered into the circuit. There are 72 steps in all to be followed In competing the broadcaster-amplifier.

How It Operates The phono amplifier, section consists of Two tube.; a " and a 50C5 This circuit amplifies the Input signals from the phono cartridge or microphone. making the signals strong enough Io drive a speaker,. Output is slightly more than 1 watt.

Ceramic, crystal or magnetic cartridges are correctly loaded by Input resistors The , preamplifier' tube supplies the high gain needed for magnetic cartridges with equalization supplied by a feedback loop made up of R-6 and C-4 In the circuit.

Output from the preamplifier stage is fed Into the 50C5 audio output lube which supplies ample power to drive a 3.2-16 ohm speaker. The output level is adjusted by a volume control at the grid of the output tube.

As a wireless broadcaster. this unit operates much like a regular broadcasting station. It sends out a modulated carrier signal between 600 and 1500 kc which can be received by any standard radio within its range.

The carrier wave is produced by the 50C5 oscillator tube, and can be varied between 600 and 1500 kc. by adjusting a trimmer capacitor, whose screw projects through the top of the chassis. The audio 50C5 doubles as an audio output and modulator lube. and amplifies the audio voltage to effect 75% modulation of the carrier wave.

Clean modulation is assured by the use of degenerative feedback The amount of modulation can be varied by adjusting the percentage control.

Remember, that the wireless broadcaster transmits a signal over the air, and hence must meet FCC requirements to be operated without a license. It it is built according Io the Instruction manual, with not more than 10 feet of antenna connected, there will be no problems. The FCC requires that the certification listed on page 15 of the Allied instruction book be attached to the unit. Cut it out of the manual and paste it on the bottom cover,.

Modifications For more advanced experimenters, or beginners who have conquered the fundamentals the Allied broadcaster circuits can be modified very simply Io form other pieces of equipment. For example. you can change the oscillator circuits Io cover a very low frequency Io make a wired-wireless or carrier-current transmitter that will radiate over the local power lines Io a considerable distance.

An audio signal tracer is another piece of equipment that can be made from the unit. Almost no modification is needed, but an isolation transformer should be added since you may use to to test audio amplifiers or receivers that have an ac/dc. circuit. Only the 12AX7 and one of the 50C5 tube are employed for, signal tracing. The r.f. oscillator 50C5 is not needed but its filament is required In the circuit. A switch can be added Io open the cathode circuit to make the oscillator Inoperative.

All under-the-chassis wiring is completely enclosed and rubber, feet are supplied so that the unit can sit on lop of any piece of furniture AC. leakage from chassis Io ground is said Io be well within Underwriters Laboratories specifications. The finished unit can be proudly displayed, or-if concealed location is preferred -it's small enough to fit almost anywhere.



Since High Voltages are used, these transmitters should only be built by experienced people, or under the supervision of experienced people.  

- ed sharpe


The Knight Kit Wireless broadcaster
as reviewed in Popular Electronics  By Otto Fried  May 1955
 With permission


This was the first version of this broadcaster offered by allied electronics and did not  have the Speaker output as the second unit  that was called the Knight Wireless Broadcaster-Amplifier. This  first model did not have a fully enclosed chassis and  could be quite dangerous. 


Since High Voltages are used, these transmitters should only be built by experienced people, or under the supervision of experienced people.  

- ed sharpe



wpe14.gif (469837 bytes) wpe1C.gif (384362 bytes)

wpe17.gif (353581 bytes) wpe1A.gif (71583 bytes)
Click on small picture to make larger

Knight Wireless Broadcaster-Amplifier
as reviewed in Popular Electronics    June 1959
With permission


This is the second version of this Kit that was introduced.  This unit featured the  ability to use it as a  audio preamplifier/power amplifier in addition to the function provided by the earlier unit as a wireless broadcaster over an AM radio.  The Second version  featured a fully enclosed chassis thus preventing wandering fingers from entering the electronic circuitry from the side of the chassis! 


Since High Voltages are used, these transmitters should only be built by experienced people, or under the supervision of experienced people.  

- ed sharpe



wpe10.gif (318623 bytes) wpe12.gif (360941 bytes)
Click on small picture to make larger

Thanks to  Rich - KB8TAD for  assistance with scans and info.


Since High Voltages are used, these transmitters should only be built by experienced people, or under the supervision of experienced people.  

- ed sharpe



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 and does not take kindly to the label "fool."

Reprinted with permission: Hank Landsberg Henry Engineering


From 1964 Allied Radio Catalog
Thanks to Hank Landsberg Henry Engineering


1510 AM On Your Radio Dial with Knight Kit Broadcaster!

Submitted by: George Laurie, Dover, NJ

George Laurie

In 1961 I became very interested in radio broadcasting after visiting several local
radio stations in my area. I developed a technique where I ran a hot-wire from the
output mixer of my make-shift studio (in my attic) with two turntables, a tape
recorder and a mike to the aux input of an old radio downstairs in the living room.
Every evening, my family got to listen to me on-the-air, or at least I thought they
were listening.

One day I came across an ad advertising the Allied-Knight broadcasting kit and all
my dreams came true. Finally, actually going on-the-air with live broadcasting.
After everything tested OK, my cousin and I built a studio in my basement and went

As it is with all owners of a radio station, the power output was never good enough.
Finding out my signal hardly went beyond my neighbors house, I found out the longer
the antenna wire, the better the signal range. Running my antenna wire from my
basement to the top of my house, I found I had at least a two-mile range. WOW! This
was great!

Every summer during my early high school years we ran a full schedule of
broadcasting from morning until early afternoon. Top hits of the day during the
morning hours, jazz at lunchtime and MOR during the afternoon. Our Knight
broadcaster carried a good quality, clean sound that even had some of my neighbors
listening to us. Eventually, I purchased a second Knight transmitter as a backup and
began to alternate between the two.

If I remember correctly, we used a 1956 Revere Reel to Reel tape recorder,
an old three speed phonograph which we found or was given to us and a
Silvertone Automatic Changer HiFi set which was given by my brother. The
Silvertone always gave us a problem because many times when we were ready
to release the record to spin over the air, the automatic changer would
kick in and lift the arm off the record, attempt to drop the next record
and move the arm back onto the record. This is where we learned the art
of ab-libing until the process completed. After awhile, we were able to
master this inconvenience.

For output sound, we used alligator clips to tap the speakers on the
record players and used the output plug on the tape recorder. We twisted
these three wires together onto the input wire going into the transmitter.
Many times we would loose sound because one of these wires would come off
or touch together. Never solder, but we did learn about electrical tape.

Our tower wire was about 50 to 60 feet long and ran from my basement to a
small pole on the top of my roof. That seemed to put out a adequate
signal for us, up to 2 or more miles. We were extremely happy about
reaching such a large audience. Although we never conducted any surveys
to find out how many people were listening.

My cousin Roger would sign on around 10 am until noon. We had a one hour
taped lunch time program and I came on from 1:00 until 3:00. Many times
we never made it til 3:00 because on nice days it was time for swimming or
baseball. On rainy days, we would expand our broadcasting times.

Yes, the Allied-Knight broadcaster was the greatest invention ever made!

Cousin Roger

One day I read in the newspaper about an illegal radio station broadcasting at a got
busted by the FCC in Atlanta, GA and faced a possible $10,000 fine and 5 years in
jail. Now we became very paranoid about our broadcasting activities.

One morning when we signed on-the-air, we heard a loud hum coming over our 1520
frequency and thought we got caught by the FCC. We shut everything down, took our
studio apart and hid our transmitter. It wasn't long after that, that we realized a
new radio station was going on-the-air at 1510 and they were performing tests. After
that, we never did go back on-the-air.

Now attending college, my broadcasters followed me and for over a year, we ran an
out-of-control campus radio station until the school shut us down and started their
own campus radio station which they had complete control of.

For the next 25-years I became a professional broadcaster working in all sorts of
radio stations, both large and small. PD, MD, overnights, news, MC, spots, promos,
engineer (First Class License), you name it, I did it. I loved every minute until I
got married and one day my new wife reminded me, I wasn't making any money. The rest
is history.

I still have my two Knight Broadcasters in working condition. There is a nearby museum
that I will use them up to  put radio programming on AM into old radios that are on  display.




Everyday we rescue items you see on these pages!
What do you have hiding in a closet or garage?
What could you add to the museum displays or the library?



DONATE! Click the Button Below!

Thank you very much!


Material © SMECC 2007 or by other owners 

Contact Information for
Southwest Museum of Engineering,
Communications and Computation 

Talk to us!
Let us know what needs preserving!


Postal address - Admin. 
Coury House / SMECC 
5802 W. Palmaire Ave 
Glendale, AZ 85301 

Electronic mail 
General Information: