1930's "homebrew" ham transmitter
When I started my career with IBM, one of my co-workers was a very interesting engineer, Marvin K. He was extremely intelligent and curious about many things, including astronomy, science, electronics and photography.
About a year after his death in 2004, his wife called me and said that she had a ham radio that he had built as a teenager and she thought I might like to have it. After I brought it home, I noticed that curled inside of the large copper coil, were several sheets of hand-written notes that described a lot about the construction and early use of this very basic radio transmitter. Typical of Marvin, the note was very detailed and contained a great deal of information about the radio. Here is his narrative....
"This is the short-wave amateur radio transmitter I built when I was age 13 in 1931-1932 in Sac City, Iowa. I operated under the call letters of W9AZA issued for the 80 meter CW band of 3.5 to 3.9 kilocycles per second (now called Kilo Hertz, or KHz, continuous wave, where the transmitter is keyed on and off with a telegraph-type key, using International Morse Code, NO voice operation)
This transmitter is a self-excited, push-pull oscillator, using two type ’45 tubes, where a heavy radio frequency current is generated, which oscillated back and forth at the resonant frequency of a tuned circuit consisting to two things: the large copper coil and the main tuning capacitor (or ‘condenser’). Energy is electromagnetically coupled to the two smaller copper coils which are connected to another tuning capacitor and the antenna system. This provides another resonant circuit which is tuned to the same radio frequency as the oscillator. Energy is then radiated from the antenna system…which was a zeppelin-type antenna with a 132 foot flat top, end fed with two parallel wires spaced 8 inches apart, one connected to one end of the 132’ antenna, the other one dead ended there..(not connected).
A separate power supply provided power to this transmitter. It consisted of a 115-volt AC power transformer, one type ’80 rectifier tube, two 8mfd, 450 volt filter capacitors, a filter choke and bleeder resistor. The transformer also supplied 5 volts AC for the ’80 tube filaments, 2 ½ volts AC for the ’45 tube filaments and 500 to 600 volts AC, center-tapped, for the nominally 250 to 300 volts DC for the transmitter tube plates. Plate power input to the transmitter oscillator circuit was maybe 20 or 30 watts, maximum. (I couldn’t afford voltmeters or ammeters which would have told me more...!) My radius of operation was Iowa and the adjacent states – seldom further.
My short-wave receiver was initially a 1 tube regenerative receiver I built and later a Super Wasp receiver, that my neighbor across the street had built and had replaced with a more up-to-date factory-built SW receiver. The Pilot Super-Wasp required a 6-volt car-battery for the tube filaments and a B- battery eliminator (connected to the 115 volts DC house current) for the 45, 90 and 180 volts DC the receiver used. It had plug-in coils to cover the 20, 40 80 and 160 meter amateur bands, as well as the broadcast band. It was regenerative also.
I operated mainly from 1932 thru 1940. The license had to be renewed, with proof of use, every 3 years or so. I finally let it run out….should have kept it active. My license was W9AZA, was a re-issue and came out when the W9K ---‘s (a very early call)...were coming out. My neighbor got W9KDL as the same time I got mine. He helped me, and we practiced code together via a telegraph line he installed between his house, mine and another 1 block away and one more a mile away..!
The plastic cover over the transmitter is not part of the original, but is just to keep the dust off. The cover, from an IBM type 650 scientific computer magnetic drum (circa 1955-1960) just happened to be the right size…!"
Photo info...shot with a Nikon D750 and Nikon 70-180mm Macro lens. Lit with a single Alien Bee and a gold reflector. This was a focus stack of a dozen exposures, all blended with CombineZP.
1930's "homebrew" ham transmitter
When I started my career with IBM, one of my co-workers was a very interesting engineer, Marvin K. He was extremely intelligent and curious about many things, including astronomy, science, electronics and photography.
About a year after his death in 2004, his wife called me and said that she had a ham radio that he had built as a teenager and she thought I might like to have it. After I brought it home, I noticed that curled inside of the large copper coil, were several sheets of hand-written notes that described a lot about the construction and early use of this very basic radio transmitter. Typical of Marvin, the note was very detailed and contained a great deal of information about the radio. Here is his narrative....
"This is the short-wave amateur radio transmitter I built when I was age 13 in 1931-1932 in Sac City, Iowa. I operated under the call letters of W9AZA issued for the 80 meter CW band of 3.5 to 3.9 kilocycles per second (now called Kilo Hertz, or KHz, continuous wave, where the transmitter is keyed on and off with a telegraph-type key, using International Morse Code, NO voice operation)
This transmitter is a self-excited, push-pull oscillator, using two type ’45 tubes, where a heavy radio frequency current is generated, which oscillated back and forth at the resonant frequency of a tuned circuit consisting to two things: the large copper coil and the main tuning capacitor (or ‘condenser’). Energy is electromagnetically coupled to the two smaller copper coils which are connected to another tuning capacitor and the antenna system. This provides another resonant circuit which is tuned to the same radio frequency as the oscillator. Energy is then radiated from the antenna system…which was a zeppelin-type antenna with a 132 foot flat top, end fed with two parallel wires spaced 8 inches apart, one connected to one end of the 132’ antenna, the other one dead ended there..(not connected).
A separate power supply provided power to this transmitter. It consisted of a 115-volt AC power transformer, one type ’80 rectifier tube, two 8mfd, 450 volt filter capacitors, a filter choke and bleeder resistor. The transformer also supplied 5 volts AC for the ’80 tube filaments, 2 ½ volts AC for the ’45 tube filaments and 500 to 600 volts AC, center-tapped, for the nominally 250 to 300 volts DC for the transmitter tube plates. Plate power input to the transmitter oscillator circuit was maybe 20 or 30 watts, maximum. (I couldn’t afford voltmeters or ammeters which would have told me more...!) My radius of operation was Iowa and the adjacent states – seldom further.
My short-wave receiver was initially a 1 tube regenerative receiver I built and later a Super Wasp receiver, that my neighbor across the street had built and had replaced with a more up-to-date factory-built SW receiver. The Pilot Super-Wasp required a 6-volt car-battery for the tube filaments and a B- battery eliminator (connected to the 115 volts DC house current) for the 45, 90 and 180 volts DC the receiver used. It had plug-in coils to cover the 20, 40 80 and 160 meter amateur bands, as well as the broadcast band. It was regenerative also.
I operated mainly from 1932 thru 1940. The license had to be renewed, with proof of use, every 3 years or so. I finally let it run out….should have kept it active. My license was W9AZA, was a re-issue and came out when the W9K ---‘s (a very early call)...were coming out. My neighbor got W9KDL as the same time I got mine. He helped me, and we practiced code together via a telegraph line he installed between his house, mine and another 1 block away and one more a mile away..!
The plastic cover over the transmitter is not part of the original, but is just to keep the dust off. The cover, from an IBM type 650 scientific computer magnetic drum (circa 1955-1960) just happened to be the right size…!"
Photo info...shot with a Nikon D750 and Nikon 70-180mm Macro lens. Lit with a single Alien Bee and a gold reflector. This was a focus stack of a dozen exposures, all blended with CombineZP.