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AM Receivers

  • 10A AM receiver schematic. 1934. 848k. Scanned by Stanley B. Adams

AM Transmitters

  • Technical Bulleting T-670, 1923. Describes the 101-A and 102-A radiotelephone broadcasting systems. The 101-A uses a 1-A 500W transmitter. The 102-A uses a 2-A 100W transmitter. Each system includes motor-generator power supply, 1A speech input amplifiers, and 2-C radio receivers. The receivers are used to comply with radio regulations requiring periodic monitoring for distress calls. Scanned and comtributed by Timothy Hughes. 8MB.

* The DOHERTY Amplifier - Approx 1942. Booklet describing the Doherty amplifier.* Gives a brief description of the theory behind the Doherty amplifier. Includes letters from WHAS, KTUL, KQW, and KRLD. Contributed by Randy Kerbawy. See also A New High-Efficiency Power Amplifier for Modulated Waves , Doherty's original paper on the Doherty method of generating AM. Additional photos of WHAS (as mentioned in the WE booklet) are available. These photos are posted by Scott Cason.

* 310-A and B Radio Telephone Broadcasting Equipment* -100 to 250 watts- by Stanley B Adams

* Continental Electronics 105C One Mega Watt Medium Wave Transmitter*. The Continental Electronics 105C very clearly shows the Weldon-Western Electric lineage. This is supposedly the first mega-watt medium wave transmitter in the world. While there are slight circuit differences and some tube differences, please note that this is a linear based transmitter that uses the Weldon modified Doherty circuit. This was supplied through the courtesy of David Hultsman of CCE and scanned by Stanley Adams. CCE 105C

*Audio Equipment

*FM Transmitters

  • 504A-1 Synchronized Frequency Modulation Radio Transmitting Equipment, 3000 Watts, 42 to 50 Megacycles. This brochure describes the 504A-1 FM transmitter that operated in the "original" FM band. Synchronized frequency modulation refers to the unique automatic frequency control.

"In synchronized frequency modulation, the total number of cycles is, in effect, counted, compared with the number of cycles generated by a precise fixed frequency standard, and the tuning of the variable oscillator adjusted mechanically to keep the two always at exactly the same value." The carrier is divided by 8,000 and compared with a 5kHz reference crystal oscillator.

One added note by Stanley Adams, this pre-war 'box' also served as the basic design when FM 'cranked up' after the end of WW2. The synchronizing circuit consisted of a motor that was modulated by the error voltage between a crystal standard and the 'countdown' chain. This would vary a capacitor in the exciter. A number of stations replaced this 'mistake' during the early 50's with units devised by companies such as Harkins Electronics of Phoneix, Arizona. This was a serrisoid type of exciter and much more stable.

*Vacuum Tubes


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