[BC] when you had to bunk at the station

[RichardBJohnson at comcast.net]

The RBJ-1C: Most would think that it was rather conventional nowadays. However, that was because it was copied by many other broadcast transmitter companies and they got the press. Note that everything that was Type Accepted was required to have all of its design data open for public inspection at the FCC office in Washington, DC. If you wanted to see the "latest and greatest" design details, you just went to Washington. There were no secrets.

Final amplifier (2) 4-400A Parallel
Modulator       (2) 4-400A Push/Pull
RF driver 6146
RF buffer 12BY7
Crystal Oscillator 12BY7
Modulator driver (2) 12BY7
LV rectifier 5R4
Screen rectifier (2) 866
HV rectifier (2) 816
Voltage regulator for crystal oscillator 0C3

In those days, most all 1 kW transmitters used 833-A tubes. Collins had just made a 500-watt transmitter that used 4-250A tubes and RCA was working on a BTA1-R, which was to use 4-400A tubes, but it was not available yet.

The 12BY7 was the "video amplifier" tube used in most TV sets. It was ideal --nothing better.

Eimac anticipated that the tube of the future was going to be the 4-400A so they GAVE me four tubes plus four sockets. They really wanted this transmitter to be a success! Eimac's technical input was to dissuade me from operating the finals in push-pull, which was my original design.

The transmitter had several notable features. The most notable being that it was the first Type-Accepted broadcast transmitter to not require a crystal heater. Practically all the broadcast transmitter companies used the red RCA crystal unit with the 120-volt thermostatically controlled oven. The FCC it seemed, considered the crystal as the "heart" of the transmitter so practically nobody wanted to mess with something that had already been approved. I did not know that so I got a new company, Northern Engineering, of Burlington, Iowa to give me a crystal for 1570 kHz (WDEW's frequency) and a recommended schematic. They were supplying precision crystals to manufacturers of military equipment. Eventually, these vacuum-mounted AT-cut crystals became the standard of the industry.

The power supply "iron" was wound by Campbell Electric of Lynn, Massachusetts. I designed the transformers and reactors using standard design charts. I provided actually winding data, i.e., coil-build, etc. http://www.electrotherapymuseum.com/Campbell.htm Initially I was going to use a UTC "polypedance" transformer for the modulation unit. http://www.bunkerofdoom.com/xfm/UTC_1955_WEB/025.jpg

I drove from Westfield, Massachusetts to 450 Varick Street in Brooklyn to pick it up. It was so "special," promised such high quality. It was crap. It barely passed speech audio, much less its advertised high fidelity. I was overwhelmed. Don Howe from Worcester Polytech said, "Just design a transformer and have Campbell Electric wind it." Therefore, I did! By guess, gosh, and golly, it turned out to have exceptional frequency response and distortion characteristics. Two "secrets" to making modulation transformers: (1) use lots of iron and little copper. (2) High frequencies stay on the outside of the coils.

Don Howe was a well-known Northeast radio consultant whose day job was teaching at WPI. He made the measurements for FCC type-acceptance that required equipment that I did not have. He did not cheat, either. My initial final amplifier output network was a PI-L because that is what "everyone" used. It turned out that "everyone" cheated. We needed a PI-T to get required harmonic attenuation.

The transmitter was a success. However, Johnson Associates was not. The first transmitter went to WDEW in Westfield, MA, which paid for its construction. The second went to WFGM in Fitchburg, MA. They sold the station before the transmitter was paid for and I was never paid. This was my first rude awakening to the cruel business world. It took me several years to pay for the components I had purchased to make that transmitter.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Dave Hultsman" <DHults1043 at aol.com>

In a message dated 4/7/2010 5:33:20 PM Central Daylight Time, RichardBJohnson at comcast.net writes:
>but I wasted it designing a transmitter, the Johnson Associates RBJ-1C.

Tell us more about the RBJ=1C Transmitter.
 
Thanks
 
Dave Hultsman