[BC] Frequency Control

[RichardBJohnson at comcast.net]

Earl Hewingson made a transmitter for WTYM, East Longmeadow, MA. It ran 5 KW (sic) on 1600 KILOCYCLES (sic). It occupied the entire basement and it was a work of art, built into individual screen-rooms. The "Frequency Generation Set" was in its own room. It consisted of a circuit constructed on metal plate within a wooden temperature-controlled box. The circuit used a 6SA7 for the oscillator and a 6CA7 buffer. The oscillator tube had been developed as a "pentagrid converter," however it has outstanding isolation between its input and output because of the grids. It was Hartley-connected. The interior of the box was temperature-regulated using proportional control with a 6SN7 and four 6L6 tubes! The temperature regulator was much more complicated than the oscillator. Its circuit was "borrowed" from some Western Electric Navy transmitter I was told. Western Electric also made the crystal. It was pressure-mounted in a four-pin ceramic housing that took many hours to stabilize.

This was an example of how "frequency control" was done in the "olden days." In fact, the quartz crystal was considered the heart of the radio transmitter. It was so "protected" that a composite transmitter was not allowed unless certain standard circuits and devices were used! Later, RCA was able to capitalize on this because they made a "FCC certified" crystal control unit that many transmitter manufacturers were forced to use. The WTYM transmitter was designed before RCA had a chance to take over the industry.

Although the WTYM transmitter design was very old, it was when I first saw it, that I knew that I could make a FCC Type Accepted transmitter -as a teenager!

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

----- Original Message -----
From: "Barry Mishkind" <barry at oldradio.com>

At 11:56 PM 11/11/2010, harold stanton wrote:
> When all this began, please remember that true single frequency control had yet to be developed.
> Operating "close" to your "assigned" or chosen wavelength was done with a free-running oscillator.

        The history of broadcasting includes 
        how the RI would come in and make 
        a mark on the front of the transmitter, 
        showing where the proper frequency 
        was located.