CCA Transmitter Simplifies Rebuild
By Robert F.Ritchey
Engineering
Consultant KDRY (AM)

SAN ANTONIO In the summer of 1992, KDRY (AM) in San Antonio hired me to rebuild the station's transmitting plant and antenna system. The scope of the project convinced me that CCA AM transmitters are viable alternative to the products from the big-name companies that dominate the industry . During the early 1980's KDRY's owner upgraded power a number of times, from IkW eventually to 11 kW. The station also added 1 K w at night with a directional antenna system. The rapid succession of upgrades stretched the capacity of the station's two 30-year-old Collins Radio E series transmitters. In an attempt to reach the llkW power authorization, one transmitter was field modified. At best, it was able to generate only about 9kW, and no further modifications were possible without raising the costs too much.

Maze of relays
To further complicate matters, a second Collins E series transmitter was used for directional nighttime operation. A maze of RF relays was used to switch between transmitters when the station changed power and pattern.
I recommended replacing the main transmitter immediately. A single unit could perform both daytime and nighttime power functions, eliminating some of the RF relays and the switching network. Also, anew transmitter could achieve higher levels of modulation with a distortion-free, clear audio signal.
KDRY's need for a medium power transmitter coincided with a shift in technology at the major manufacturers. Solid state RF stages were coming on-line and older designs were being "built-to-order” with long delivery dates. Goos, late-model used transmitters were nonexistent.
Steve McElroy at the CCA plant in Fairburn, Georgia had a 10,000D series unit in stock and ready for shipment. At first, I had reservations about purchasing an unfamiliar transmitter. But a visit to the Fairburn plant to see the transmitter in operation allayed my concerns about product design and durability.

Convenient features The transmitter is well built, with easy access to major components. Most parts are standard and are readily available through commercial parts dealers. Interconnecting cables are clearly marked and easy to access. Opening the rear doors allows visual inspection of the power supply, chokes, transformers and caps. The modulator feedback ladder is mounted at eye level on the rear of the modulator cavity. An important consideration in deciding on the CCA transmitter was an impedance difference between the KDRY daytime and nighttime patterns. Many of the solid state transmitters available at the time were experiencing problems with rapid changes in load impedance. KDRY programs a religious talk format and down time, for any reason, is a serious matter. The CCA transmitter copes with the impedance change and requires only a modest amount of remote adjustment by the operator on duty to maintain proper tuning. Once un-crated, less than 30 minutes were needed for visual inspection and to complete the necessary internal connections before AC power could be applied. CCA recommended a closed delta, AC configuration, for the 10,000 series transmitters; however, we ran the unit for several months in an open delta arrangement. There was no appreciable difference between the two configurations.

Flat audio response
Audio response for the CCA transmitter is essentially flat. Two proofs performed over an 18-month interval indicated a variance of less than 1 dB from 50 to 10,000 Hz. Overall distortion was less than 1 percent.
The RF final employs a 4CX15000 tube operating as a plate modulated class C amplifier. The size of the tube affords the CCA 10,000 the capability to sustain a fullllkW output at or close to lOO percent modulation.
I am delighted with the performance of the CCA 10,000 series transmitter. My only concern is the anticipated cost of replacing the final. So far, the final delivered with the unit has logged more than 9,000 hours of stable emission without any appreciable sign of wear.
I recommend serious consideration of the CCA AM
transmitters. They are stable, simple-tomaintain and cost effective to operate in difficult environments, such as the
changing load impedance in the KDRY directional system.

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