Wednesday, June 8, 2011

My Trip To Little Rock: Tuesday, More Technoid Stuff

I can't even be able to convey in words how I personally felt, being not only at the transmitter site, but being able to actually touch and examine the circuits that flung those beautiful radio signals practically halfway 'round the earth!

I sent a few photos to Dave Montgomery and asked for comments, since he, as well as Felix, knew the transmitter in and out.  First the pictures, then Dave's comments:

"This is the high voltage rectifier "stack". These parts converted the AC power incoming from the power company to a very high voltage DC that was used in the high power modulator and RF amplifier sections of the transmitter. The original configuration was two rows of mercury vapor rectifiers - one tube can be seen in place in the photo. The other tubes have been replaced / updated with solid state versions that, theory, "never" burn out. If my memory serves me, we ran about 10,600 volts DC at about 5.6 amps for the final power amplifier . If you calculate this out, you see it is about 59,000 watts +/- - - transmission line losses and other factors reduced this to right at 50,000 watts at the tower."

"This is the rear view of the modulator cabinet. The modulator was where the audio from the studio was amplified many times over up to the equivalent of about 35,000 watts (!!). On the left side you can see the two power amplifier tubes (the round thing with the RCA emblem on it). On the right you can see the intermediate modulator amplifiers which boost the relatively tiny studio audio signal up to a signal compatible with the two big power amplifier tubes.

One thing that was nice about this transmitter was that RCA placed all components in the open, which allowed easy inspection and service when needed. Time was always the essence, so they made it very easy to work on when necessary.

One thing not in this picture is the modulation transformer. The transmitter's modulation transformer was a huge oil-filled steel tank with the transformer inside. It weighed about 7,000 pounds and was the single largest component in the transmitter. It was truly one of a kind. If it ever failed for any reason, there were no spares except in other transmitters. To replace it would also have required a partial demolition of the transmitter itself to make room for the lifts, cranes, and other heavy lift equipment working in a confined space."

(Probably one of the transformers in other pictures?  bs)

"This the antenna relay. Its function was to connect the transmitter to the towers, and to switch the transmitters between the daytime and nighttime tower configurations.
The building has a main transmitter and a backup transmitter, and each one had to be capable of being switched between the daytime antenna and the nighttime antenna configurations. That is what this switch does. If you look closely you can actually see three distinct relays in the photo. You can also see the two transmission lines (the copper "pipes" near the top of the photo). One of these transmission lines was used for the daytime antenna (all power goes to the single center tower). The other transmission line goes to the night time antenna configuration, which was three towers. During night time operation, the 50,000 power was split three ways, with some power going to each of the three towers."
(I'd wondered how that worked!  bs)
"This is the transmitter final power output cabinet. Inside you can see the RF (radio frequency) power amplifier tubes in their sockets. The coils are used to tune the final RF amplifier section to the antenna load. At the top of the photo you can see where the radio signal feeds through an insulator to the antenna relays mounted on top of the cabinet. When the RF left here, it went into the towers and on its way to thousands of listeners."
And there WERE thousands of listeners!  There was so much going on behind that dial we never knew of, more than we could ever imagine.  So much high-quality, beautiful circuitry goes into a radio transmitter, hardly anyone who visits a station ever gets this treat of seeing where the heart is!
More of Dave's tour later- stay tuned!
Bud S. (

1 comment:

  1. Dear readers and visitors, Dave Montgomery sent this message to me, with permission to use it as a comment:

    "Felix was singularly the most knowledgeable of the transmitter, how it worked, and how it sometimes misbehaved (which was not very often). My main role and responsibility was at the studio on West 7th street and later on at Cottondale Lane. My transmitter commentary is simply what I was able to learn (and remember-??) from Felix during my trips to Wrightsville, and his patient teaching of what did what. What I learned was a rudimentary understanding and nothing more than that - but I thank you for your compliment.

    Tom Rusk was for a long time Felix's assistant at the transmitter, and he frequently cast the life preserver when one of the wheels ran off the road. Tom deserves high recognition for his work in maintaining the transmitter alongside Felix."

    Thanks, Dave! Bud S.