Am transmitter site – Page 18

General Electric BT-25-A

This is one of my favorite old transmitter memories. Back when I landed my first Chief job, I was working for an AM/FM combo. The AM station was a 50,000-watt flame thrower that first went on the air in 1947. The original transmitter, a General Electric BT-25-A was still in service as a backup unit. These pictures are from the last night it operated, December 16, 1993. The bank made us remove all of the PCB transformers and capacitors before they would refinance their loan. Of course that was most of the transmitter, the rest of it was scraped or sold for parts.

This is a long transmitter, GE BT-25-A looking from the control cabinet

The transmitter takes up the entire span of the room. There were eight large cabinets, each with its own stage or section. The stages were connected to each other by a wiring trough in the floor. The transmitter used lead-jacketed cable within and between sections.

IPA stage with "multi-meters" — IPA stage with “multi-meters”

The IPA section had been modified to use 833A tubes. This is where the RF was developed and amplified for the final section. It is in the middle cabinets of the transmitter, the audio and control section being to the left, the PA and PA power supply being to the right.

PA section. Those WL 5891 tubes. — PA section. Those are WL 5891 tubes.

Final section. There were three tubes, only two were in use at any given time. The third tube was a spare which could be quickly placed in service by throwing a knife switch and moving those bars on the back wall around. This picture was taken with filament voltage only, we had to close the door to turn on the PA voltage.

The transmitter was cooled by this blower which faces down into the floor. Concrete duct work carried the air to the various stages of the transmitter. The blower is powered by a 2 1/2 HP motor. There were two blowers, one in use and one in standby. Behind this is an air mixing room and filter room. During the winter time, the transmitter waste heat was used to heat the building by closing a series of ducts and opening other ones.

Modulation transformer and modulation reactor

This is in the transformer vault. The unit to the left is a modulation transformer, it was 7 feet tall. Directly in front is the modulation reactor and just out of the picture to the right is the plate transformers. The plate supply was 480 volts 3 phase. The other piece of green equipment is a hydraulic tube jack, to get the 5891 final and PA tubes out of their sockets.

The transformers were what contained most of the PCBs. The modulation transformer contained about 150 gallons of Pyranol, the GE trade name for their transformer oil. Pyranol contained greater than 750,000 parts per million PCB.

It is a shame we had to kill this transmitter, it sounded wonderful on the air. The day we signed it off, there was nothing like it, not the Mw-50B that replaced it, nor the Nautel ND-50 that replaced the MW-50, nor the DX-50 at the competing station across town.

What a shame.

Underground Electrical feeder burn out

In the never-ending saga of things I have not yet seen, we had a 350 kcml 3-phase underground feeder burnout yesterday at our AM transmitter site.

Actually, it happened the day before, around noon. I received a call from the remote control that we were on the backup generator. Upon arriving at the site, I found several trees down on the three-phase primary down the street. I figured that was the cause. After checking the generator fuel supply, oil pressure, temperature, phase volts/amps, I decided that everything was okay and the power company would be along shortly to restore power. I then continued up the road to our FM site to do weekly maintenance.

Upon returning to the office several hours later, I looked at the utility company’s website. They have a pretty cool interactive map application that shows all outages and give restoration times. The area around our transmitter site showed no outages, therefore I figured it had been cleared.

I committed two errors here:

Not calling the utility company myself to ensure that the outage was reported. I assumed that the tree across the three-phase primary was the cause, it was not.
Not calling the transmitter site remote control to check the generator status after I checked the website.

To be honest, I don’t know if I am coming or going these days. With seven radio stations, each with its own transmitter site, three of them Directional AM stations, and three studio locations spread out over a 75-mile stretch, it is difficult to keep up with the small details. Did I mention that I am solo, the engineering assistant position was cut two years ago. But, I am not here to make excuses…

The net result is the generator ran all night long. The next day, when I checked the transmitter in the morning, I was surprised to find the generator still running. Unfortunately, I had an FM station on low power (see post below) that needed to be taken care of first. When I finished replacing the RF module in the FM transmitter, I made my way to the AM site.

I called the power company and then checked the generator fuel, the propane tank was down to 10%. Yikes, better get this taken care of fast. I will say the power company showed up pretty quickly. After some measurements with a handheld meter, it was determined that the underground feeder was open between the pole and the transmitter building.

The lineman was not at all surprised, in fact, he called it before he even went up in the bucket truck. After some back and forth with his supervisor, who came out in a pickup truck, it was decided that they would run a temporary overhead feed to the meter can.

They also did some research in their records and discovered that they (the utility company) own the underground cable and therefore they would dig it up and fix it. That’s nice because otherwise, it seems like it would be an expensive repair job. On a station that makes not have a lot of money.

Tower down

You know it is going to be a bad day when:

a farmer mowing grass took a wrong turn on June 16, KFEQ AM lost a guy wire and eventually one of its four towers came toppling down

From Above Ground Level magazine.

Is hiring the farmer down the road to come and mow the AM field a smart thing to do? It depends, I suppose, on whether or not your towers will be standing afterward. Hopefully, the guy had some insurance, if not then the station is basically screwed. The article did not mention that, although it did state that “The station is weighing its options,” Which does not sound good.

The good news is at least they were doing the maintenance. Most AM stations these days don’t even bother to mow the fields. Look at this picture:

Tall grass at an AM transmitter site. Owner says don't cut it. — Tall grass at an AM transmitter site. Owner says don’t cut it.

It is not that I don’t want the grass cut, I do. However, I am not going to pay for it out of my own pocket, that is ridiculous. So, it grows.