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
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 where 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.

air cooling blower
air cooling blower

The transmitter was cooled by this blower which faces down into the floor.  A 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 is 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
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 where 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, is 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.

Cold War Relic, ATT long lines microwave site Kingston, NY

Once upon a time, in the not too distant past, all long distance communication in the US was handled by one company, AT&T. There was no other company that could transmit data over medium to long distances. The breath and scope of their communications network is not understood by most people these days. Most people know that AT&T handled long distance telephone calls for the Bell Telephone System until the Bell breakup in 1984. However, AT&T did a lot more than long distance phone.

For example, if you watched the network news or network TV show anytime before 1980, it was likely brought to you via AT&T microwave system, known as AT&T long lines. Listen to the news on the radio, same deal. Before the wide spread use of communication satellites and fiber optics, the AT&T microwave relay network was the only way to get various types of electronic media signals from one place to another.

Beginning in the late 1980’s, competing local and long distance telephone companies began installing fiber optic cables between company offices. That coupled with the increased use of satellite systems for mass media video and audio delivery services made the huge AT&T microwave network obsolete. Some of the old microwave sites that are located in down town areas have been reused by local phone companies and cell phone providers. Many of the rural sites now sit empty.

ATT long lines microwave site with towers
ATT long lines microwave site with towers

This is the former AT&T microwave relay site located near Kingston, NY. It is now owned by American Tower, Inc. There are two towers behind the building, only the tower on the right has a few active communications antennas on it.  The taller tower is 190 feet tall and was built in 1957.  The shorter tower is 120 feet tall and was built in 1961.  Both towers and everything on them was made by Western Electric, the same company that manufactured the telephone sets.  Chances are, Western Electric contracted the actual manufacture of equipment out to others, then billed AT&T, their parent company a markup.  Something that would make all MBAs proud.

Western electric 190 foot tower, built in 1957
Western electric 190 foot tower, built in 1957

This tower was built in 1957.  The structure and galvanizing are still in excellent condition.

The large antennas you see on the towers are microwave horn antennas. They are no longer in use. Several transmitters and receivers would have been connected to each one of these antennas by use of RF multiplexers. Each microwave transmitter/receiver would have had several data channels. Generally, this was C Band microwave equipment, so it was in the 4, 6,  and 8 gHz frequency range.

Western Electric KS-15676 microwave antenna
Western Electric KS-15676 microwave antenna

All of this telephone traffic was transmitted on digital data channels un-encrypted. Many have argued that this allowed the government (most notably the NSA or National Security Agency) to intercept and listen to most domestic long distance telephone calls within the US. There is a book called Puzzle palace by James Bamford if you are interested in NSA history. It was written more than 20 years ago, so it doesn’t really apply today, but it is an interesting look at what the government was up to.

The building itself is huge, the first floor is 16,000+ square feet and the second floor is 10,000+ square feet. Only about 1000 square feet of this space is actively being used.

I believe this building was built in the late 1940’s or early 1950’s, just as Kingston was growing into a major IBM manufacturing site. It has remnants of the ATT coaxial based system that was used prior to microwaves.  The IBM buildings are located a few miles to the south east of this location, they are another cold war relic for discussion later. The IBM buildings were a major computer research and development site in the 1950’s until it closed in 1992. It was assumed that the Soviets had several spy satellites trying to steal secrets from the area, and the IBM facility was a primary nuclear target.

Blast baffle for generator cooling air intake
Blast baffle for generator cooling air intake

The microwave relay site has 12 inch re-enforced concrete walls. The ventilation air intakes have blast baffles to prevent a pressure wave (from a nuclear explosion) from blowing the ventilation equipment off of its mounts.

pnumatic actuator panel, seals all outside openings with steel blast doors
pnumatic actuator panel, seals all outside openings with steel blast doors

All of the outside openings were able to be sealed with steal blast deflectors using a pneumatic control panel located in the control room. There was a five minute timer, presumably to allow the HVAC units to be secured before the doors where closed. They where heavy gauge steel shutter designed to deflect the pressure wave of a nuclear explosion. Since this is an earlier building, it is likely that it is built to a 2 PSI pressure wave spec.  Newer buildings were built to 20 or even 50 PSI.  This microwave relay site would not have withstood a direct hit from a nuclear warhead, especially the higher yield warheads that came later on.

Water chillers for HVAC system
Water chillers for HVAC system

There where three large water chillers to provide cooling to the HVAC units. Since this was the 1950’s all of the electronic equipment would have had tubes, which would have generated a lot of heat while operating. There were two loops in the HVAC system. The refrigerant loop, which ran between these units and the huge condensers on the second floor roof, and the chilled water loop which ran between these units and the air handlers located in various parts of the building.

There is a bomb shelter in the basement. I found a couple of olive drab cans of civil defense water laying around. The lights were not working at the bottom of the stairs, so I chose not to go into the bomb shelter itself.

Stairs going down to the bomb shelter
Stairs going down to the bomb shelter

“Okay everybody, the missiles are on there way, so lets head down these stairs and pray”

There where two diesel generators, one was 325 KW which could run the entire building. The other was a 200 KW which could run the critical building functions. The fuel storage consisted of two 10,000 gallon tanks buried in the ground outside. Each steel fuel tank had a cathodic protection circuit. Basically a small negative electrical current was passed to the steel tank to keep it from rusting. Apparently it worked because when the tanks were removed in 2000 after 45 years in the ground, the primer was still on the outside of the tank.

Electrical switch gear, part of power company sub-station
Electrical switch gear, part of power company sub-station

The building has it’s own power substation. The electric from the utility company comes off the pole at 13,800 volts and goes to a large step down transformer on a pad outside. From there 480 volts is fed to this switch panel, where it is routed to motors loads or other step down transformers within the building.

Frame room floor, equipment removed
Frame room floor, equipment removed

On the main floor, there were rows and rows of wire terminal equipment, microwave transmitters, receivers and data and RF multiplexers in racks. The room in the above picture is about 10,000 square feet, there is another 6,000 square feet beyond the plastic heat barrier. This microwave gear received and transmitted data from Albany and Germantown to the north; Poughkeepsie, Putnam Valley, Ellenville, and Spring Valley to the south. All of that equipment is gone now, replaced by empty space.

Now the whole place is a little creepy.

There are about 500 copper wire pairs of telephone cable that came into various parts of the building to carry the DS-1 and DS-3 circuits that interfaced with the TELCO office in Kingston.

All in all, this was a serious building, no expense was spared in the construction and equipment outfitting.  The entire building is shielded with copper mesh screen embedded in the concrete walls.  There where redundant systems on top of redundant systems, something that you do not see these days, even in government buildings such as emergency operation centers (EOCs) and 911 call centers.