This is a Hughey Phillips mechanical tower light flasher that has been in service since 1960. Basically it is a motor connected to a cam that rocks a mercury relay back and forth. These were standard technology for tower lights from the 1930’s through about 1970 or a little later. They were very reliable, we still have some with a “pancake motor” in use on some of our towers. They were very robust and immune to lightning damage, RF interference and other problems. The only maintenance that I can think of is lubricating the motor bearings. Eventually, however, they do wear out. Cold weather seems to take its toll, often causing the motor to stop.
This particular unit is mounted inside the tuning house for the far tower (north tower) at the WGHQ antenna array. It has finally reached the end of it’s existence; the motor bearings are shot and it has gotten stuck in both the on and off position this year causing the FAA to be notified of the malfunction.
Today, I am replacing it with a solid state flasher (SSAC B-KON FS155-30RF). Solid state flasher units have been known to malfunction in high RF fields, such as AM towers. To cure that, the manufacture has built in 0.01 uf bypass capacitors, hence the “RF” suffix. Older units did not have the built in bypass caps, so external 0.1 uf bypass capacitors were normally installed on units mounted to AM towers. While I was working on this, I turned the transmitter down to 500 watts, no need getting any RF burns.
Naturally, this has to happen after there is two feet of snow on the ground. Also, it should be noted that this is the furthest tower away from the transmitter building. Now where did I put those snow shoes? Never mind, it has been very cold and the ground is frozen solid, I’ll take the truck… This is good because I will have all the tools, drills, nuts and bolts without having to walk back and forth several times in the snow.
I removed the motor and mercury filled relay. I’ll have to figure out how to dispose of the relay. I then drilled a mounting hole through the base of the old flasher housing and bolted the solid state relay to it. This is required because the solid state relay needs a pretty good heat sink.
Turn everything back on and: Ta-da! All works normally, tower beacon is flashing away up there. Time to leave.
Pull forward about 2 feet to turn around and CRUNCH! The truck goes through the ice of a hidden stream. Any attempt to move only makes it worse:
Put in a phone call to the one guy I know that can get me out. About an hour later he shows up with chains, a shovel and a come-a-long. We attach the come-a-long to the fence support post and pull the truck out backwards 1/2 inch at a time. It took us about an hour and a half to get it all the way out so I could drive it back across the field. I’d have taken some pictures, but my guy; he was a little grumpy.
I won’t do that again.
Still, I did the job I came to do, so it was a good day after all.
7 thoughts on “The mechanical tower light flasher”
Great post! Thanks. Too bad about the truck!
As always, you show the true side of real engineering. It ain’t just scribblin’ equations from a textbook, folks!
Neither the truck nor the author are none the worse for wear.
Your beacon bulb life should go up approximately 40% from the zero-crossing turn on cycling of the triac. Carefully break the mercury glass vile and save the mercury into a 35 mm film container, as it is worth some money to recyclers.
I recently reported a tower beacon “on but not flashing” to the FAA. After checking with a supervisor, the agent told me that he had no such notam and would just have to report the beacon out. This would seem to be a common failure. Has anyone else encountered this?
With tower lights, it’s an either or situation: it is either working or not. They are not going to put a description of the malfunction in the NOTAM, to them, it is out of order. Once the NOTAM is issued, you have 15 days to fix it.
Question: Where can I get one of these? I really could use one!!! Thank you!!!!!!!!!!!!!!!!!!!!!