WCKY transmitter site tour

This is of interest because of the GE BT-25-A transmitter footage.  I do not know the serial number of the WCKY BT-25-A transmitter, but it is looks identical to the old WPTR BT-25-A unit which can be seen in this post.  As I stated in that missive, I have not heard any transmitter before or since, that sounded as good as this unit.  They were really engineering marvels, even in 1999 when this video was shot.

No doubt the MW-50 (no letter) and particularly the DX-50 transmitters are more efficient. In this day and age when many AM stations are just scraping by, over paying for utilities is not an option. I noticed the Harris MW-50 transmitter with the PDM drawer open. That brings back memories too, those PDM boards where a pain in the rear, as I recall.

Donating old equipment

There is a propensity among radio engineers to save old equipment. Sometimes I look at something and think, “Man, that cost a lot of money ten or twenty years ago.”  Truth be told, much of what is saved will never be used again.  This equipment should be scraped or donated to someone who might find it useful.  One thing that is most appreciated by Amateur Radio (AKA Ham) operators are old 1 KW tube type AM transmitters.  Ham operators love these things, and with good reason.

A fair amount of repair work, some cleaning and a bit of reworking will turn what might have been a useless dust collector into a 160 or 80 meter AM rig and with a good story to boot.

Personally, I’d rather see a Gates BC1T or RCA BTA1R off to a new home than off to the scrap yard.  To that end, today we unloaded the BC1T at WLNA to a willing ham.  This particular transmitter had last run in 2001 or so and was used as a spare parts supply for other BC1T transmitters owned by the same company.  There was no way it would ever work again and truth be told, it really wasn’t needed any longer anyway.  Since the Harris MW5B was replaced as the main transmitter by a BE AM6A, the backup transmitter was never used.

Gates BC1T transmitter
Gates BC1T transmitter

John Aegerter, a frequent commenter on this blog, drove all the way from Madison, Wisconsin to pick it up.  Prior to pick up, I removed all of the tubes, transformers, crystals and glass envelope time delay relays.  I packed up the glass objects in a box.

Gates BC1T tubes, transformers and spares
Gates BC1T tubes, transformers and spares

There were several spare tubes and parts which are no longer needed.  These went with the rig, along with what ever manuals I could find.

Gates BC1T loaded into pickup truck
Gates BC1T loaded into pickup truck

The transmitter was then loaded into the back of a Dodge Ram 2500 pickup truck and tarped for it’s trip back to Wisconsin.

The burned contactor fingers

This is a set of burned contactor fingers on a Harris HS-4P 30 amp RF contactor:

Harris HS-4P RF contactor
Harris HS-4P RF contactor with burned finger stock

The back story is this:

The contactor in question is at the base of Tower #3 of the WBNR (1260 KHz, Beacon, NY) antenna array.  This is the tallest of all the towers, at 405 feet.  As such, it gets struck by lightning often.  There was at least one occasion where one of the inductors in the ATU got “sucked in” due to the huge magnetic field of a high current strike.  It is not at all surprising to me to find other component issues in this ATU.  Because of the burned contacts, I’d suspect that the station was switching modes under power, but I didn’t see that happening today.

The problem manifested itself in very high SWR after changing over from day pattern to night pattern.  This did not occur every time, in fact, it only occurred once in a great while at first.  Then, over the last couple of months it began occurring more and more often.  Since the snow drifts are now down to a manageable six to eight inches, it was a good day to go out and do some exploring.

First of all, I put the station into night time mode just to confirm that there is still an issue.  The transmitter, a Broadcast Electronics AM1A showed very high SWR and carrier fold back.  Left it in night pattern, but turned it off and took a walk, not a drive, to Tower #4 which is all the way at the bottom of a hill, near the old City of Beacon landfill.  I figured that I would check that one first, then look at Tower #3 on the way back.  When I got to Tower #3, I found the issue right away.

Fortunately, I was able to salvage a set of contact and contactor bar from another relay in the same ATU that was not using them.

Burned RF contactor bar
Burned RF contactor bar

The night pattern is only 400 watts, but these are tall towers, 225 degrees, therefore current and voltage are high at the base.  In fact, the slightest change at the base of the night time towers will greatly upset things.

Burned RF contactor fingers
Burned RF contactor fingers
Harris HS-4P contactor repaired
Harris HS-4P contactor repaired

This is the repaired contactor.  I will say, the EF Johnson RF contactors are easier to work on.  Those are the ones with the big rocker bar across the top and two solenoids on either side.  All of the wiring, status switches and contacts are exposed and easy to get to.  This one, not so much.  This is the BE AM1A transmitter

Broadcast Electronics AM1A transmitter
Broadcast Electronics AM1A transmitter

It is not a bad unit, compact, sounds good, reliable, etc.  In order to work on the power supply or anything in that top cabinet, the whole thing needs to be removed from the rack and taken down.  I suppose that is my only gripe about the thing.

Continental Shortwave Transmitters

I started my radio career working in HF radio, albeit somewhat different than broadcasting.   I enjoy the long distance aspect of HF communications and there is something about the high power shortwave (HF) rigs that interest me. This is a video of a Continental 418E HF transmitter. The carrier power is 100 KW capable of 100% modulation, when means peak output power is 400 KW. This particular model has a solid state modulator, which is in the cage where the guy is walking around. From the video, it would appear they had several blown fuses in the modulator section. The fuses protect the individual IGBTs in the modulator.

This is an older transmitter that is getting upgraded to a 418F. The heavy cable is the connection between the solid state modulator and the RF final section. Depending on modulations levels, it carries around 33 KV.

From the Continental Electronics website that details the SSM unit:

The modulator consists of 48 series connected modules which are switched on or off to provide the high voltage DC and the superimposed high level audio voltage. The switching is accomplished with Insulated Gate Bipolar Transistors (IGBT). A low pass filter follows the series connected modules which removes the switching signals and allows the DC and audio signals to pass to the RF amplifier. Because each of the modules is either in full conduction with very low loss, or turned off, again with very low loss, the overall modulator efficiency is in excess of 97%.

A full description of the SSM is on the Continental Electronics SSM website. It is an interesting read, including the description of the 12 phase transformer setup.

Finally, a video of the VOA transmitter site in Greenville, NC.

This is part 4 of 5, if one wanted to, one could click through to Youtube and watch the rest of them. The VOA stuff is, as the transmitter engineer notes, 1950’s technology. No solid state modulators in these rigs. Those are some old transmitters, still in service and likely to remain that way until the VOA closes that site down, some point in the future.

Like their FM counterparts, Continental HF transmitters are the gold standard when it comes to high power tube transmitters. Sadly, they no longer make transmitters for Standard Broadcast (AM MW).