FM transmitters – Page 5 – Engineering Radio

The BE STX 10

We just finished installing one of these units on Mount Beacon for WSPK. Mount Beacon is around 1,500 feet high and is accessed by a road that is a little bit rough. After the snow flies, the only way to get there is a snow machine or perhaps a helicopter. Thus, whatever is installed there needs to be reliable.

BE STX 10 mounted in Middle Atlantic Rack, WSPK, Mount Beacon, NY

My first comment, I recall 10 KW FM transmitters being much larger. This unit is pretty compact and we probably could have fit two of them in this Mid-Atlantic rack had we wanted to.

The transmitter itself is pretty simple, four RF modules powered by seven OEM switching power supplies with two fan power supplies, one for each fan unit. This is driven and controlled by an STXe 500-watt exciter.

The back has a 1 5/8 inch EIA flange output, some power connections, remote control interface, etc. Pretty simple overall.

I can also say, there was a noticeable improvement in the audio quality when this was placed in service.

Something is not right

The Goddamnitnotagain edition:

PA module with burned open output transformer

I went to do maintenance at one of our sites and noticed that a certain transmitter was running at half power. Followed the path of the fault log and found this. When I mentioned it to the station staff, they said, “Yeah, we noticed it sounded a little funny…”

This is the second time this has happened with this particular transmitter. In any case, this is what I get paid for, so I am certainly not complaining. If only every problem where this easy to find.

When I get back out there to replace this, I will bring out my network analyzer and sweep the antenna and transmission line to make sure there are no issues with that. In addition, I will double-check all the grounding to make sure the copper thieves have not made off with any critical components like the ground buss bar or #2 solid down lead wires.

A few pictures

Some things I have been working on lately:

Finishing up a transmitter site rehab. The BE FM20T is nearly 20 years old. The BE FM2C transmitters are new. There is also a rack of new fiber equipment and CODECs. This site has good utilization; there are three stations on one tower with a shared STL antenna and generator.

Energy Onix ECO-6 tube-type transmitter. One of Bernie’s better designs; a grounded grid tube with a solid-state driver section. This one needed some fans replaced and a new tube.

AM transmitter site. Looks like these vines have not been cut in a couple of years.

I wonder how much the guy tensions have changed…

Noticed this after some particularly strong thunderstorms

The reason why you do not use a POTS line phone during a thunderstorm.

I took a tour of the USS Slater, a museum ship in Albany, NY. The museum has painstakingly restored the ship to its WWII configuration. The main transmitter is the RCA TBL-8 seen in the left/center of this picture. This unit put out 200 to 400 watts CW or 150 watts AM phone. During the hostilities, it was turned off as allied ships observed radio silence unless they were sinking (and sometimes even then).

A little ChiFi tube type RIAA phone preamp. — A little ChiFi tube-type RIAA phone preamp.

I have been fooling around with this little 6AK5 preamp. I find it works very well and sounds better than the built-in phone preamp on my Kenwood VR-309. The FU-29 tube amp did not come with a phone preamp.

This is a short video clip of an audio processor at one of our transmitter sites. The fancy lights around the control knob are designed for the program director. They are saying “Buy me… Buy me…”

Almost Eighteen Years

I do not know what the record is for the longest tube life, however, this particular tube lasted 17 years, 11 months, and 23 days. That’s 157,596 hours.

I had written about this almost five years ago: https://www.engineeringradio.us/blog/2014/12/longest-tube-life/

The last one was last fall: https://www.engineeringradio.us/blog/2018/09/i-almost-hate-to-say-anything-but/

Eimac 4CX12000A power tube, serial number RHH108

This was installed new in a Broadcast Electronics FM20T transmitter which was placed online on June 6, 2001. It lasted until May 28th, 2019 with almost no downtime. Towards the end, the emissions started dropping off and we increased the filament voltage up to 10 volts. When you have to increase the filament voltage, that really is the end for a tube.

The new tube was put in and I carefully marked out the date in the maintenance log. The hour meter on the transmitter stopped working several years ago.

Prior to this, the longest tube life I’d experienced was an EEV 4CX35000C from an MW-50B transmitter RF section. When that tube came out, it looked like it have been on fire.