The Tectrol TC91S-1465 power supply

Also know by its Nautel Part number: UG-39

Nautel V-10 FM transmitter

These are the stock power supply for 3rd and 4th generation Nautel V series FM transmitters, which were produced in the 00’s decade starting around 2005 but were discontinued sometime around 2009. First and second generation V series transmitters used Nautel made power supplies.

Tectrol TC91S-1465, aka UG-39

The OEM PA power supplies were made by Tectrol and were designed to put out 2120 watts per unit. The V-10 transmitters have eight PA supplies, one IPA supply with an option for a hot standby IPA supply. Like all such things, occasionally they fail for various reasons.

Unfortunately for Nautel, Tectrol stopped making these supplies and no longer supports them. Nautel won’t fix them either, however, they will sell a $3,200.00 (per supply) retrofit for a new supply.

Tectrol TC91S-1465, cover off

We take care of seven of these transmitters and overall, they are fairly reliable. They are not terribly old either. However, spending $28,000.00 to replace the UG-39 power supplies seems… somewhat steep. One station uses four V-10 transmitters combined to make a 40 KW transmitter. For that station, it would cost $115,000.00 to replace all of the power supplies on a transmitter that is barely 13 years old. In this time of economic instability buying a new transmitter is not an option either.

Tectrol TC91S-1465

Necessity being the mother of invention; we had a few of these defective power supplies kicking around, I decided to destructively reverse engineer one and determine the failure mode or modes. Special thanks to COVID-19 for giving us lots of spare time to do things with. Pete the Bench Guy, made up a test jig with a connector and some test points. With this, he can provide 240 VAC into the unit, feed 0 to +5VDC to the control pin, thereby vary the output voltage, look for faults, get ready indicators which the transmitter uses, etc.

Thus far, we have about a 50% 80% 90% success rate with these things. The failure modes vary from blow MOSFETS in the H bridge, bad PDM chips in the controller, fried resistors, a few other unusual things, etc. After repair, they will burn in for 24 hours in a nearby V-10 transmitter before we send the repaired unit off to wherever it is supposed to go.


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 not 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:

A nice row of transmitters
A nice row of transmitters

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
Energy Onix ECO-6

Energy Onix ECO-6 tube type transmitter.  One of Bernie’s better designs, a grounded grid tube with 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.
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
Noticed this after some particularly strong thunderstorms

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

USS Slater radio room
USS Slater radio room

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: http://www.engineeringradio.us/blog/2014/12/longest-tube-life/

The last one was last fall: http://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 on line on June 6, 2001.  It lasted until May 28th, 2019 with almost no down time.  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.