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Longest tube life?

We may be going for a record here; this Broadcast Electronics FM20T was placed in service on June 6, 2001:

Broadcast Electronics FM20T, WYJB, Albany, New York

Broadcast Electronics FM20T, WYJB, Albany, New York

The original 4CX15000A tube is still in use.  I wrote about this a few years ago in this post: Longevity.

I thought by now, we would have changed out that tube.  A few quick calculations shows that the tube has been in use for 118,289 hours or 4,929 days or 13 years 6 months and 3 days.  Anyway you look at it, that is a long time for one tube in nearly continuous use.  I noticed the hour meter is lagging a bit:

Broadcast Electronics FM20T hour meter, WYJB, Albany, New York

Broadcast Electronics FM20T hour meter, WYJB, Albany, New York

Reads 113051.24, which is 5,238 hours different than what I calculated from the maintenance log.  I noticed a slight discrepancy in hours two years ago and attributed it to various off air periods.  However, between then and now, this transmitter has not been off at all.  Thus, the hour meter is wearing out before the tube.  I would say that this is because of excellent filament voltage management,  but I think we simply have a really good tube.

Has anyone else had a tube that lasted this long or longer?

Transmitter Haiku

I wrote a little Haiku about Thanksgiving dinner:

Telephone rings
Old transmitter beckons
Dishes get cold

Not exactly the 5/7/5 of a traditional haiku, but close enough.  This year, it was the nearly 30 year old Broadcast Electronics FM35A at WEBE.   A set of readings from the remote control reveal; zero forward power, zero plate current and 12.8 KV plate voltage.  My first assumption was some sort of drive issue; a failed exciter or IPA driver.  After starting the backup transmitter and making sure that it was running stably, I spoke with the program director and told him we would be out next morning.

Upon arriving at the transmitter site, I found the BE transmitter had no filament voltage.  An obvious clue, I began working backwards from the tube socket until I found this:

Broadcast Electronics FM35A filament voltage regulating transformer

Broadcast Electronics FM35A filament voltage regulating transformer

This is the auto-transformer that regulates the filament voltage.  Schematically, it is noted as T204 and it is in series with one side of the filament transformer.  This one is burned open.  The bad news;  Broadcast Electronics does not stock this part, it is a special order item, the replacement part costs $2,800 dollars and it will take a few weeks to get here.  The good news, after digging through our stock of old transmitter parts, I found an exact replacement:

Replacement part, T204, BE FM35A

Replacement part, T204, BE FM35A

Replacement part name plate, T204, BE FM35A

Replacement part name plate, T204, BE FM35A

We will be installing it on Monday morning.

Repairing the Nautel VS2.5 transmitter

The newish Nautel VS2.5 transmitter installed at WJJR had an RF module failure. This particular model transmitter does not have slide in RF modules as other Nautel transmitters do.  To fix this transmitter, it has to be pulled out of the rack, flipped over and opened from the bottom. The module replacement is very straight forward, there are five solder pads that connect to wires carrying the input, output, power supply and bias voltages.

Nautel VS2.5 transmitter RF modules and combiner

Nautel VS2.5 transmitter RF modules and combiner

The troubleshooting guide gives good instructions on how to check the PA MOSFETS with a DVM. I found that 1/2 of the device in PA1 was bad:

Schematic Diagram, NAPA31

Schematic Diagram, NAPA31

All in all, not a very hard repair. This was under warranty, so a replacement RF pallet was sent to the station without charge. The problem is more about where the transmitter is located:

Killington Mountain, Killington, VT

Killington Mountain, Killington, VT

Killington Peak is the second tallest mountain in Vermont, topping out at 4,235 feet (1,291 meters). In the winter, one can take the chair lift to the top. In the summer, the road is drivable with a four wheel drive. In those in between months, access to the top can be very tricky at best. We had a pretty wet spring this year, so the roads up the mountain are just now becoming passable for vehicles.

Even after reaching the parking lot, there is still a 10 minute walk to the peak, another 200 or so feet up a steep, rocky trail.

Further complicating things, this transmitter is wedged into this little shack, which holds; a BE FM3.5A transmitter (defunct WJJR), a Harris HT3 transmitter (WZRT), an ERI combiner, two racks of equipment (STL’s, Exciters, remote controls, etc) a backup QEI transmitter, an Onan generator transfer switch:

Killington Peak fire tower, WJJR WZRT transmitter building

Killington Peak fire tower, WJJR WZRT transmitter building

Both stations run into this ERI half wave spaced antenna:

WJJR WZRT ERI antenna

WJJR WZRT ERI antenna

It is very tight in this transmitter room. There is a new tower on Killington Peak, which is still under construction. At some point, the plan is to move into the larger building next to the new tower.

Killington Peak tower

Killington Peak tower

On a clear day, the view from the top is spectacular. On this day, the peak was in the clouds, so not so much:

Killington Peak view

Killington Peak view

It is a great site, the HAAT is 2590 feet (790 meters) and the stations carry forever on relatively low power outputs.

Failed High Voltage Contactor

This contactor was used to replaced the Furnas contactor installed as original equipment when the transmitter was manufactured in 1986.  Furnas is no longer in business, thus the ABB A145-30 was substituted. It purchased from directly from Broadcast Electronics for an FM35A transmitter:

ABB A145-30 contactor

ABB A145-30 contactor

It was installed about 18 months ago and has been in nearly continuous use since.  The broken white plastic housing surrounds the contactor coil and is responsible for pushing and holding down the contact fingers.

ABB A145-30 contactor coil cover

ABB A145-30 contactor coil cover

Looks like the coil is running too hot and damaging the plastic. This resulted in a failure of the contactor to make and no high voltage to the transmitter PA.  Obviously a problem.  I spoke to BE about this and they did not have a good answer.  Actually, what they said was “That contactor is rated for 220 amps,” which is true enough. The only thing that I can think of is the coil is rated for 208 volts and the transmitter is connected to a 240 volt delta service.

A new contactor was ordered and installed yesterday.

I will investigate the coil voltages further, but for now, the 27 year old transmitter remains on the air.

Broadcast Electronics FM35A

Broadcast Electronics FM35A

Exploding Parts

We or rather, I have been working on installing this CCA transmitter as a backup unit at one of our sites. It was installed as a backup at another site, but was mothballed about ten years ago. Now, we need to get it running again and re-tune it. Seems like a fairly uncomplicated job.

CCA FM-5000DS transmitter, circa 1971

CCA FM-5000DS transmitter, circa 1971

Except, every time I start it, another one of these 1000 pf bypass/feed through capacitors fails. They are located at various points around the PA enclosure and route AC voltages into and out of that enclosure.  The bypass function is needed to keep stray RF off of the control circuits. Normally, they have been failing with a medium resistance fault (40-70 ohms) to case.  That causes the control circuit breaker to trip.

This time, however, it was on the primary for the filament transformer on the IPA tube.  Just a wee little pop, followed by some ozone smell and sans power output.  I have, thus far replace four of these and there are seven original still in the transmitter.

Feedthru capacitors

Feedthru capacitors

It is time to replace them all, otherwise this rig will fail when we need it the most.  Replacement part is a Mouser 800-24437X5S0102MLF, 1000 pf 500 v made by Tusonix Electronics.

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

Free counters!