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?

9 thoughts on “Longest tube life?”

  1. I’ve never had one come close to that, even with careful management and Sola transformers. I’ve heard of other BE FM’s in that same neighborhood though.
    Best I’ve seen personally is 8 years with a Harris HT20, and 7 years on a YU-148 in a QEI Box. The QEI never got more than 2 years on any replacements that followed.

  2. Paul,
    I remember a picture in Broadcast Engineering from around 1972 with several people from KMOX admiring a 5671 triode that lasted 100,000 hours. At that time we had a 5671 with 104,000 hours running in our Westinghouse 50-HG transmitter and it lasted over 111,000 hours when it was finally replaced. I always wished we could have come close to that with our 4CV100000C tubes in our VOA transmitters. We had too many filament cycles and never installed black heat.

  3. There was a story about a station back in te 80’s that had 12 years (and running) on a tube.
    It might have been Emac.
    *Is the tube running at full 20,000 output?
    *Has anything ever failed such as those pesky IPA transisters?

  4. David, you are right, the tube should never cool off. We try not to turn off this transmitter at all.
    Elliot, The TPO is 15.5 KW. Nothing in this transmitter has failed, not even the IPA.

  5. Never turn it off? I certainly understand the logic but how do you clean out the transmitter?

    And that brings the next question for the engineer masses: How do you practically establish and maintain clean transmitter environments? Down here in the deep south, the summer temps get in the 100’s and if your A/C dies you have no choice but to introduce outside air (which is filthy).

  6. Alan, it’s more of a figurative never than a literal one. As far as clean transmitter sites; this site is air conditioned, and the building is pretty well sealed up. Thus the cooling a closed loop, which keeps a lot of the dirt, bugs, mice, and other crap out. The emergency cooling fan has a filter on the intake louver, which also helps.

    Last time I looked inside this transmitter, it was pretty clean.

  7. You won’t get that out of the next tube. Tube life has been steadily decreasing on even new tubes for the past several years. In transmitters that are in otherwise good condition, tubes that once got 2-3 years now do well to make 100% at 1 year. This seems to be across the board.



  8. The BE “T” series transmitters seem to get better than average tube life. I am on the 6th year on a 35T running 33kW TPO, and another 35T at 6.5 years running 24.5kW. Mine only go off for quick cleaning and a visual inspection. Other then that they are on. Neither of these boxes has sat down on the job.

    As far as keeping it clean; a closed system is the way to go. I operate my sites with dual stage split systems,X2. So I have to have both systems fail to consider going to the aux site. The systems are fed from different services, so a failure on one power source will hopefully not touch the other one.

    I put these 35Ts on the air in 2005, and they are both clean and shiny inside. The HV cables attract a fine dust, but thats it, and that dust is easily removed. I just retired one to Aux status—replaced with a GatesAir FAX-40K. The other 35T will be retired next year replacing it with another FAX-40K

  9. Hi Chaps,

    In the 1970’s I worked at the BBC LF/MF station at Droitwich England. One of the jobs at the weekend for the young Technical Assistant on shift was to annotate the filament hours. The two long wave 2ookW transmitters were Marconi units from WW2 that had originally been installed at the LF site at Ottringham on the East Coast of England for broadcasting to Nazi Germany. There they were combined to give 800 kW on test and 600 kW normally. The tubes were by Marconi Osram and at Droitwich the CAT30 modulators in Class B were up to 220,000 hours on the fil clock, the CAT27s in the push pull generally lasted 150.000 hours. So you may have a way to go with the 4CX tubes over there. Keep up the good work on the site.
    Dave G4OYX ex VoA/BBC Woofferton UK now retired.

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