September 2018
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I almost hate to say anything, but

We have this certain transmitter which has been on the same tube since June 6, 2001.  Come to think of it, the transmitter itself has been on the air for the same amount of time without failure.  A testament to its designer…

Broadcast Electronics FM20T, WYJB, Albany, New York

Broadcast Electronics FM20T, WYJB, Albany, New York

According to my calculations, that is 151,691 hours or 17 years 3 months and 22 days.  The tube is the original EMIAC 4CX15000A that came with the transmitter.

I am a little nervous about turning it off to clean the cabinet.

EIMAC 4CX15000A tetrode

EIMAC 4CX15000A tetrode

We have a spare on the shelf for the eventual replacement of this tube, but I really want to see how long this thing will last.  This is also one of the last tube transmitters we have in main service.  There are several backup tube transmitters still around.

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13 comments to I almost hate to say anything, but

  • Scott

    You just screwed yourself. It will go down at 9pm on a holiday now.

  • David

    I like to think the designer already knew about the longevity of tubes in these transmitters by fitting the access cover to the cavity with screws, and not a hinged door with a latch 🙂

  • Paul, 15 years on the shelf is a long time with no intervention. Spare tubes should be hipotted annually. Tie all the filament and grid leads together and AC hipot at 70% peak plate voltage slowly ramping the AC until the barnacles are gone. Then DC hipot at 60% peak rating. Keep a record of the DC leakage current. This will help insure that a spare tube is not gassy when you need it at 9 pm on a holiday.

  • Gregg Richwine

    I assume by now, you’ve lost at least one controller power supply. If you haven’t, it will die when you perform your next cleaning shutdown. 😉

  • Elliot

    After 17 years service,you probably have nothing to gain beyond regular filter replacement.
    I would however strongly consider stocking some caps and such you should really change out when the day (or night) comes.

  • Bill Frahm

    It’s aliens. Just sayin’

  • Geoff PR

    “I would however strongly consider stocking some caps and such you should really change out when the day (or night) comes.”

    Wait – You mean critical failures can actually happen during the *daytime*?

    Not in my experience. 😉 It’s at inconvenient hours *only*…

  • Elliot

    Now now,let’s be kind!
    Many of us here are light sleepers and know the drill all too well.
    Let’s wish Paul a slow,successful sunset on this tube(and great weather) when it happens and a world record to boot:-)

  • Ed Butler

    Hi Paul I think you might want to check the BE manual for that 20T transmitter
    as I maintain the FM 20T transmitter here at WPLR and this 20T uses a 4CX12000A tube not a 15
    unless BE changed the design. great life on yours I get about 4.5 years at 17.5 TPO at WPLR.

  • Paul Thurst

    Ed, you are right. Now I have to go to the transmitter site and make sure that we have the right tube on the shelf.

  • Rich Redmond

    Paul, that is pretty amazing. Looks like the WYJB site. What do you use for a back up with the Gates FM (I think it was a 20H3 with a funky driver) gone?

  • Paul Thurst

    Rich, you are right, that is WYJB. That FM20-H3 has been removed. Currently, the backup is a PTEK 2500 watt broadband unit.

  • Barry McLellan

    Paul, I’ve had a similar experience with an FM-20T, we got over 14 years from the original tube, if I remember right. In that time, we even broke down the cabinets, and moved the transmitter from one rocky mountain-top to another. I wasn’t expecting much from the tube after that, but it lasted for another three years. And no trouble with the transmitter at all during that time. Since then, I remember only one more tube, that one at about 7 years now is getting soft. During the life of the transmitter I only remember having to change that low voltage power supply for the controller – that happened after we shut the transmitter off to change frequency – so have one of those on hand! But I whole-heartedly agree with you, this is one of the most reliable transmitters I’ve maintained, and low cost of maintenance as well.

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