3-1000Z Tube filiment Noise

Discussion in 'Amateur Radio Amplifiers' started by KE7TRP, May 20, 2015.

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  1. KE7TRP

    KE7TRP Ham Member QRZ Page

    I recently picked up an old BTI LK 2000 amplifier. It was in sad shape and not working. After fixing the Power supply, Band switch and timing, New RFC plate choke and door knobs and chimney, The amp is producing legal limit power on 10 to 80 meters. The PS is a traditional Supply with Center tapped UTC plate transformer at 3.5 KV with 25MFD 4KV oil can.

    The only issue is a high pitched rattle/noise that I thought was the blower motor bearing. I oiled and rubber mounted the blower only to find the noise still present. I carefully used a stethoscope and found the noise is from the tube itself. I disabled the filament power and instantly, the noise is gone.

    I pulled the tube and ran the amp and blower and there is no noise.

    I can tap the tube slightly and it does in fact rattle a bit. Not anything broken but it does have a chime to the filament.

    The tube runs full power and tunes up great.

    Has anyone had this kind of thing happen? Is this a fault of the tube or maybe my filament supply? I have tried everything to silence the noise with no luck. Its a very high pitched rattle that really gets into your ear and annoys the hell out of me. Is this a magnetic problem? I do not thing it is just vibration.
     
  2. REASTON

    REASTON QRZ Member

    I had 2 different 3-1000z amps in the 70's and none of them did what you describe. But the only way you are going to figure this one out is to get another (borrow) 3-1000z and try it. When I worked in broadcasting in the 60's, I used to hear all kinds of weird noises coming from transmitters but most of it was transformer noise or rattling from modulation. I can't ever remember hearing a filament rattle but I suppose it is possible since most filaments are powered by AC instead of DC current.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I don't have anything with a 3-1000Z, but I've heard filaments "sing" before. That can even happen with an ordinary tungsten filament light bulb. Usually happens just before they "die" and stop working.:p

    However, it would be good to get some advice from someone who actually has a 3-1000Z. They're pretty rare and haven't been manufactured in decades.
     
  4. KE7TRP

    KE7TRP Ham Member QRZ Page

    We where talking about this on the air last night on 80 meters and this morning I got a very informative email from an Eimac engineer. He explained that the 4-1000 and 3-1000 used a "pusher" style post that pushed open the Filament structure. They do make a chime if you tap on the glass at all when handling the tube

    The theory is that when the filament voltage is on, the structure expands and gets loose and then of course rattles.

    It sure is annoying. Its a high pitched rattle that sounds like a bad bearing in a blower. Its on all the time the amp is running in the shack. I had a brand new 4-1000A and sold it. I wish I kept it now. I will have to find another tube and swap it in.

    C
     
  5. W8JX

    W8JX Ham Member QRZ Page

    Have you run tube without blower? My thinking is maybe there is a vibration in fan that when filament is lite it resonants.
     
  6. KE7TRP

    KE7TRP Ham Member QRZ Page

    I can do that and I plan to. It was an odd problem because the noise is only there if the tube is lit.

    C
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page


    I have heard them sing for a week before they open, I just leave them Bee. It is a bit cool.

    I will have to put a stethoscope in with my Tube Tester now.

    Who would have thought they could be so handy.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I suspect it really is the tube filament.

    I have a 4-1000A amp and haven't heard this from it (yet) but maybe someday I will.
     
  9. W8JX

    W8JX Ham Member QRZ Page

    If it is filament you could try reducing voltage on it. It is spec'd plus or minus 5% from 7.5 volts. I would drop it to 7.1 or 7.2 volts and see if that cures it. If they do indeed sing when getting near EOL, reduced voltage would extend life.
     
  10. KE7TRP

    KE7TRP Ham Member QRZ Page

    I forgot to check fil voltage yesterday when I was working on the power supply. I can do that when I have some spare time. I have a very nice little variac for setting Filament current on a broadcast rig. I could mount it under the chassis and wire it up. Its run for 3 days and the noise is still there. I ran the amp at 4kV but the tank is a bit light and I hear some pops now and then. Does 1500 with 50 watts drive. I lowered the taps down and get about 3KV now. Cruises at 1000 watts out. Pushed to 1500. The amp does full power on 10,15,20 and 40. Slightly less on 80. I think its the small 80 meter add on coil. If the tube fails, I will just use a 4-1000 or maybe thought of converting it to the 3cx1200. There is plenty of room and its already been converted to forced air with a chimney. Would not be much work to get that tube going.

    I am also searching for a new plate transformer. This UTC S50 is maxed out. I would like to find a 220 volt primary, 2500 to 3500 volt range, center tapped transformer in the 800 to 1 amp range. If anyone has anything let me know.
     

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