Chinese 811A "Power Amplifier" Tube from Amazon ??

Discussion in 'Amateur Radio Amplifiers' started by K4ZOT, Dec 20, 2018.

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  1. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Copy that!
    The new tubes are all coming from the same place.
    Get that third tube going... switch two of them and see if it's the socket or the tube.

    edit: I just had a thought... be really careful to get the tubes in the correct orientation. It's not hard to stick one in wrong with those white ceramic sockets. Take a good look with a bright light and check the sockets for burned/discolored contacts too while you're in there.
     
    Last edited: Dec 21, 2018
  2. K4ZOT

    K4ZOT XML Subscriber QRZ Page

    I believe it is the socket, but will test it for sure. If it is the socket what components may be bad. I just need a little help on troubleshooting. There is no smell from the Amp or any visibly burnt parts.

    Thanks,

    Glenn
     
    Last edited: Dec 21, 2018
  3. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    No Filament light on one tube possibilities include an open filament, bad solder joint at the tube base, bad joint at the socket, burned or loose pin at the socket. A bright light and a good looksie (along with a VOM as needed) will help you find the problem.

    No bad smell from the amp is a plus. :p
     
  4. K4ZOT

    K4ZOT XML Subscriber QRZ Page

    Thanks - thats what I needed. Unfortunately the third tube socket is really hard to get to - its buried. But, I may get lucky and find it right away. I already found two loose tube sockets nuts that I had to tighten from the bottom of the case.

    Glenn
     
  5. N6UH

    N6UH Ham Member QRZ Page

    They're as low as $21 each and less than $70 for 3 shipped on the Amazon page I looked at. Got to be worth a try at that. Cheap as chips!
     
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Yeah, those amps are a pain to work on. If it is the socket and there was loose hardware, it would be worth taking some time and opening it up there to go over things. Loose connections or standoffs can get expensive.
     
  7. N2EY

    N2EY Premium Subscriber QRZ Page

    NQ1B, KA0HCP and N8VIL like this.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Check out the third tube -- might be a failure of the amp, or simply a failure in the tube.

    But re 811As, the reseller in question specializes in guitar and audio amps and although all modern 811As actually are made in China, they're not all the same.

    However, they may well look exactly the same.

    The difference between the "audio" tubes and the "RF amplifier" tubes isn't how they look, but how much voltage is applied to them by the circuit. Ham amps including the AL-811 actually provide higher B+ than the tubes are rated for, but audio amplifiers which are generally Class A do not.

    I've tested some 811As sold by "audio amplifier" tube specialists which would not survive well at the Ameritron B+ levels. Some might do just fine, I think it's probably a bit of a crap shoot.

    But if they provide a "return warranty" in case the tubes fail quickly, then not much risk other than the pain of taking all the screws out of the amplifier cover twice.:p
     
  9. AL7KC

    AL7KC XML Subscriber QRZ Page

    I bought some of the Chinese tubes, mistake. After years of good service from
    my originals, the new ones melted the plates within two weeks of swapping. Junk.
    Won't make that mistake again.
     
  10. K4ZOT

    K4ZOT XML Subscriber QRZ Page

    Well, I have had these Chinese tubes operating for over a week with heavy FT8 operation and so far so good. I'm getting 400 watts out with my AL-811.

    Glenn
    K4ZOT
     
    W1TRY likes this.

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