Ameritron AL-80B: How to tell if the tubes are good

Discussion in 'Amateur Radio Amplifiers' started by AD6OE, Jan 4, 2019.

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  1. AD6OE

    AD6OE Ham Member QRZ Page

    I am thinking about adding a used AL-80B to my station. Question is, how can I tell if the tubes are ok? There is one that I am interested in but the seller claims that he is getting 500 watts on SSB with 50 watts of drive. Seems a bit low to me but I don't have much experience with amps. Any thoughts? Is there a good test that I can perform when checking out used amps?
     
  2. KD0CAC

    KD0CAC Ham Member QRZ Page

    The best way to test power tubes - is in the amp they are for , so get a known good dummy load , or an antenna [ a tuner that can make the amps see 50 ohms ] that is 50 ohms on every band that the amp does , then see if it meets the output spec.s .
     
    KB4QAA likes this.
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    In an AL-80B, it's not "tubes," it's "tube." There's only one.

    500W output with 50W drive is a little bit on the low side, but actually not much. The tube has about 11 dB gain at 3000V, so if properly tuned and loaded (a big "if," since some people aren't very good at this:p) with 50W drive output should be about 600W.

    This also depends quite a lot on the user's AC line voltage and how much that might sag under key-down conditions. Running the amp on 240V is better than running it on 120V, mostly because the line voltage sag at 240V will be less, and that transfers to "higher key down voltage" from the high voltage power supply in the amp.
     
    N2EY, KD0CAC and KK5JY like this.
  4. WE6C

    WE6C Ham Member QRZ Page

    What meter was used to measure that 500w?
     
  5. AG5CK

    AG5CK Ham Member QRZ Page

    Out of curiosity I fired up my al80b. The tube is only a couple of years old and it hasn't been used much.

    On 20 meters with 50 watts input I get 620 watts out when tuned for max smoke. The measurement were made using an FM carrier, a dummy load, a bird 43 meter with a 100 and 1000 watt slug.

    110ma grid current. Right under 375ma plate current and 675 watts out on the built in watt meter.

    The amp is wired for 240vac. Resting plate voltage is just under 3kv and drops to 2750 under the test conditions.

    When the tube in mine went soft the input match changed. The radio was seeing over a 2:1 swr. Of course the output was lower than normal but since you haven't been operating the amp thats all irrelevant.
     
    KD0CAC likes this.
  6. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    What does than mean exactly? o_O

    Dave
    W7UUU
     
    K9ASE likes this.
  7. AG5CK

    AG5CK Ham Member QRZ Page

    I'll humor you. Turn the plate and load knobs until the amplifier produces maximum output.
     
  8. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    Electronics have been said to contain magic smoke.
    When a part fails the magic smoke escapes and the part quits working, but while it is failing you can tune it for maximum smoke!
    But before electronic tubes, they used kerosene heaters, and they could be tuned for max smoke if you turned the wick too high... XD
     
  9. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    Achieving maximum output and "things inside smoking" are not equal. I achieve maximum output in all of my rigs, yet no smoke happens.

    Why does your amplifier produce smoke at full rated power?

    That's the part I don't get. Why do you say "tuned for max smoke"? when you mean "maximum output" per the design of the device?

    There should be NO smoke. At ALL. Ever.

    Dave
    W7UUU
     
  10. KD0CAC

    KD0CAC Ham Member QRZ Page

    I'm working on getting a patent on a MAGIC SMOKE INJECTOR ;)
     
    K9ASE likes this.

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