Chinese 811A and 572B tubes possible cause of early failure

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Jul 18, 2019.

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  1. N8FVJ

    N8FVJ Ham Member QRZ Page

    Thoria is a slang word used in the tube manufacturing industry such as at the Towanda plant in PA that built filaments. It is actually called thorium. The post clearly states early failures (loss of emissions) of the Chinese 811A & 572B tubes. The tubes have to have thorium used in the filaments or they would not function correctly due to the low filament operating temperature as seen by the color (yellow-white). In other words non-thorium filaments at the low operating temperature would produce a weak (low emissions) new tube at best.
     
    Last edited: Jul 20, 2019
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Most tubes fail because of abuse.

    I baby mine.

    Tube abuse is as bad as child and animal abuse. :p

    Cats abuse amps and radios by setting on top of them, There is that too.
     
  3. N8FVJ

    N8FVJ Ham Member QRZ Page

    Almost all amps using 811A tubes are the Ameritron AL-811 & AL-811H now. Tube abuse is due to Ameritron states 600 watts out (AL-811) and 800 watts out (AL811H). They over-rate the amps for advertising purposes. The amps are 450 watts PEP (AL-811) and 600 watts PEP out (AL-811H) and those ratings are not conservative either. Output is less using CW and RTTY is even less output. Average PEP output is normally no more than 20% average power, but a speech processor can increase that as high as 50% average power. The tubes fail early due to the Hams using the Ameritron specified over-rated output.
     
    Last edited: Jul 20, 2019
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    The Zed has hardly been swamped with reports of 811 failures/short life.

    -Abuse of tubes is the most likely failure cause. Certainly advertising exaggeration contributes to the problem. Similarly, the least expensive amplifiers tend to attract the least experienced operators.

    -As has been repeatedly mentioned here for at least a decade, RF Parts screens their tubes and rejects poor performers. One can surmise that rejected tubes end up in other vendors, or individual sellers online stores.

    You get what you pay for.
     
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The AL-811 should be run at 450-watts output on 160-meters through 20-meters, 400-watts output on 17-meters and 15-meters, and no more that 350-watts to 375-watts on 12-meters and 10-meters. The AL-811H should be run at 600-watts on 160-meters through 20-meters, 500-watts on 17-meters and 15-meters, and 450-watts on 12-meters and 10-meters. That is, when the final amplifier tubes are 811A. With 572B tubes, the AL-811 can run 800-watts output from 160-meters through 20-meters, 700-watts of 17-meters and 15-meters, and about 600-watts on 12-meters and 10-meters. With 572B tubes the AL-811H can run 800-watts on all bands but the power supply is going to take a beating especially on 17-meters and the higher bands.

    Ameritron / mfj severely overrate the AL-811- series to sell more of the amplifiers. You can get the higher power out of the amplifier but the tubes are going to suffer.

    Glen, K9STH
     
    KQ0J, N2IIE and KM1H like this.
  6. N8FVJ

    N8FVJ Ham Member QRZ Page

    You are exactly right Glen.
     
  7. KM1H

    KM1H Ham Member QRZ Page

    Wrong again, it is an accepted engineering term used by engineers and others in the industry.

    I have yet to see ANY proof that the current Chinese 811A and 572B have reduced thorium. Please supply qualified papers on the subject not just some WAG with nothing to back it up.
     
  8. N8FVJ

    N8FVJ Ham Member QRZ Page

    I did not ever state the tubes have reduced thorium content. I stated the filaments may not have the carbon film to reduce long term thorium loss.
     
  9. WN1MB

    WN1MB Ham Member QRZ Page

    And a goodly amount of absolute crap being foisted into the marketplace by our Chinese friends in trade.
     
    WQ4G likes this.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You could joing PETA, People for the Ethical Treatment of Amplifiers.
     
    WA9SVD and KA9JLM like this.

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