Tube suggestions for 811H

Discussion in 'Amateur Radio Amplifiers' started by AC2MM, Dec 30, 2018.

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  1. AC2MM

    AC2MM Premium Subscriber QRZ Page

    Jeff, thought you might be interested in this back story.
    What happened was this: During assembly at Ameritron, a washer was dropped inside.
    While I had it for 4 months, all was well.
    Then, I had to do some cable house keeping, and I moved the amp a little on the table, slid it over a bit.
    I turned on the amp, and a large flash appeared. Turned out to be that washer had landed next to that tube and arced.
    So Ameritron (MFJ) told me to send it back, because even though I had only one bad tube that I could see, the arc could have caused other damage.
    So they sent a FedEx call tag for free return shipping, and a new amp arrived at my door. Outstanding customer service by anyone's standards. 5 stars IMO.

    So I got the new amp going after reseating the tubes and reinstalling the Grid Protection Board I paid extra for . No problem.

    Everything was working great until it quit, no output. The head engineer got on the phone with me, and with the cover open and the switch bypassed (I know, I know...), he had me do a number of tests, mostly visual, but with and w/o my equipment also. It took about an hour to exhaust his suggestions based on the results.
    So they're sending another call tag, and this time I'm not removing the Grid Protection Board, so they can see it all.

    I have to say that the service was outstanding. Regardless of opinions on Ameritron/MFJ, poor customer service is definitely NOT a reason not to buy their products.
    And also, after listening to the work that RF Parts puts into the tubes to make sure you get a well-matched set of tubes, I decided to keep those as spares.

    People are really trying harder nowadays to keep the customer happy and do whatever they can to help. A little off topic, but I've received the same quality service from HRO and LDG Electronics. Off my soap box.

    So I'm 100W for awhile until someone figures out what's wrong with the last new one. My friend, a retired RF Harris Communications engineer, feels it's the output relay, but we won't know for sure until they look at it. Maybe I should have picked another amp, however. I don't have the bucks for a Palstar, which would have been my next choice.
    NQ1B likes this.
  2. N8FVJ

    N8FVJ Ham Member QRZ Page

    I have the three tube AL-811 and use three NOS Cetron 572B tubes. This amp uses the same strong power supply as the AL-811H and I can get 1KW PEP out with 100 watts drive. That would likely over heat 811A tubes. 1KW PEP out does not tax the power supply with an overly hot power transformer. I run it at 800 watts PEP out. The transceiver speech processor does draw a lot of average current vs no processor.

    This one time purchase of Cetron 572B tubes will last me the rest of my life and has much more reserve vs the 811A tubes.
  3. AC2MM

    AC2MM Premium Subscriber QRZ Page

    Hi Jeff,
    Well, I'll keep this in mind.
    Right now my main problem is keeping an 811H functioning properly.
    I've sent two new ones back, I'll let them sort this out.
    You obviously use more power than I do, I rarely exceed 300W because all I do is digital, so I really think I'm not stressing these tubes very much, and find no need to pay bigger bucks for more powerful ones.

    Thanks for your help,
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    Interesting the AL-811H has issues. I did not read about this anywhere.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    At the power levels you are talking about, 811As will be fine. The only real issue with that series of amps is when people push the limits without taking it easy on those tubes.
    Last edited: Jan 23, 2019
  6. N8FVJ

    N8FVJ Ham Member QRZ Page

    Reasonable AL-811/AL811H tube power handling output int0 close matched antenna.
    3x 811A for 500 watts PEP, 400 watts CW and 250 watts Digital. (Ameritron rates the AL-811 at 600 watts PEP and 500 watts CW)
    4x 811A for 650 watts PEP, 520 watts CW and 325 watts Digital. (Ameritron rates the AL-811H at 800 watts PEP and 600 watts CW)
    3x 572B for 1000 watts PEP out (800 watts PEP out assures no flat topping), 650 watts CW and 450 watts Digital
    4x 572B same output as 3x 572B due to amplifier HV power limitations.

    Note- my amplifier with three 572B will run with hot red plates at 600 watts carrier out. This suggests 125 plate dissipation CCS rated and the standard 572B 160 watts that is likely an ICAS rating.
  7. WD8T

    WD8T XML Subscriber QRZ Page

    I never experienced any increase in output power in an AL-811H running 3-572B tubes.
  8. N8FVJ

    N8FVJ Ham Member QRZ Page

    I went from about 700 watts PEP out with 3x 811A and up to 1KW out with three 572B in an AL-811 amp. 700 PEP watts out is too high for 811A tubes while I prefer 800 watts out with the 572B. The tubes are older RCA 811A & new Cetron 572B. Perhaps Chinese 572B are harder to drive? I use a Yaesu peak reading watt meter.

    So, I do not know what is wrong with your AL-811H or if you used soft 572B tubes.
  9. WD8T

    WD8T XML Subscriber QRZ Page

    No, I don't have soft tubes. Except for your claim of 1kw pep everything I've read about the substitution says there will be no increase in power due to the transformers limitations. I'm not saying you're not seeing that on your watt meter but I've never heard of anyone seeing a power increase over the 811A's.
  10. WT4W

    WT4W Ham Member QRZ Page

    Yep..... when the guy who designed the amp says that it's limited to around 800 Watts PEP by the transformer I tend to believe that.
    WD8T likes this.

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