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

    So what's the advantage of the 572B tubes?
  2. K9STH

    K9STH Ham Member QRZ Page


    MUCH higher plate dissipation than the 811A tubes for one. The 572B tubes are much more forgiving of long tune up times and are capable of running considerably more power than the 811A tubes. Using them should result in several times the lifespan of the tubes when compared with the 811A tubes.

    Now, with the AL-811H amplifier, you will not really be able to get that much more power output because the power supply is not up to the requirements for higher power. However, getting the much overrated power output of 800-watts (as proposed by Ameritron) might be achievable and certainly running that kind of power would not hurt 4 of the 572B tubes.

    Glen, K9STH
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Two advantages:

    1. You can prolong tune-up times to "forever" without hurting the tubes; eventually you may melt down the power transformer, but the tubes won't care.

    2. You can run as much power with two 572Bs as with four 811As, so you don't necessarily need four of them; although input and output matching will change a bit.
  4. AC2MM

    AC2MM Premium Subscriber QRZ Page

    To be honest, the extra money for those tubes aren't justified for me.
    I work only digital and never exceed 300W. I have had it to 350W but 300W is convenient with my Palstar Wattmeter 300W/2000W. Ameritron also told me to never go beyond 400W when using Digital.
    I bought the set of 4 matched tubes from RFParts as you guys suggested, plus one extra.
    The extra one is going in first to make sure nothing else was affected by that arc caused by the lockwasher left in the bottom of the chassis.
    If it works fine, I'll let it cool down and install the matched set.
    300W seems to work extremely well to get my signal around the world with my SteppIR.

    Thank you all for taking the time for your suggestions and advice,
  5. W1QJ

    W1QJ Ham Member QRZ Page

    We accept bargain and extend favorable cooperation with friends worldwide.

    The above is a statement made in the link above. Can someone translate this into English for me. I think it means that they except less money if you want to make a deal???
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think bar gain is how loud you get when you're in a bar.
  7. G3YRO

    G3YRO Ham Member QRZ Page

    I've always bought Chinese Valves direct from China . . . usually a fraction of the cost of getting re-branded ones from the USA ! (and never had a faulty one)

    Roger G3YRO
  8. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    Remember, a rebranded tube is the least expensive tube a manufacturer has to offer and they save the best stock for their own branding. so if you pay a premium for a name brand that is sold by a company that does not manufacture tubes, chances are, the tubes are not the highest quality the tube manufacturer hasd to offer!

    Even tho you buy a new high quality tube from a manufacturer, the quality of materials may not be as good as they used to be. Altho, there are specialty tube manufacturers that specialize in high quality products, and will build a tube to specifications beyond original. But it costs big bucks...

    I have been toying with the idea of having a special run of 572Bs made for grounded grid RF amps, but the amps would have to be modified to use them, otherwise it would be a waste of money to use them. Or the other idea would be to make an amp with the special tube and see if people would buy it. The problem is, solid state amps and old tube amps would probably be less expensive...
  9. AC2MM

    AC2MM Premium Subscriber QRZ Page

    I had a talk with a guy at RF Parts, and he convinced me that his people do everything they can to properly match tubes correctly for a complete set, and I believe him.
    As it turns out, Ameritron shipped me a new 811H, all checked out by their engineer himself. (Rob)
    But instead of returning the full set of new tubes to RF Parts, based on our conversation, I kept them all nicely wrapped up for that time down the road when I need a new set.
    By then, if I don't abuse the new one, the cost will probably have gone up 25% or so.
    Robb did not recommend putting in a set of 872B's, in his opinion, it doesn't justify the cost. I don't run this unit over 400W anyhow, mostly 300W on Digital modes only, so a more powerful tube is wasted money to me. To each his own...

    Thanks guys,
  10. N8CMQ

    N8CMQ XML Subscriber QRZ Page


    It isn't so much the output power, but the amount of time the power is applied to the 811 vs the 572, especially when tuning up.
    And if I understand it properly, if the plate of an 811 shows color, it is done, while a 572 is just getting warmed up.
    So it is more of a safety reason to change from one to the other.

    But if you want to keep the 811 original, I can understand that as well, as I like certain pieces of equipment to be original vs a hacked piece like the amp I am modifying. Anyone inheriting my amp without the knowledge and prints will be tempted to toss it as it isn't anywhere near original.

    There may be mods required to put 572B tubes in your amp tho, and I would research that if you change your mind.

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