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Advice with an 811H amp

Discussion in 'Amateur Radio Amplifiers' started by K1OIK, Dec 29, 2017.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It was an open 50K resistor.

    Which is what I posted it would be back at the beginning of the thread.

    Burt said he measured them all, and they were all 50K. Evidently, that wasn't quite correct.

    Explains the long bleed-down time and everything else.
    WB1E, N0TZU and W1BR like this.
  2. AB8MA

    AB8MA Premium Subscriber QRZ Page

    Wow. Thanks, Steve.
  3. WG8Z

    WG8Z Ham Member QRZ Page

    Imagine that !
    There are two kinds of bleeders in those amps.
    Those that have failed.
    Those that will fail.
    N0TZU likes this.
  4. W1BR

    W1BR Premium Subscriber QRZ Page

    In short,he finally realized that the advice given from page one was correct, and that he probably had to remove a lead on each resistor to reliably measure each one. Note that the mystery solution only happened immediately after I posted general advice on how to measure those resistors. Whatever.

    A Google search of the scorched earth left by a certain caped crusader is ample testimony as to who is real bully.
    Last edited: Jan 7, 2018
    WB1E likes this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Mystery solved by WB2WIK in a few τ.
    W1BR likes this.
  6. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    That advice was of no help whatever but you did say this:
    "There was a known problem with damaged bleeder resistors used in a run of those amps.
    Classic symptom of an open equalizing/bleeder 50k resistor is internal arcing in the cap it parallels.
    In short, a clicking noise...."

    That combined with WB2WIK was very helpful. I had measured all the resistors while in circuit, which was a mistake leading me to believe they were all 50K. What I don't understand is they were all warm, how could an open resistor be warm unless it was arcing inside and the source of the click.
    Insult me all you want I will offer no retort to you because the italicized comments were quite helpful. I give credit where it is due.
    Is Ameritron the K-Mart of amplifiers (the junk goes in before the name goes on?)
  7. W1BR

    W1BR Premium Subscriber QRZ Page

    This wasn't helpful? You had it fixed with no further requests after it was posted? My feelings are hurt.

    1. [​IMG]
      K1ZJHHam MemberQRZ Page
      For any 811 series Ameritron owners following this thread... if you are concerned about the 50K resistors, you can check them with an ohmmeter. First, ensure all caps are fully discharged and the amp is unplugged!

      You will need to unsolder one lead at a time to do a resistance check for each device. You cannot measure the resistor across a large value electrolytic without introducing errors as the capacitor charges. A leaky cap will also affect the reading.


      K1ZJH, Yesterday at 10:43 AMReport
  8. AF7XT

    AF7XT Ham Member QRZ Page

    I stayed out of it because I have a personal fault of some magnitude. I like Burt. We have conversed infrequently but pleasantly over the last two years. Burt just isn't like everyone else.
    Maybe that's it .

    Way back somewhere in the first few pages I saw "audible snap" and "200 volt HV drop" . I knew immediately what it might be and exactly where to look.

    You see, most of what I Have been able to acquire for myself in the way of amateur radio gear has been used up, abused and neglected for want of diagnosis and a bit (sic) of effort. some examples are...

    a Tempo 2020, SPROCKETS.htm
    and a 15pf disc ceramic (c157 in the neut line)

    a TS-830S , HV cap and diode, tube short with screen and cathode resistors, transistor in the voice processor, carrier oscillators in left field, dead "fix" button, L41 (rewound) and bandswitch disassembly repair and re-assembly (a real chore) .

    a FT-857D, requiring micro surgery to repair the area around the "MARS mod" and a failed attempt to install a IF tap. Actually rebuilt sections of board and trace.

    a NCL-2000 that looked like a bomb went off in it .

    a HA-10 that had been mono banded by 11m monkeys, There really isn't much Heath in it anymore.

    Name a hideous 11m tube amp and I've been there. Some had no plate voltage metering past "smells like chicken". Others had nothing in the way of bleeder resistors other than an after thought.
    A Heath IM-11 probably saved my life on many occasions.

    So back on one topic or another ...

    It is often neglected when discussing the 811 tube in any of its many incarnations, what circuit support structure?
    30L-1 and the disastrous neutralization scheme ?
    Various "ungrounded grid" issues?
    HV power supply issues. HV high, low, unregulated, bleeder or choke.
    Cooling not only of the tube envelope but the socket and pins.
    The tank circuit being so abrupt that reduction drives are necessary.
    Not cut off, resting or in stby.

    Then add the clueless user. Through ignorance or lack of understanding many 811's have failed simply in tuning. Attempts to squeeze every last watt out of an amp on the way to advertised output will end predictably.

    When I read it was an open bleeder I didn't gloat or begin a tirade I just remembered an 8950 monster that had the same issue and smiled because I knew that time so long ago wasn't wasted. I had learned something then that applied today.

    Maybe because I don't expect much from the 811 I'm not disappointed. Maybe because I'm a realist I don't believe everything I read and only some of what I hear. Could be I'm a bit jaded and don't expect miracles from a near 70 year old tube design. (yes, 70 look up the 812). In this instance I chuckle a bit when (new) old school ops come unhinged at the mention of any beam power pentode, originally used as a horizontal deflection amplifier for television, used in an amateur amplifier. "That's a CB tube", "sweep tubes are the death of the ham bands" "splatter boxes" . All this about a tube design 25 years newer than the 812 that is capable of reasonable IMD figures ( no not great by any means). Hams are a curious breed .

    To Burt and whomever cares to listen. bleeder indeed
    K1OIK likes this.
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    K-marts around here all closed.:)

    Ameritron actually makes some pretty good amps. The AL-80B is a clear winner, and the "big box" amps (AL-82, AL-1200, AL-1500) just work and work and work and work and run legal limit power.

    The AL-811/811H are extremely popular because of their low cost, small size, light weight; but nobody pretends they're "good" amplifiers. They're adequate but marginal designs. If you don't mind doing repairs now and then, they can last a long time.

    I wouldn't use one on AM except at quite low carrier power levels (maybe 75W carrier, which is ~300W PEP). Above that, stand back.:p
    WA7PRC and K1OIK like this.
  10. KB4MNG

    KB4MNG Ham Member QRZ Page

    If you get help from some one, they need to be thanked and you need to feel thankful. I have received numerous help advise from many on the board. I'm very thankful for their time and experience with attempting to assist me with a problem.

    I thought it was common knowledge a component has to be removed from circuit so it can be accurately tested. I'm no where near a technician on this stuff....

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