Ameritron 811

Discussion in 'Amateur Radio Amplifiers' started by AJ4OG, May 13, 2011.

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  1. AJ4OG

    AJ4OG XML Subscriber QRZ Page

    I am looking at buying a used AL-811H. It is from a sk and the wife does not anything about ham. I don't know anything about the 811. When Its turned on in standby with the meter switch in the HV position it only goes to 800 to 850 volts on the meter. When I switch the to the IP position it the meter stays the same right around 800v or 300 ma plate current. The switch is flakey also. Any idea what could be wrong?
    Thanks Charles
  2. N6YG

    N6YG Ham Member QRZ Page

    How much is she asking for it and how is the amp wired 110 or 220?

    By the way those switches are easy to replace I just did all three on mine and it only cost about $2 a switch. the 811h is definitely an easy amp to work on much easier then my SB-1000.
    Last edited: May 13, 2011
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Which switch is flaky? The meter switch?
  4. AJ4OG

    AJ4OG XML Subscriber QRZ Page

    It is the meter switch. I have heard this is a common problem and I am not really worried about replacing it. The voltage seemed low though. I thought it was supposed to be 1700 or 18oo volts. She wants around $500.00 for the amp a MFJ-969 tuner, a Radio works Carolina Windom 80. There are a few other small things, not sure what works and what won't. Charles

    Just sitting here messing with the switch and now when I switch to ip the current goes to about 20 ma. Also a little more information all 4 tubes glow when it's turned on. One more bit of information the fan does not run either.
    Last edited: May 14, 2011
  5. N6YG

    N6YG Ham Member QRZ Page

    Once again how is the Amplifier wired ? is it wired for 220 or 110?
    If you don't know how to check here's a link to the manual the info on wiring is on page 4

    In that case you might want to take a closer look at the tubes and make sure they haven't been over heated which is a very common problem with AL-811's. Overheated tubes indicate abuse, but don't let then turn you off to the deal. A full set of new tubes is only about $90 or so from RF parts. Even if the tubes have been overheated they are probably still very usable. I've seen overheated tubes that easily put out 90+ percent of rated power. If the tubes have been over heated I would use that as a reason to negotiate a lower price.

    If you're not sure how to check the tubes here's a video that shows you how to basically inspect an 811a and it gives you an example of what an over heated 811a looks like. If you're not familiar with working around High Voltage and tube amplifiers then what ever you do don't just reach in there and grab a tube. You can easily inspect them with your hands in you're pocket and the tubes still in the sockets.
    Last edited: May 14, 2011
  6. AJ4OG

    AJ4OG XML Subscriber QRZ Page

    The tubes look good. My biggest concern is the HV. The 800 to 900 seems very low. Charles
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    How bright do the filaments in the tubes look? Are they nice and bright yellow, or dim?

    It "sounds" like your amp is wired for 240v and you're running it on 120v, which of course would explain the very low plate voltage.

    It should be impossible to plug a 240v amp into a 120v outlet unless somebody very ill informed used a 120v plug on 240v (bad idea, violates all sorts of codes, but it's possible).
  8. N6YG

    N6YG Ham Member QRZ Page

    That was my first thought as well. That's why I kept asking how the the amp was wired, Is it wired for 110 or 220? heck I even provided a link to the manual. still waiting for a response.

    Oh its very possible I've seen it first hand. I've been to ham shacks where the owner had rewired a 120 outlet to 220 using the same receptacle with nothing more then 220 written in sharpie on the outlet, very sketchy sh!t if you ask me.
  9. AJ4OG

    AJ4OG XML Subscriber QRZ Page

    Holy Cow! It was wired for 240v. It had a 120v 20 amp plug on it. It did have the correct 8 amp fuses in it though. Thanks for all the help.I sure I will have a million questions. Charles
  10. W8JI

    W8JI Ham Member QRZ Page

    The problem with the switch is the switch vendor moved offshore several years ago, and the contact materials are not as reliable for low currents. You probably can flood the switch with WD40 and make it work by flipping the switch a few dozen times. I'll try to find a better solution, but the hole in the panel only takes that type switch. The switches used be good, but then my refrigerators used to last 20 years too before they went off shore.

    The low voltage reading is a concern because the meter resistors and meter is VERY reliable. The multiplier resistors are 1 meg high reliability resistors.

    This is a bridge rectifier supply, and NOTHING can fail to make it half voltage without a lot of smoke. The power supply is very reliable, and a half-voltage failure is very unlikely. About the only thing that can make a real half-voltage situation is if the amp is wired for 240 and plugged into 120.

    73 Tom


    Woops, we posted at the same time. :)
    KH2ZZ likes this.
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