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Ameritron 811H no grid current

Discussion in 'General Technical Questions and Answers' started by NZ4L, Nov 19, 2009.

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  1. NZ4L

    NZ4L Ham Member QRZ Page

    I just received a brand new AL 811H. I removed it from the box and opened the amp a removed the packing material, installed the 12 amp fuses, made sure the tubes were seated, replaced the cover, hooked it up and turned it on, the plate voltage is 1800 volts but when I tried to tune the amp "by manual instructions"the grid current meter remains zero. No power output at all. Need help. Thanks
  2. K9STH

    K9STH Ham Member QRZ Page

    Are you "keying" the amplifier? It sounds like the amplifier is still in the "standby" condition. You have to apply a ground to the "keying" jack on the rear of the amplifier.

    Glen, K9STH
  3. KB5WX

    KB5WX Ham Member QRZ Page

    You don't give much to go on . Let's start with the obvious . Do you have a footswitch or keying cable hooked up to the amp ? If so , can you hear the relay inside the amp when it is " keyed " ? The AL-811 does not have a rf detection circuit , so you have to either use a cable between the rig and the amp or use a footswitch to " key " the amp . You can use any type of momentary switch , but most ( myself included ) prefer a footswitch . If that's not the cure then we may need some more info . Also make sure the amp is in operate and not standby . Hope this helps . The 811h is a really nice amp for the money .
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Tubes being seated is nice. Did you also attach the four plate caps on the tubes?

    Is the amplifier "keying" (XMIT LED turns red when you do...with or without any drive)?
  5. K6CLS

    K6CLS Ham Member QRZ Page

    you didn't say so I have to ask - is your xcvr in CW or FM mode? in other words, is it actually driving RF in to the amp? if it's in SSB or AM mode, try yelling in to the mike and see if the grid current needle moves.
  6. NZ4L

    NZ4L Ham Member QRZ Page

    No I don't have a footswitch, I have the relay and alc cables from the 746 Pro connected to the amp. When I try to tune the amp up in the CW mode the operating light comes on and I can hear the relay keying but there's no output. The plate voltage is 1800 and when the switch is put in the Ip position the meter falls to zero as the manual says it's suppose to. The standby/operate switch is in the operate position. When the xcvr is keyed the plate current meter moves up a little but the grid current meter doesn't move no matter what the radio output. The coax is connected between the xcvr and the amp out to a inverted L vertical 1.8 swr. As far as I know I have done all the manual says to tune the amp but it still doesn't work. All four of the tubes seem to be seated good and the caps are all on good and they all light up. Hope this is a better description of the problem. Thanks.
  7. N4CR

    N4CR XML Subscriber QRZ Page

    Actually, it does sound like you are doing all the right things. If you can test the output wattage of your driving radio and it's anywhere above 0, then it's time to return it to the place of purchase and have a little chat with them about an exchange.
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What MODE are you using to do this?
  9. W0UZR

    W0UZR Ham Member QRZ Page

    Is your coax jumper from the radio to the amp on backwards? Jumper has to be connected to the RF IN on the amp?

    Is your radio connected to the "RF IN" on the amp, and the antenna connected to the "RF OUT" ??

    If you hooked it up wrong, don't feel bad. I have connected amps and antenna tuners wrong several times before. And when the amp is connected wrong, It don't work at all.....
    Last edited: Nov 20, 2009
  10. K4LSX

    K4LSX Premium Subscriber QRZ Page

    kit form?

    I also have the AL-811H and am quite happy with it. As another post said "it is a great buy".

    However, the QC at MFJ just plain stinks in many cases.

    The first AL-811 I bought had been dropped hard (pre-packing, box and packing perfect condition, so obviously at the factory) such that one rear corner of the chassis and cabinet was deformed badly...right back to the radio store it went. I have had other MFJ products with joints that had never had solder applied, cold solder joints, etc. In some cases it is like building a kit.

    I think it sounds like you have given it a 'fair shot'. You might try one last thing.

    !. be sure that it is "deader than a hammer" electrically.
    2. take the cover sure it is dead, again.
    3. give it a thorough 'exam' - mechanically and electrically.

    if no findings, take it back...won't be the first piece of MFJ they got back.

    don't give up on it - they are good property.

  11. W0UZR

    W0UZR Ham Member QRZ Page

    If you open that thing and look for cold soldering joints and ones that MFJ missed,,,


    That's to make sure that you don't turn up medium well or well done when getting electrocuited. And even then, KEEP ONE HAND IN YOUR POCKET AT ALL TIMES!!
  12. W0UZR

    W0UZR Ham Member QRZ Page

    Well? Did you get it working?
  13. K0CRX

    K0CRX Ham Member QRZ Page

    I can't help but wonder why you are doing this experimentation into a radiating antenna and not a dummy load.
  14. K9STH

    K9STH Ham Member QRZ Page


    Unfortunately, many amateur radio operators do not have a dummy load capable of handling the power output of a higher powered linear amplifier. In fact, many operators don't have a dummy load that can even handle 100 watts. They should have a dummy load, but, the fact is that the majority of operators don't have any dummy load.

    Glen, K9STH
  15. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Which helps re-define the "dummy" part.:):p
  16. AE5JU

    AE5JU Ham Member QRZ Page

    I just fired up my new AL-811H for the first time tonight. I am using the ARB-704 relay buffer between the amp and Icom 718. The 718 is connected to the radio via the 13-pin cable going into the radio's Accessory Socket.

    At first I couldn't get any power out... then it dawned on me. I had the ALC cable hooked up. Unplugged that and Voila!

    I'll hook that back up and adjust the ALC pot later, but for now I was able to get it up to 825 watts with just under 60 watts of drive.

    I've got some Svetlana 572B's in it for now.

    Backing off to 45 watts from the IC-718 gives 700 watts out. At that level I'm showing about 500 ma plate current and 90 ma grid.

    Once I get this sorted out I'll replace the 572B's with the original 811A's and back down the drive to run it at a lower level.
    Last edited: Nov 22, 2009
  17. N4CR

    N4CR XML Subscriber QRZ Page

    That's probably a good idea. Lots of hams put in 572b's without resetting the neutralization and you can get into some ugly situations by doing that. The original tubes are plenty good to last a long long time. Decades if tuned properly.
  18. W5DWR

    W5DWR Ham Member QRZ Page

    Thanks for the info.

    Thanks AI4OF for that tidbit about the 572 tubes. I put some in my 811H and it just seemed to be a little off, so I got suspicious about what was happening inside. I have since replaced them with the 811As that were in it when I got it and it works like it should.
    Thanks again.
  19. NS8N

    NS8N Ham Member QRZ Page

    I disagree sir. Many have one but they do not know it. They may call it by another name like "radialless, base fed vertical antenna" or other such.
  20. W8JI

    W8JI Ham Member QRZ Page

    Despite MFJ's QC reputation, nearly all initial problems are due to operator error or overlooking something. It has always been that way.

    I would check for:

    1.) The RF input and output cables being swapped around

    2.) ALC connected and adjusted wrong

    Based on the description the plate current came up and the LED came on and he could transmit through the 811 in standby, there are a very limited number of things that could be wrong.

    External to the amp, only two things above.

    Internal to the amp, something with the tuned input board.

    .....and of course the #1 thing with anything new, operator error.

    73 Tom
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