High Gid Current

Discussion in 'Amateur Radio Amplifiers' started by NE7X, Jun 5, 2011.

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  1. W9GB

    W9GB Ham Member QRZ Page

    1. CHECK C8, and see if it is bad, burnt or cracked.
    2. CHECK Bandswitch wiring from tap of L4 coil to the bandswitch section.

    Tom -

    For reference purposes, this is Henry's floor console Classic 2K model, right?

    As I read the Classic 2K manual, for comparison purposes, where was the SSB/CW switch set? SSB ?

    What has the Plate Voltage been reading on the meter?

    Did former owner ADD the 10 meter parts for this amplifier?
    Henry manual states that 10 meter amps were not installed at factory for US domestic models.

  2. W8JI

    W8JI Ham Member QRZ Page

    Here is the RIGHT schematic, it is the second one I posted. The meters are not in series.:


    I am 100% sure this will work.

    Tom, the Zener cannot cause your problem. Not in any way can it be a problem for meters, unless it is accidentally shorted to ground or you have some wiring error!!!!!

    R118 is required to develop the voltage from grid current. How it works is shown on my website:


    Here is a block of how it works:


    Tom, let's make two assumptions:

    1.) The meter is reading correctly, but you are pinning it. This could be because you have the amplifier tuned wrong. If you have the loading control set too light (too much capacitance) the grid meter will run high. This also means you are splattering.

    2.) The meter is reading wrong. This means you have a wiring or component problem of some type. If the SHUNT going to ground is 0.2 ohms, it will produce .02 volts for every 100 mA. To read 400 mA FS we need .08 volts on the meter. If the meter is a 50 ohm 1 mA movement, the basic meter is .05 volts so you need an additional .03 volts at 1 mA. That is a 30 ohm resistance.

    There is nothing else possible Tom. You could be mistuning the amplifier. That will make the grid meter pin. It is damn easy to get 400 mA on two 3-500's if you tune wrong.

    Or your meter is not really 1 mA 50 ohm, or you have a wiring error from what I drew.

    It cannot be bias, it cannot be anything else. It can ONLY be what I said above.

    73 Tom
  3. W8JI

    W8JI Ham Member QRZ Page

    Double post. I deleted it. Weird>
  4. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page


    You have at least improved! Going from nothing to "double for your money"! :rolleyes:

    Glen, K9STH
  5. NE7X

    NE7X Ham Member QRZ Page


    Yes, you are 100% correct, it was the loading on 15 meters. I played around with different setting, low and high capacity, and now the grid current meter is no longer pegging on any band, including 15 meters. So I guess it was operator error. I tested again on all bands. The Ip current in the HV setting runs +/- 600-800ma and the Ig current is running +/- 150-300ma (depending on where I have the loading capacitor set) with 100 watt carrier drive.

    Here is how I have the meter circuit wired


    73s, Thomas NE7X…
  6. W8JI

    W8JI Ham Member QRZ Page

    Good! I never initially considered misadjustment of the loading cap. With a 400 mA meter scaling, it is easily possible to peg out the grid meter with two tubes, because typical carrier grid current at optimum efficiency is 125-175 mA per tube at 3000 volts on the anode, and even more when at lower anode voltages.

    So now we know the meters are working properly, they are reading the real currents, and so on.

    My only other suggestion is a bit more capacitance across D106 to slow transients down, and to bypass 80 meters better. I would use a 0.1 uF disc cap.

    The initial circuit, as DRAWN by Henry, never could have worked!!! I see how they got into that mess of parts, because of the 25 ohm resistor in the B- rail. I would still be sure to add the surge limiting resistor in my drawing.

    73 Tom

  7. W8JI

    W8JI Ham Member QRZ Page


    Does Fred know QRZ is now impossible to use with IE7 on reply windows?? The Window jumps around. On Firefox it is stable, but IE7 is useless.
  8. W9GB

    W9GB Ham Member QRZ Page

    It is very possible that the builder / designer and the perosn that finished up / drew final schematic were not the same person.
    This is ALL to COMMON with technical documentation -- software doucmentation (or lack of) is even worse !

    That is the tough part of remote / Internet troubleshooting -- so many minor details are ASSUMED.
    ... and it would take too long to type responses to go through all of them !

    Spelling checker does not work, either.

  9. W1QJ

    W1QJ Ham Member QRZ Page

    I ass(umed) that loading up the amp would not be the problem. I am ass I suppose. Can we have coffee now?
  10. NE7X

    NE7X Ham Member QRZ Page

    OK everyone, I think we can now officially close this forum, the Henry 2K Classis is working perfect. I performed more testing last night, on all bands. I am getting a full 1KW+ out, all meters are reading within mid-to-high-mid ranges on the scale with 100 watts carrier driver, I get a very nice Ip dip and the tubes are running a nice soft rose pink color.

    Today I will start re-assemble all the sheet meter, shields, cables, and cabinet parts, putting this basket case back together. I will also change out C114 from a .01 to .1 capacitor, and then add the 175P 35-40 ohm HV limiter resistor(s).

    Again, thanks everyone for working with me in getting this amplifier working. I learned a lot and now have a much better understanding on how grounded-grid BIAS and metering circuits work. This has been an outstanding learning experience to say the least.

    On the topic about QRZ issues, yes I have also been experiencing the same for me. I personally know Fred. I have worked with Fred professionally at both Intel and IBM supporting high-end UNIX servers for many years, and I see/talk with Fred at just about every local Phoenix area hamfest. I will inform him of all the issues everyone has mentioned.

    73s and good DX. Have fun and enjoy the hobby!!!

    73s, Thomas NE7X…

    PS: Watch my personal website. In the next few weeks I will compose and post a web-page with all this Henry 2K Classis information.
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