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High Gid Current

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

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  1. NE7X

    NE7X Ham Member QRZ Page

    Measure the plate meter resistance.
    I did answer this question, using my Tektronix DVM with all wires disconnected from the plate meter, the coil resistance is: 51.8 ohms
    If this is not what you are asking for, please give me more clarification.

    How do I measure the BIAS feed-through C33 break down voltage? What method do I use? Since the ALC feed-through is the same value, would swapping the ALC feed-through with the BIAS feed trough answer this question?

    As for the chassis grounds, this was one of my first questions I asked about at the beginning of this forum. There could be some ground difference between the top RF deck, meter circuit front panel and power supply bottom (three separate chassis). I did check with an ohm meter and it "appears" the grounds between chassis are all zero ohms. However I guess since .2 ohms are used for shunts, a .1 or .2 ohm ground difference between different chassis could make a big difference. Tonight I will add some additional parallel ground connections between all the different chassis ground points.

    You’re at a loss !!! So was the guy I got the amp from and so am I. This now makes three of us. Remember, the guy who I got the amp from was fighting the meter circuit issue for 6 months before he gave up and sold me the amp.

    It was mentioned on this forum before by others, the issue is most likely a 1-in-10000 odd-ball issue that probably will never happen again on another Henry 2K Classis amplifier. Need to start looking outside the meter circuit, going in circles focusing only on the meter circuit. What other circuits would cause the meter circuit to display this type of activity?

    Thomas NE7X...
    http://ne7x.com
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    For one thing I would by pass the switch. Hey at this point we cannot leave a stone unturned. You never know what could be going on insside that switch, after all it is in the circuit NO? If there is a second cap that is the same as C33, I would switch them out to eleiminate that as an issue.
     
  3. K9ASE

    K9ASE XML Subscriber QRZ Page

    I'm wondering about the meters themselves. I think it was mentioned earlier that they are identical part #'s I wonder about switching places with them and see if the problem reverses.
     
  4. NE7X

    NE7X Ham Member QRZ Page

    W1QJ

    I'm at work now :p so tonigh when I get home I will:

    1) swap the ALC and BIAS feed-throughs caps
    2) Bypass the meter switch and connect direct
    3) Add 1/4 inch ground strap between all three sub-chassis grounds.

    I will update this fourm once I have performed these steps.

    Thomas NE7X....
    http://ne7x.com
     
  5. W1QJ

    W1QJ Ham Member QRZ Page

    It is pretty easy to test a meter. Use the shunt used in the circuit and any series resistor and set it up in series with a known meter. use a battery and a resistor and pot and set the known meter to the full scale reading of the meter. When the full scale current is reached on the known meter the other meter should read full scale also if the shunt and series resitors are correct. It is a simple bench test that will check all parts concerned at once. I have seen meters that have taken a whack and instead of opening up, the resistance changes. Many of us tap a meter with an ohm meter and if the coil proves OK because the meter moves we think it is good. I thought we were going for coffee but instead we are back to work.
     
  6. W8JI

    W8JI Ham Member QRZ Page

    Tom,


    Sorry I missed the resistance of the plate meter.

    If the plate meter is 50 ohms, which most Beede 1 mA meters were, the proper multiplier resistance for that meter is 150 ohms.

    That will make the 1 mA meter read 1 amp full scale with a 0.2 ohm shunt.

    Now if we look at the Henry original schematic, I wonder if the wiring was all totally wrong around D107 and R119. it is pretty off they labeled the multiplier R115 0.2 ohms, and then had the correct value off by itself labeled as R119 but not shown connected as a multiplier. What are the odds of having the right size resistor randomly used in some nonsense place? More likely the wiring was nothing at all like the schematic.

    If you want, bring it to Georgia. We can fix it in no time. :) I am virtually certain you have a disagreement between the schematic I drew and what is really in the amp, although there could be a bad ground or bad component somewhere.

    To check the capacitors for breakdown voltage, you can use a 50-150 volt supply and limit it with a current limiting resistance. You really need to have a variable voltage supply anyway for testing zeners and other things. Get yourself a cheap 24 volt AC wall wart or doorbell transformer, and voltage double the output. Then you can run it up or down with a variac, or put a big pot on the output. Then you have a ~75 volt low current supply that you can use to find the voltage of zeners and for testing low voltage caps.

    Cutoff bias on a 3-500 is 30 volts or so, so if the filament bypass caps hold up to that without drawing current from the supply they are good.

    I'm surprised with all the stuff you collect you have never found an old Eico or Heathkit capacitor bridge. :)

    If you want a vacation, bring the amp over. If you want to trouble shoot it over the phone, call me. It will be faster than all this typing.
     
  7. NE7X

    NE7X Ham Member QRZ Page

    W8JI

    Your comment is Interesting. You say the proper multiplier resistance for a 50 ohm 1ma meter should be 150 ohms. If you look at the Henry PDF schematic, it shows a 150 ohm resistor R119 in parallel with D107 diode, then both are in series with the plate meter M101 (Ip). Currently R119 and D107 are removed. As you know there are several other errors in this schematic, Could this also be an error where multiplier resistor R115 is actually 150 ohms? Right now both R116 and R115 are .2 ohms. Should I try replacing R115 with a 150 ohm resistor?

    Currently both meters appear to be working, it more like they are "to sensitive" and then peg when giving full 100 watts drive. Maybe its the multiplier resistor? I also wondered about the voltage divider R117 & R118. If their values were incorrect, would this cause the meters to be over sensitive?

    I do have an old Heathkit IP-17 A/ B+/B-/C+/C- variable workbench zero to 400 VDC power supply. I will disconnect all the wires on C33 and then connect the power supply across C33, and slowly turn up the voltage, stopping at 150 VDC maximum, which watching the current meter on the power supply.

    Funny that you mention capacitor bridge. Yes I do have an old Eico capacitor bridge, one with the cat eye. Let me dig it out of my storage bin.

    It would be nice to bring the Henry over to your QTH and work on it together. I'm sure the problem would be resolved in minutes and we would probably also have several other circuit design improvements installed before the coffee got cold. However at 185 pounds I think the airline would charge me a huge check-in luggage fee. HI HI

    Let me play with a few things for now, then if I am un-successful, maybe Sunday afternoon or evening this weekend if you have some free time, I will call you on the LL and you can walk me trough a few troubleshooting steps. I totally agree, troubleshooting this issue via emails and chat forums has lots of gaps in real time communications, mis-understanding and assumptions.

    Thomas NE7X...
    http://ne7x.com
     
  8. NE7X

    NE7X Ham Member QRZ Page

    *** GOOD NEWS *** Half way there !!!


    I now have the Plate Ip current meter M101 working near perfect. I changed out the .2 ohm multiplier resistor R115 with 150 ohm resistor and now the plate current meter no longer pegs full scale with 100 watts drive

    Key, no drive = 40ma
    Key, 100 watts drive = 460ma

    I don’t think the meter is calibrated correctly. Compared to my Henry 2K-4 and 3K-A,

    Key, no drive= 200 ma
    Key, 100 watts drive = 800 ma

    I believe I need to play with different sizes of the multiple resistor values to get the meter calibrated correctly. However this is a very positive sign.

    Now the BAD NEWS, the Grid Ig current meter still pegs full scale. My assumption, it also has a multiplier resistor, R117, and it may need to also be adjusted. The current resistor value is 30 ohms. So now I am going to play around and see what happens if I increase and decrease R177 value.

    QRX… more to follow…..

    73s, Thomas NE7X…
    http://ne7x.com
     
  9. W9GB

    W9GB Ham Member QRZ Page

    Tom -

    Great News !

    As you stated earlier, the Henry amplifier is now operating properly ... proper tube color, correct RF output - externally/separately measured.
    Now it is a matter of selecting the proper values of R115 (plate, Ip) and R117 (grid, Ig) for the Henry panel meters (M101, M102) to read correctly (with their factory meter scales).

    Awaiting wrap up !

    w9gb
     
    Last edited: Jun 16, 2011
  10. NE7X

    NE7X Ham Member QRZ Page

    I believe I have everything working now. Its looks like the root of my meter pegging issues was with the “multiplier resistors” for both meters. Here is a drawing of how I have the meter circuit wired and the resistor values which gives me the following reading with 1KW output on 20 meters into dummy load.

    2K_Classis-meter-wiring-NEW.jpg


    Key, no drive: Ip = 50ma / Ig = 0ma
    Key, 100 watts drive: Ip = 700ma / Ig = 250ma

    I have no idea if these reading are correct or not. However comparing them to my other Henry 3-500Z grounded-grid amplifier readings, the readings appear to be at minimal “in the ball park.” I also noticed, depending upon the band, the “key with 100 watts drive” values vary. Some bands the values are higher and some bands the values are lower. However the readings for all bands are within the meter scale, no pegging of the meters.

    At this time I believe all the issues have now been resolved and the amplifier appears to be running as expected. Here is a list of the items I discovered in repairing this “basket case”

    1) Bad ground for band selector switch door-knobs
    2) Roller induction wheel arcing to shaft
    3) ALC HV diode shorted
    4) BIAS zener installed backwards causing tubes to run hot
    5) Ig meter was pegging full scale, rewired meter circuit per W8JI’s recommendation
    6) Adjusted meter multiplier resistors to get Ip and Ig meters to read correct and not peg full scale.

    My next plan is to put the amplifier mechanically all back together, then perform some stringent testing over this coming weekend. Work some DX on 20 meters and some long winded rag-chews on 40 meters. Assuming the testing period passes, I will then write up everything in a nice summary website, including pictures and drawings. You will be able to find all this information off my home webpage: http://ne7x.com

    Thanks to everyone for your time helping me with get this basket case working. A special thanks to my childhood friend W8JI for providing me with the metering recommendations and discovering the zener ordination issue. However without “everyone’s” help, suggestions, ideas and positive attitude on this forum, I would most likely be putting it up for sale like the guy I purchased it from. HI HI

    73s, Thomas NE7X…
    http://ne7x.com
     
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