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Some Sb-220 Questions.

Discussion in 'Amateur Radio Amplifiers' started by KJ4AQU, Apr 28, 2014.

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    That's fine
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    With the AL-82 Tom had a continuous flat copper strap about the width of RG-58 braid and he went all around picking up all the ground points with one piece. Probabaly not needed, but I can see the thought behind it. No big difference I suppose unless he had a motive I am not aware of. He designed a new 3-500 socket that has a ground plane and the whole socket area is grounded. Pretty need way to get low inductance grounding.
     
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    I think the socket grounding is a good idea, like the 44CX250 sockets you can get that have all the cathode pins ground to the metal flange. The Johnson sockets used by Heath pose a different geometry, and their mounting requires fiber washers in order to keep the ceramic from cracking. I believe Tom's sockets are fiberglass, and lower profile...
     
  4. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    Sorry another question! I noticed on my Grid/HV meter there are 2 back to back diodes to act as meter protection. However, there are none on the Plate Amp meter. Should I add them? I have the older Harbach meter/rectifier board
    that do not include them. Thanks in advance.
     
  5. W1QJ

    W1QJ Ham Member QRZ Page

    I am not sure if his board will protect both meters cause I never looked at a schematic of his board. But I suppose it can't hurt to have a redundant set as long as the meter accuracy is not compromised. All his boards have meter protection but like I say I am not sure if both meters get protected.
     
  6. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    Ok I Put diodes across plate meter as well. My older meter board does not have the meter protection diodes on it.

    Ok bit the bullet. Wired the HV to the insulated connector.

    Hooked up my trusty old IC-756 to the amp using a Relay buffer (just because) and started at 80m and worked my way up. In CW mode got around 950w out at 80m and 40m. At 20m 1KW! And yes it gets more tricky to tune!!! at 15m maybe 600w 10m almost 150w I think the input coil may need some tweaking on 10m. At the lower bands 80,40,20 got the tubes nice dull red/pinkish color.

    All this into a 1.5kw Dummy load.

    Maybe a late question but what are the max plate/grid currents allowed to be? I was thinking plate at 750mA and the grid around 250mA does this sound about right?

    Also on the low power side (CW/Tune) the HV was at 2600 resting. When keyed maybe 2300 so not loosing to much there.

    So it is more or less working ok except for 10m which I most likely wont use anyway. Mostly I am on 40m,20m.

    Oh and there was no arcing or sparking to the screen cover at all. Tune cap seems be ok no coronoing at all had one plate on it that was rough and jaggedy to used my dremel with a fine grid sanding wheel and smoothed it out. Also these tubes stink when heated...Geez! :)
     
    Last edited: May 14, 2014
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Copper flashing (solid copper strip, not woven nor braided) certainly has lower inductance than woven or braided materials of the same width, so that may have been the motivation.

    In my 4-1000 6m amp, I found the connection from the chassis to the front panel was critical, since the TUNE and LOAD controls were mounted to the front panel and not the chassis. I tried using a few pieces of 1/2" wide copper braid for that, but not so great. It was still unstable until I replaced the braid with solid copper flashing. All instabilities gone forever.

    I'm not much of a fan of "braid" for anything critical. Oxidation occurs on the strands that insulates them from one another, and then you have hundreds of pieces of very skinny wire in parallel, and nothing like the width of the original material. And that seems to happen really fast, even with "tinned" copper braid, because the "tinning" is on each strand and not the bundle.

    Silver plated braid isn't any better; it might actually be worse. Raw copper is definitely not so good, as copper oxide is a great insulator and that happens starting about one second after it's exposed to air.

    Ditto aluminum. I remember a great friend of mine was a Ph.D. metallurgist and I asked him how long it takes for oxide to form on aluminum.

    His answer was, "Well, in outer space, maybe years or centuries. Here on Earth, about a few milliseconds."
     
  8. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    Hey Steve, How about a sheet of copper and cutting strips of copper from it to form the grounding instead of the braiding? I can get sheets of copper pretty cheaply at my local electronics surplus store. Thickness around .007 Inches. Would that be good to use?

    Frank
     
  9. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    also regarding the copper strips. Better to directly ground them or can I solder to the ground lugs? Would make it a little easier. Again opinions desired.
     
  10. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    Copper strips added. Braided cable removed. The copper strip is .007 in thickness. Will it be thick enough?
     

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