What's wrong with those porcelain plate grips?

Discussion in 'Amplitude Modulation - AM Fans' started by K5UJ, Sep 7, 2017.

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  1. K5UJ

    K5UJ Ham Member QRZ Page

    I always thought the porcelain would inhibit heat dissipation, acting like an insulator, not only for electricity but also for heat. Another thing I don't like about the porcelain is the contact surface. On the sides, the strip insert is flat but the plate cap is round. On top the insert strip is flat and if the plate cap is the original solder job, probably flat enough, however the wide round spring clips wrap all the way around the round cap, providing a large contact area, almost the entire side of the plate cap.
     
  2. WA3QGD

    WA3QGD Ham Member QRZ Page

    Never had a problem with em,then i don't Twist them off. a vertical Rocking slightly up and down with pressure on the tube downward to debond the grip after its sat for some interval seemed to work,but if my own ham handedness didn't take out the tube it was on it's way to the roundfile anyway.besides it's a poor carpenter that bemoans the sharpness of his tools.
     
    N2EY likes this.
  3. AC0OB

    AC0OB Subscriber QRZ Page

    Here is what I am currently doing to make plate caps:

    Plate cap 380 ACP Cartridge.jpg

    For the smaller power tubes, such as the 2E26, 6DQ5, 6DQ6, 6146, etc., I take a new, clean .380 Auto Cartridge above (.380 ACP, 9mm Kurtz), and cut it down to about 0.340" overall length with a Dremel grinder disk, then the three sides are split 120 degrees apart with the grinder disk, to about a 1/4" from the rim or base. I finish it up with sandpaper to remove any burrs. With a needle nose pliers, the splits or ears are bent to just effect a light grip. My parasitic choke is then soldered to the top (primer) hole with silver solder.

    For the larger plate caps, for example the 813 etc., I use a Government 50-70 cartridge. This cartridge is cut to about 0.625" overall length and the same procedure is applied as above.

    I then apply a very thin film of VersaChem Spark Plug Boot Grease, Part No. 15309, with a Q tip to the inside of the cartridge to reduce any oxidation and to reduce the removal or pull force.

    These cartridges can obtained from Starlite Brass, Bell, Federal Cartridge Company, Winchester, Midway USA, and other suppliers. If you have a friend who reloads firearm cartridges, ask him if he could do the cut-down and trimming.


    Phil



     
    Last edited: Sep 13, 2017
  4. W7TFO

    W7TFO Subscriber QRZ Page

    A real bang-up job!

    73DG
     
  5. WB2GCR

    WB2GCR Ham Member QRZ Page

    think you meant cut-off disc for the slitting?

    I'd probably want to make the slit longer than the height of the plate cap by 25% or more...
    An "O ring" around the assembly might be good to maintain contact... especially if the cap
    gets pulled on and off... that's the same deal as used on RCA plugs.

    Maybe the ID of the RCA plug will match a tube cap?? That would be most convenient!
     
  6. AC0OB

    AC0OB Subscriber QRZ Page




    Many variations on this theme is possible.:)

    Either disk will work. The cut-off disk makes a narrower slit.

    If you want to cover the whole cap say for a 6146 or 2E26, one cold cut it to a total length of 0.45" or so.

    For an 813, a cut length of 0.75" or so would work just fine.

    The important thing is to find a cartridge that has an ID close to the OD of the tube cap.


    Phil



     
  7. K5UJ

    K5UJ Ham Member QRZ Page

    I'm trying to figure out the metal National used to make their Grid Grips. The small ones for 807s seem to be some kind of nickel -- same metal all the way through. The large 810 size look like some kind of brass plated with nickel. I can get sheet metal of beryllium copper or nickel silver. It's expensive metal though, which may explain partly why you can't get these things today. The b.c. sheet metal is supposed to have springy property.
     
  8. WB2CAU

    WB2CAU Ham Member QRZ Page

    Okay, I know steel is not considered good engineering practice, but stainless steel should okay, yes? Depending upon the grade of stainless steel, it usually doesn't have magnetic properties.

    There are mini hose clamps available in an assortment of sizes. I think at least some are available in stainless steel. I didn't see anyone mention that yet in this thread. Granted, there might be cases where it's inconvenient to get a tool into a tight spot to loosen, but if home-brewing, you can make accommodations ahead of time for that.
     
  9. K5UJ

    K5UJ Ham Member QRZ Page

    s.s. may not be magnetic, but it has other problems. It can be hard to work because it is a hard alloy, and you pretty much can't solder to it. But you can make a physical clamp bond as you mentioned with a hose clamp. s.s. does have iron in it, so it may heat under RF conduction. But I'm not certain of that because I have not tried it. Probably the biggest downer with stainless steel is that is sucks as a conductor compared to copper, aluminum, and other common RF conductors. S.s. has 40 times less conductivity as copper. You might clamp a copper strap to an anode cap with it but then you may as well loop a copper strap around the anode and tighten it with a brass nut and bolt.

    I've heard of stainless steel hose clamps used in a pinch to make exposed anode plate blocking caps for FM rigs. You have a tube like a 4cx2500. You cut and wrap some aluminum or copper strap around the outside anode fins, then a couple layers of Kapton tape, and another strap of metal on top of the tape and clamp the whole thing down with a pair of hose clamps. You have your 10 KV plate blocking cap with the Kapton dielectric. You have to have a way to measure the capacitance and keep adding Kapton until you get close to the value of the stock cap. Fast way to get a rig up on a mountain back on the air until the manufacturer part can be put in.
     
  10. K9STH

    K9STH Ham Member QRZ Page

    I use stainless steel hose clamps for the cathode connections in my 160-meter linear amplifier that has 2-each GI-7bT tubes. They are connected together with an aluminum strap and then the r.f. input (the amplifier is grounded grid) is connected through a machine screw in the aluminum sheet.

    http://nebula.wsimg.com/c860894a9c3...50C433DB440D6B60D&disposition=0&alloworigin=1

    One of the photographs is the underside of the home brew tube socket assembly.

    Glen, K9STH
     

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