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fl-2100b doorknob caps

Discussion in 'General Technical Questions and Answers' started by WB2BM, Apr 12, 2008.

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  1. WB2BM

    WB2BM Ham Member QRZ Page

    Need a 1000pf doorknob capacitor. it calls for 3k caps. Could I use a cap with bigger voltage ratings or does it have to match perfect?
  2. W9GB

    W9GB Ham Member QRZ Page

    Should be an "off the shelf" part from RF Parts.

    Tell them you need the part for a Yaesu FL-2100b amp, and they should be able to get you right part.
    Other choice is "hit or miss" at dwindling hamfests, eBay from Chinese/Taiwan mfg. / suppliers or the surplus stores (Surplus Sales of Nebraska and others across US).

  3. K3WRV

    K3WRV Guest

    If you have a cap with a higher voltage rating, it should work just fine, IF IT WILL FIT!!!. But try to keep the capacitance about where it's spectd to be. (~1000pf). I assume by 3K you mean 3KV.
  4. WB2BM

    WB2BM Ham Member QRZ Page

    Thanks for the info I'll check RF parts. I see lots of 1000pf caps none with 3kv ratings they range from 4kv and up..
  5. W9GB

    W9GB Ham Member QRZ Page


    A voltage rating higher than 3 KV is OK ... BUT you want to check the size --
    if clearances are an issue for your amplifier.

    I see in Carol Maher's notes (Fox Tango) that your part (C222) is:
    Yaesu part number: K24356102 - RDA30 3 KV
    Check with Yaesu parts or Carol for that part as well as RF Parts

    Scroll down to FL-2100b photos for a specific photo of that part: Amplifier Evolution.htm

    HT-50 / 58 Series
    Ceramic doorknob. 0.813 inches diameter,
    0.89" long. 6-32 UNF thread.

    HT-50 series at Surplus Sales of Nebraska

    HT-50 series at RF Parts

    Yaesu FL-2100 Technical Bulletin - when using Svetlana (SED) 572B tubes
    Bias Level Adjustment kit is ONLY $ 2.50 from RF Parts!

    IF you want to buy the Chinese product, look at eBay item number: 250234992793
    1,000 at 15 KV .. measurements 30mm diameter, 21mm height.

    Last edited: Apr 13, 2008
  6. WS2L

    WS2L Guest

    How do you like that amp ? I'm going to look at one this week that I will probably buy.
  7. W9GB

    W9GB Ham Member QRZ Page

    Dave -

    If you are going to purchase a Yaesu FL-2100b, I would recommend listening to Steve (WIK) comments as well as those of Carol Maher at FoxTango.

    Scroll down to the FL-2100b section of the Yeasu amplifier page at FoxTango, where Carol provides service comments with photos.
    A common problem is the band switch on these units. Yaesu released a service bulletin (CA:128) on this issue in 1977. Amplifier Evolution.htm

    In addition, since most amplifiers of this vintage are now 30 years old -- some common sense maintenance and updates are highly recommended.

    1. Replace high voltage electrolytic capacitors
    2. Clean bandswitch, fan and inside of amplifier
    3. Check R207 (47 Kohms), see Carol's notes
    4. Check C222, photo here (K24356102 - RDA30 3 KV): 572B Finals.JPG
    5. Check RFC, here are side-by-side photos of a destroyed RFC on left and new one on right. Overhaul.jpg

  8. N8YX

    N8YX Ham Member QRZ Page

    If RF Parts doesn't have what you need in stock, PM me. I just picked up half a dozen or so at our last area hamfest...
  9. WB2BM

    WB2BM Ham Member QRZ Page

    I like the amp so far. Got it off of ebay. Aside from the #222 cap being cracked. Very easy to work on, lots of room inside.
    I just got done cleaning and oiling the fans. They probably didnt need it as there was hardly any dust on or in them, but they got some fresh oil and do spin faster now. The band switches are still in good shape and it has cetron tubes (could be original). Puts out 900+ watts, I dont want to push the cap to much till I get a new one installed. Its also wired for 110v. I do plan on running a seperate 220 line for it. Also plan on getting 2 new tubes and packing up the old ones as spares. Hopefully it does me right..
  10. WB2BM

    WB2BM Ham Member QRZ Page

    Thanks n8yx,
    I will know monday when I call thanks for the offer!!:)
  11. WB2BM

    WB2BM Ham Member QRZ Page

    Does any one know how to get in touch with yaesu parts? Or do you have to go through a dealer. I wonder if parts are gonna be super hard to find for this box. Looks like Fred is gonna bail me out for now..
  12. W9GB

    W9GB Ham Member QRZ Page

  13. W9GB

    W9GB Ham Member QRZ Page


    There are Chinese mfg. who make HV doorknob capacitors. One eBay seller is: yishdz

    Their 1,000 pF 50 kV doorknob is currently listed as item number: 250217839777 at $12.50 plus $7 shipping.
    I have not heard reports on quality (good or bad).

  14. K4AVL

    K4AVL Ham Member QRZ Page

    I restored one of those last month, and RF Parts has those (higher voltage a bit) but they are small enough. They may not have the same threads (or male/female threads) the same way, so you may have to improvise. They do have used "pulls" of these too for $9.99 which is not on their online catalog. The FL2100b has at least 4 doorknobs in it, you may want to check the others too. One in the grid section, and two at the left of the case, next the the left 572B at the case wall.
    The two at the left case are in parallel, and I believe add up to 800Pf, if I recall. These looked good to me, but one of these pulled apart on me, having been exposed to a lot of heat for a long time. So wiggle those too with a little strength and see if they are ok. I replaced the one that broke with a ceramic RF cap, not a doorknob, and it worked fine, and it's ok to be off 100 Pf or so on those, but I wouldn't skimp on the one in the plate circuit. Also, be sure to check the parasitic resistors as well for heat damage and replace those too if need be. There are also mods on the foxtango site using nichrome strips, etc.
    Good luck.
    The one I got was from an SK, but you have to be careful with parasitics on these, just tune up carefully.
    Also, if you use 240v, set the jumpers for 234 so as not to have too high HV, it should be under 2500v, not 2600 or so you may get if the jumpers are set wrong. Same is true for 120, use the jumper settings for 117 and not 110, the prolong the life of your tubes & the unit in general.
    Last edited: Apr 17, 2008
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