FL2100Z - using 811A

Discussion in 'Amateur Radio Amplifiers' started by VA3QY, Jul 7, 2020.

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  1. VA3QY

    VA3QY Ham Member QRZ Page

    I received a set of chinese 572b directly from china. looks identical to the cetrons. Will plug them in and see how they work.

    Prices are going up. Is there a supply problem in china? Svetlana is impossible or very pricy to get.
  2. VA3QY

    VA3QY Ham Member QRZ Page

    thank you roger. i was going to open it on the weekend. to inspect and test the 572b received.
    I was going to drop a couple of drops of oil for the band switch and the fans.
    I tried to see the manual on process on replacing the tubes; not sure it talks of shorting the capacitors; using a screw driver?

    What else you would recommend me check? I can look up the serial number to see date of prod; it appears to be very clean and no mods done. I was also considering replacing the caps on the transformer but again, do no harm unless required is my motto.
    Last edited: Jul 22, 2020
  3. VE7DQ

    VE7DQ Ham Member QRZ Page

    It's interesting that in the August 2020 QST there is a reprint of an October 1970 'Beginner' amplifier with a 2400 VDC power supply that used an 813, 803 or a pair of 811s. I guess Lew McCoy could get away with it in 1970 but with today's import tubes from who knows where ;) it would not be prudent.
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    (2) 811A's, even if they were real ones, is still not very much dissipation. As Roger @G3YRO stated, you would be better off with one 572b.
    VA3QY likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No, it doesn't.

    If you read the article, under Which Transformer?, Lew describes that the 811A version works at 1500Vdc and discusses using a 500-600V transformer with a voltage doubler. He never discusses using 2400Vdc on 811As.

    Gotta read the whole article.
  6. G3YRO

    G3YRO Ham Member QRZ Page

    Don't just oil the fans, take them out, take them apart, and clean them properly with White Spirit (it's very easy) . . . they tend to get gunged up with dust and gunge sticking to the oil.

    Then lightly oil the bearings when you re-assemble them. (this is best done every 5/6 years)

    Roger G3YRO
    VA3QY likes this.
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Many of the Svetlana 811's are not for transmitter duty. They are made for the hi-fi market and will not cut off properly and certainly can't take serious HV (even less than the Chinese 811s).

    The 572s you found sound like the same ones that RF parts gets, without the warranty, which, if they work, will probably work very well. Get them while you can. There are some serious problems going on over there even before the Covid mess.

    Do this to the original fans to clean them up. It's an easy task.



    WD-40 on a lint-free Texwipe cleans all the gook off. My favorite oil for sintered bronze bearings is PDP65, which is used in tape machine capstan motors by Studer (The Swiss have good taste in hypoid gear oils). Air tool oil or sewing machine oil also work well for this task. The felts and little pores in the bearing get clogged up by detergents in regular motor oil, scoring the rotor shaft eventually.

    When putting the motor together, make sure the rotor is centered in the stator. After this, a couple drops a year in both felts will do nicely.
    VA3QY likes this.
  8. VA3QY

    VA3QY Ham Member QRZ Page

    Thank you roger and chris!. This is truly what the doctors order. I will do it as you suggest.

    Roger on the C222 : i ordered 2 of the following caps based on earlier read ups -

    1000pf/12kv and based on dimensions it should fit; true i may have to do some juggling on the screws.

    Attached Files:

  9. VA3QY

    VA3QY Ham Member QRZ Page

    I spoke with a couple of retailers from China; all are complaining there is an issue with stock for 572b tubes. Not sure how long this will last though.
  10. VK4TI

    VK4TI Ham Member QRZ Page


    I have been wondering if I can replace 572b with 811a? It is a question as I can drop 572s into 811 why not vice versa - yes power output will be lower.

    What is required to make FL2100Z to work with 811A?""

    GI7B is common conversion , cheap from Dr Alex

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