572 tubes update

Discussion in 'Amateur Radio Amplifiers' started by W8JX, May 15, 2015.

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  1. W2VW

    W2VW Ham Member QRZ Page

    Time to figure out how to wedge a pair of 813s into those old Green amps. Maybe a small toroidal filament transformer...........................
     
  2. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    So that's why 572's have some getter on the glass. I've been wondering about that...
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    572Bs don't have getter material deposited on their anodes at all, unless someone invented a new process.

    3-500ZGs do, it's zirconium and has been used to getter those for a long time.
     
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Do you know what the Cetron plate is made of? It looks machined and I just assumed it was graphite. Thanks for the edumacation. There's a bent element in this one. I wish I could reach in there and straighten it out!
    IMG_1046.JPG
     
  5. VE7GPG

    VE7GPG XML Subscriber QRZ Page

    your bench looks a lot neater than mine !!!!
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    As I understand it, later generation 572Bs have a graphite anode with a titanium getter. However, it wasn't always that way.
     
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hi GPG.
    2 benches in heavy rotation here. Large power amp on this one is a problem child... I'll clean that down with a snow shovel when it's done Monday. It will be disaster on Monday afternoon again. No rest for the wicked! That razor blade on the right is just in case I have to end it all...

    Thanks WB2WIK.
     
    Last edited: May 17, 2015
  8. G3YRO

    G3YRO Ham Member QRZ Page

    Yes I always thought the Cetron 572Bs (and their excellent Chinese copies) had carbon anodes?

    On the subject of these valves, in my experience it's very strange how they seem to go wrong . . .

    They just seem to stop working . . . ie the filament still glows, but one valve ends up doing all the work (which you can tell as one has its anode glowing red, while the other looks cold). And when you swap them round it's still the same valve that doesn't do anything)

    The standing current drops to half normal value . . . you can only get half the input power . . . and the output obviously drops to about 250 - 300 watts.

    Can't see anything wrong looking inside the valves. (unlike some line output valves used in PAs and Linears, like 6KD6s, where you can see the thin wire from the anode to the top cap is broken - I think by design, as it acts as a fuse to protect TVs)

    This has happened 3 times with my Linear (about every 15 years) . . . and each time I've replaced BOTH 572Bs with a new pair (always Cetron, but Chinese the last time)

    This is in a Yaesu FL2000B, by the way, modified for 160m.

    Oh and I can't think of any other suitable valves you could fit in most of the Linears that use a pair of them mounted horizontally (unless anyone has any suggestions?) - there aren't many SB200 amps here in the UK, but lots of FL2100, FL2100B, FL2100Z, FL2000B and KW1000 amps.
     
    Last edited: May 17, 2015
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Very interesting... if the grid line opened up, the valve would melt. Cathode line, no light... must be the plate. Bad weld at the cap?
     
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    Actually no that is not what would happen.

    From experience;
    When the grid lead opens up the grid builds up a static charge and conduction stops.
    Now if you shorted the grid to the cathode Yes the tube would conduct and most likely blow a seal or suck a hole in the glass if left long enough.
     

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