Transmitter tubes of recent production are prone to easily break, aren't they?

Discussion in 'Amateur Radio Amplifiers' started by JL1DCA, Apr 28, 2017.

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  1. JL1DCA

    JL1DCA Premium Subscriber QRZ Page

    Hello, folks.

    I've got a pair of 572Bs in my linear amp ruined by a contenious carrier transmission at its maximum output.

    I had though they were robust enough to stand as much stress as that.

    What's your opinion?

    Thanks, in advance.

    JL1DCA Taihei Suzuki
     
    Last edited: Apr 28, 2017
  2. KM3F

    KM3F Ham Member QRZ Page

    All the small tube amps are not robust enough the run like that.
    Look at the plate voltage and plate current.
    Calculate the DC power input you see.
    Then check the max total tube plate dissipation.
    You will find it's several; times over the limit the tubes are good for on constant carrier service.
    For SSB mode its the low average current duty cycle of speech that permits the peak powers to be attained that cannot be done with constant carrier operation.
    Said another way, if you carry a heavy sack a short distance ok, then carry it a long distance until you cannot go any farther, it takes you down. Carry the same sack multiple short distances, you can take it a long ways without failing under the load of weight.
    It's the average energy expended for the whole time vs distance interval.
    Where have you been for all this?
    Good luck.
     
    Last edited: Apr 28, 2017
    N5WVR and KD2ACO like this.
  3. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    What amplifier are the 572's in? With good cooling, I think you can expect about 150 watts continuous power, maybe a little more or less depending on the amp, but especially the quality of cooling.

    For example, if you run AM mode, tune the amp for 600 watts (or full power) but turn the carrier to 125-150 watts in the power setting stage (after tuning the amp for max power). RTTY? 125-175 (200?) watts or so... Dull red plates are OK, bright red is a meltdown in minutes.

    Hopefully, you can see the tubes while in TX. The color of the tube's plates will let you know how they are feeling! :)

    edit:
    I installed some brand new Taylor 572b's in my SB-200 to see how the new tubes are doing, and they work just like my still good Cetrons from 1977 production. We will see how they last, but they are very nice.
     
    Last edited: Apr 28, 2017
  4. JL1DCA

    JL1DCA Premium Subscriber QRZ Page

    Thank you for the info, everyone.

    I had run them certainly longer than the period of of time Yaesu warns not to exceed when FL-2100z is in its full operation.

    I'll have to import from RF PARTS another pair of them and be more considerate not to abuse them.

    Suzuki JL1DCA
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Do you have pictures of the tubes ?

    Did the glass melt ?

    That is fun to see, But it is like smoking the tires on your Hotrod, It gets expensive.
     
  6. JL1DCA

    JL1DCA Premium Subscriber QRZ Page

    I haven't opened the linear to see the tubes yet, so I can't tell its outward appearance.
    Ip is, after the event, about a half of what it should be .
    I could hear once a noise from inside the gear as if a tube was sparking inside when tuning the matching after accident.
    I'll put them out later today to see if the shape of the glass is altered.

    JL1DCA Taihei Dan Suzuki
     
    Last edited: Apr 29, 2017
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What is the amplifier?

    Heath and Yaesu (and probably others) often used 572Bs laying on their sides in normal operation (horizontally installed) which does put additional stresses on the tubes.

    Ameritron in the AL-572 uses them vertically installed, which doesn't impose these stresses.

    I've always th0ught when using these tubes horizontally it would be a great idea to add a supporting system to "hold up" the anode seal end of the tubes, placing less strain on the base pin seals. But there would remain the issue of hot elements inside the tube sagging from gravity, and superheating them would seem to make this issue worse.
     
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I think he has an FL-2100z.
    In the interest of good international ham relations, I've got my old pair of Cetrons in my carry on. Will trade a sushi dinner for them!
     
    AH7I likes this.
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    FL-2100's have several design drawbacks including a silly biasing scheme and two tiny underpowered fans that don't do much.

    But...they can be improved! The power supply is good.
     
    AF6LJ likes this.
  10. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I haven't run into one. Can you judge the plate color (peek inside) while it's running?
     

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