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Discussion in 'General Technical Questions and Answers' started by W8ETD, Aug 14, 2021.

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  1. W8ETD

    W8ETD Ham Member QRZ Page

    Can you identify this tube?

    Attached Files:

  2. NT6D

    NT6D Ham Member QRZ Page

    Most likely Eimac 3CPX1500A7.
  3. KA5IPF

    KA5IPF Ham Member QRZ Page

    Look for an etched serial number and contact EIMAC.
  4. KA0GKT

    KA0GKT Ham Member QRZ Page

    The difference between a 3CPX1500A7 and a 3CX1500A7 is that the CPX version is meant for pulse operation in Plasma generator systems. I haven't ever used a CPX in place of a CX, but looking at the specifications, would guess that a 3CPX1500A7 would work as a substitute for a 3CX1500A7, but not visa versa. there are differences between tubes meant for pulse operation and tubes used for linear operation, one is that a tube in pulse operation will not tolerate a "Dirty" vacuum.
  5. KP4SX

    KP4SX Premium Subscriber QRZ Page

    So which do you think it is?
  6. VE7DQ

    VE7DQ Ham Member QRZ Page

    Likely a CPX, 'cuz the ceramic insulator appears larger than on the CX for higher voltage standoff.
  7. KA0GKT

    KA0GKT Ham Member QRZ Page

    I tend to agree, also the external anode appears to have run somewhat warm. The industrial tubes often have been operated at the very edge of CCS parameters and the anodes get warmer than they would in ICAS service. Also, replacing tubes in plasma sputtering or dielectric heating equipment is considered CODB (Cost of Doing Business), if a cooling fan isn't working or a filter is clogged, it costs less to replace an overheated tube than to shut down production, so tubes get cooked. I wouldn't be all that surprised if that tube didn't meet specs if you were to test it...or have Eimac test it.

    Because the CPX version is a physically taller tube, some modification to the amplifier may be needed to use it instead of the CX. If you're buying new, the CPX is more expensive, a Chinese 3cx1500a7 tube can be as little as $600.00, an honest-to-goodness Eimac will run you twice to three times that figure (Perhaps more depending upon your dealer) It's been a while since I purchased one. I don't have any hollow state FM broadcast transmitters any more, and the tubes in the DTV transmitter are Inductive Output Tubes and are so large that they require a chain hoist to lift them out of the carriage to be shipped for rebuild.
  8. NT6D

    NT6D Ham Member QRZ Page

    3CPX 15000A7 has taller ceramic wall due to the higher plate voltage and so does tube in the OP.
    Here is a pic of both tubs side by side. 3CX1500A7 is on the left and CPX is on the right.


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