3-400z to 3-500z

Discussion in 'Amateur Radio Amplifiers' started by W4WTS, May 14, 2019.

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  1. W4WTS

    W4WTS Premium Subscriber QRZ Page

    My Hunter bandit 3000c uses a couple of 3-400z....I've read that a few people have replaced them with 3-500z's.....

    Anyone have any experience with this?

    Comments appreciated.
  2. N2EY

    N2EY XML Subscriber QRZ Page

    The two are very similar.....but there's one issue to watch for:

    The 3-500Z is 6 inches high. The 3-400Z is only 5-1/4 inches high. That extra 3/4 inch can be an issue.....or not.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    One other smaller issue, assuming the tubes physically fit the space available:

    3-400Zs were "zero bias," and even at 3000-3500V anode voltage really didn't need introduction of operating bias to limit idling current.

    3-500Zs aren't, and at plate voltages above about 2500V can draw quite a lot of idling current (ZSAC), so are almost always used with a source of bias introduced to keep that down to something reasonable. Most use in the range of 5->8Vdc bias, either as a negative voltage to the grids or a positive voltage to the cathodes. No use burning up the tubes with a lot of needless dissipation.
  4. WA8UEG

    WA8UEG XML Subscriber QRZ Page

    Definitely going to need bias.

    Some amps included bias disconnected so you could use either. As someone else mentioned you need to check and make sure there is enough height to accept the taller 3-500.

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