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Acom 1500 - 4cx1000 to 4cx1500

Discussion in 'Amateur Radio Amplifiers' started by KC4M, Apr 19, 2021.

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  1. KC4M

    KC4M XML Subscriber QRZ Page

    I ran a query with variations of the titled words, but came up with no previous threads. Consequently, I'm coming to the well of knowledge. ;)

    I have an Acom 1500 amplifier, which uses the 4cx1000 ceramic tetrode. Is it possible to swap it out with the 4cx1500?

    Both seem to have some similar specs, and I'm having trouble finding a 4cx1000 tube that's not some burned-up thing or a Chinese piece of junk. I seem to run across more of the 4cx1500 tubes on the market.

    If it is possible to do a swap, do you have an idea of what else needs to be changed? I can't image that it would be a simple matter of just plug-n-play, although that would be nice. Plus, would there be additional benefits to running the 1500 over the 1000, other than availability?

    Any direction is appreciated!!! :)
  2. KR9Q

    KR9Q Premium Subscriber QRZ Page

    I have a NOS Eimac 4cx1000a. I broke the seal on the box. Email me if you're interested.
    K4YNZ and KC4M like this.
  3. K7GQ

    K7GQ Subscriber QRZ Page

    You might drop a line to Val at Acom Support -- I'm pretty sure I read that the ACOM amps are somewhat designed around the characteristics of the Chinese tubes.
    KC4M likes this.
  4. N8CBX

    N8CBX Ham Member QRZ Page

    The 1500B will output less power than the 1000A. The 1500B was designed with emphasis on linearity as requested by Harris. I don't see any conflicts substituting the 1000A with the 1500B
    Jan N8CBX (I build an amp using the 4CX1500B)
    KC4M likes this.
  5. K7JQ

    K7JQ Ham Member QRZ Page

    Most likely the bias adjustment would be different, and the TRI tuning would have to be re-calibrated. From what I've also been told by Acom and Array Solutions, the amp was designed around the characteristics of the specific Chinese tube manufacturer they use. When I had the A1500, I replaced the original Chinese tube with a NOS Eimac, and the TRI tuning calibration was thrown considerably off, resulting in screen current problems that triggered the protection circuits.

    Bob K7JQ
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  6. W1QJ

    W1QJ Ham Member QRZ Page

  7. WL7PM

    WL7PM Ham Member QRZ Page

    " Was Val consulted, and did he offer or furnish instruction in recalibrating the TRI to function correctly with the EIMAC tube ?
    .. My communication with him implied that the Eimac tube would function perfectly, and in fact be preferential if cost were no object, a bias adjustment only being required.
    K4YNZ likes this.
  8. K7JQ

    K7JQ Ham Member QRZ Page

    Yes, there are instructions to calibrate the TRI, but it requires a scope (I don't have one) and procedures that I didn't want to tackle. The NOS Eimac 4CX1000A replacement did function properly, but I had to tune the amp based on the screen current reading, not just centering the TRI "V". I can't comment on using a 4CX1500B replacement.

    I sold the amp (revealing the tuning difference to the buyer), and purchased the Acom 1200S.

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