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Amp Supply LK500-ZC

Discussion in 'Amateur Radio Amplifiers' started by AB2NI, Oct 11, 2020.

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  1. AB2NI

    AB2NI Ham Member QRZ Page

    I am looking at purchasing an Amp Supply LK-500ZC. Ham that has it for sale got it from an estate and has not tested it yet as there is a lot of equipment. Price is reasonable (all I will say).
    I have searched this amp and not come up with a lot on the ZC series, so I am looking for advice and experience others have had. Has an original pair of 3-500Zs. I have a few photos from the seller. Looks rewired? One of the coils looks like it got warm? Looks to have the 10M mod.


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  2. W1QJ

    W1QJ Ham Member QRZ Page

    Nice amp, built with generic parts, easy to repair. The ZC model has the ALO board which really is a waste. If something goes wrong with it just remove and junk it. The fan on high speed sounds like a jet engine. Will do 1300 watts . Has a Peter Dahl transformer. The photo shows that one has 10 meters. I don’t see any rewriting. Everything I see looks factory. It’s good the good style band switch. They all lack sufficient inductance on 160 meters.
    AB2NI likes this.
  3. VE2GCE

    VE2GCE Ham Member QRZ Page

    It is a well designed amplifier, no regrets with my LK500ZC.

    There is some upgrades that I am aware according to the service report of my amp gave the previous owner gave me:
    - Upgrade bandswitch
    - Replacement of front panel switches
    - Replacement of fixed load capacitors for 160 meters
    AB2NI likes this.
  4. AB2NI

    AB2NI Ham Member QRZ Page

    What do I need to do to modify & update 160M ?
  5. W1QJ

    W1QJ Ham Member QRZ Page

    The load cap always goes full mesh as if you need more load C. I’ve beat myself up adding hundreds of picofarads of additional padding and still the same result. Some other amps exhibit the same problem and I’ve trying adding more padding and still no help. The bottom line is there is a lack of sufficient inductance and there is no substitute for that unless more inductance is added.
    AB2NI likes this.
  6. AA1XV

    AA1XV Ham Member QRZ Page

    Your pictures don't show the QSK board (it was an option on some), or the P.S. board.
    My upgrades:
    1- Replace the plate choke with an Ameritron ($20). 160M will tune better and better output.
    2- Soft start from Harbach (the power switch will thank you).
    3- Replace the fan with a good quality all metal one. (PABS)
    4- Replace the P.S. board with the kit from Harbach, (if you have toe original, it is a must after 34 years).
    5- Add a plate glitch resistor. Do not add a fuse in series with it.
    6- Do not replace the band switch. Yours has the better one.
    I cannot think of a better 2 x 3-500z type of amplifier, present or past after these upgrades. No, the AL82 pushes too much the envelope.
    AB2NI likes this.
  7. AB2NI

    AB2NI Ham Member QRZ Page

    Regarding the plate choke recommendation, are you referring to the one this SB-220 was modified with?

    The P.S. Cap Kit from Harbach is ordered. Confirmed, no QSK board.

    I appreciate your guidance.

    Last edited: Oct 18, 2020
  8. AA1XV

    AA1XV Ham Member QRZ Page

    AB2NI likes this.
  9. VE2GCE

    VE2GCE Ham Member QRZ Page

    Could you give me the details of the plate glitch resistor ? My amplifier does not have this modification.
    AB2NI likes this.
  10. AB2NI

    AB2NI Ham Member QRZ Page

    The plate choke is ordered from Ameritron as RF Parts does not have any in stock. Two dollars less and the S/H was also a bit less.
    Regarding the plate glitch resistor, it goes inbetween the choke and the final connection to the plate? VE2GCE would also like to confirm its position. Then again, in a series circuit, the location of a fusible resistor does not matter. I'll add one to my SB-220 also. VE2GCE Harbach sells them in packages of 5.

    Don't worry, I'll be back with more dumb* questions. * = newbie, needs help, I don't know everything, etc.


    VE2GCE likes this.

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