Amp Supply Co. question

Discussion in 'Amateur Radio Amplifiers' started by KE0OHO, Oct 31, 2019.

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  1. KE0OHO

    KE0OHO Ham Member QRZ Page

    I bought a used LK500A linear amp. The amp is stock in all ways. It works fine throwing 1500ssb effortlessly. Hears my question. It uses a pair of 3-500z tubes. The plate voltage shows 2000 volts. The manual says it should show about 3000vdc like most linears. Should I update the power supply to attempt the only thing I know that would cause the low plate voltage? Or run it as is. I get excellent reception reports and if it were not for the low plate voltage I would not be asking you experts for opinions. Tubes are stock, lot of hours but no abuse shown on them. I think the amp was made in mid '80s. One owner, mint condition but it has many hours on it because the fan is worn out and very noisy. Thanks
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If it produces 1500W output power, the plate voltage can't be 2000V.

    I strongly suspect this is a "metering error" caused by the multiplier resistors in series with the meter. If they drift high in value, the indicated voltage will be lower than it really is.

    That's a common occurrence.
    WG7X, K0UO and AD5HR like this.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    Yup it’s the series metering resistors. They should be replaced.
    KU3X and K0UO like this.
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Yup, yup. Maybe look into replacing the fan too while you’re in there.
    Last edited: Nov 1, 2019
    K2XT likes this.
  5. KE0OHO

    KE0OHO Ham Member QRZ Page

    All Righty, thanks to you hams for the invaluable advise.
  6. N8FVJ

    N8FVJ Ham Member QRZ Page

    BTW- a great amp. Enjoy.
  7. KE0OHO

    KE0OHO Ham Member QRZ Page

    Ended up that the power was soft but running 2kv it worked fine up most of a 1000w meter. After a new power supply it was measured at the shop at 1000watts CW and 1800 PEP on a bird 43 with origional US tubes. Not bad at all.
    KD2ACO likes this.

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