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HW-16 meter full scale plate reading

Discussion in '"Boat Anchor" & Classic Equipment' started by K1OA, Mar 13, 2010.

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  1. K1OA

    K1OA Ham Member QRZ Page

    When I key my HW-16 with the meter in PLATE mode
    I'm seeing a full scale deflection, on all 3 bands, pins
    the meter. In REL PWR mode, on 40 and 15 the
    deflection seems reasonable, but on 80 it too is almost
    full scale.

    I've replaced the meter, as well as the transmit oscillator,
    driver and final tubes.

    Output power is good and everyone I work says the CW
    tone and stability are excellent.

    There aren't many components in the path to the meter but
    could one of those be bad? Could this be a final tube
    neutralization problem? The only adjustments I've made
    are tweaking the driver coils to get more output power,
    I haven't performed the neutralization procedure yet,

    tnx and 73,
    Scott
     
  2. WA7KKP

    WA7KKP Ham Member QRZ Page

    bad meter shunt . . .

    Look in the schematic -- there should be a resistor in the cathode lead that has a pair of wires going to the meter switch. Odds are that it has aged, and increased in resistance, which would indicate (falesly) high plate current.

    It was common practice to use a meter as a voltmeter, and measure the voltage drop (proportional to current through) a resistor. Instead of a more expensive shunt, one could use off the shelf resistors to do the job.

    Borrow a good DVM, and check the value against the parts list and schematic. If this checks okay, maybe there is a multiplier resistor in series with the meter that has dropped in value -- this could also explain the sensitivity issue on FWD POWER as well . . .

    Easy to fix . . . as most Heathkits were. That was their best attribute. Hardly anyone fixes their own radios these days . . . (sniff sniff).

    Gary WA7KKP
     
  3. K1OA

    K1OA Ham Member QRZ Page

    Hi Gary - That was part of the problem, R15 was twice as high
    as it should be, 30 ohms vs 15 ohms. Replacing that stopped
    the meter from full deflection in PLATE mode.

    But the meter was still off by about 50 mA using the
    voltage measurement across R15 as compared to the
    meter reading. I got back about 25 mA or so by adjusting
    the meter needle to sit as far low as it can go.

    Not sure what else to look at, this might just be as good
    as this meter gets.

    thanks,
    Scott
     
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