Viking Adventurer meter shunts change

Discussion in '"Boat Anchor" & Classic Equipment' started by W8AAZ, Dec 5, 2018.

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  1. W8AAZ

    W8AAZ Ham Member QRZ Page

    Heads up for anyone restoring or repairing one of these old Adventurer CW transmitters. I assume people with issues might find this in a google search. The meter shunt resistor values were changed during the production run. My TX is serial 81000 range and the manual that came with it from previous owner that worked on it is for a late 84000 range In the earlier ones, the grid shunt R4 is 1K and the later value 200 Ohms. The earlier plate meter shunt R5/6 is 50 Ohms, two 100's in parallel. The later production is R5, 10 ohms. I found out by accident as the previous owner did some repairs and put the 10 ohm shunt in, and I could not get a correct plate current reading, even though the power output was nominal. Apparently the older meter was less sensitive. And conversely, if you installed the older values into a later radio, it might peg or damage the meter. The manual I have lists the later low value resistors in the parts list and the large schematic. The older values showed on the small schematic on the glossy advert. handbill page in the front.
     
    KD2ACO likes this.
  2. N2EY

    N2EY Premium Subscriber QRZ Page

    Good info - thanks!

    Also:

    It's a good idea to verify the actual current readings in old rigs, due to resistor drift and similar effects. This can be easily done with a multimeter of known accuracy, a battery, a variable resistor and some clip leads.

    What you do is to put the meter of known accuracy in series with the metering circuit of the rig, and power the whole mess with the variable resistor and battery. That way you can be sure that when the meter in the rig says 100 mA plate current, it really is 100 mA.

    This also permits using common resistors in metering circuits rather than having to use precision units.

    73 de Jim, N2EY
     
    Last edited: Dec 5, 2018
    KD2ACO likes this.

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