US Navy Tube tester: Bad meter question

Discussion in '"Boat Anchor" & Classic Equipment' started by KN4SMF, May 28, 2021.

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  1. KN4SMF

    KN4SMF Ham Member QRZ Page

    I have consistently proven to myself that I can go into a weekend with 2 projects to finish, with a third lined up for another weekend soon. My rule is that 3 projects must be completed within a 2 month period before I buy or trade for any more. At Christmas, I intend to have 7 new pieces of vintage gear in proper correct working condition, and that those pieces must be dependably useful on an ongoing basis. That's the rule. Or out it goes to a better man that can do it.
    I have here my US Navy tube tester. I have determined the meter is bad. I want this thing working correctly, but don't have a clue as to where to procure a replacement meter or a meter movement to adapt in to the meter case. Milliamps, Microamps, or whatever. As I understand it, most meters will be one or the other. If anybody has a clue as to where to start, I would be grateful. the rest of the machine has a very strong "electronic smell" with a hint of a burned odor, but everything looks undamaged. As far as that goes, it looks like the typical capacitor and resistor job that all these old pieces of gear get in a proper refurbishment. Thank you.

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  2. W3SLK

    W3SLK Ham Member QRZ Page

    I would suggest possibly Fair Radio or Surplus Parts of Nebraska or maybe even Murphy out in CA. I think I would actually try to talk to the guy there at Fair Radio. They may not have something in their catalogue but might have something on the shelf.
  3. SM0AOM

    SM0AOM Ham Member QRZ Page

    Looking at the general arrangement of the meter capacity scales, I have reason to believe that the meter is a 50 or 100 microamperes full scale deflection moving-coil meter.

    This also comes out of the equivalent circuit of the TV-4 found on a British forum:


    The meter is shunted by an 88 ohm resistor which implies that the meter is more sensitive that the usual 1 mA variant that usually has an internal resistance in the order of 80 ohms.

    However, the proper way to find out is to
    connect a multimeter to the circuit in place of the meter and then short the capacitor test leads together in the Cx10 test position.

    The multimeter should then indicate the full scale value of the meter.

    It must however first be determined if the rest of the circuit is intact so no short-circuits will damage the multimeter.

  4. KE5MC

    KE5MC Premium Subscriber QRZ Page

    In the meter picture in the lower left corner of the glass I see the top of a line of print. I have seen that on other meters identifying their full scale deflection current. If that is what it is then it narrows the replacement field. If the meter is really bad, disassembly will have to happen when you find a replacement. If done now you might identify an internal mechanical issue you can fix depending on the symptoms you have to work with now.
    I never ran across that test set in my seafaring days. I had access to a Hickok (?) tube tester with a 4 inch stack of plastic punch cards. Insert correct card, push test and done.
    Wish I could help with finding replacement. Look like an interesting piece of kit.
    Good Luck,
    73, Mike KE5MC
  5. KN4SMF

    KN4SMF Ham Member QRZ Page

    I'm a Hickok fan. Never heard of that tube tester. Wish I knew what it was so I could get a picture of it. Sounds neato. thanks.
  6. KN4SMF

    KN4SMF Ham Member QRZ Page

    That line of type in the corner you mention simply says "Model 685".
  7. KJ4YEV

    KJ4YEV Premium Subscriber QRZ Page

    It might be worth opening up the meter to check it's internals.

    If it's like Hickok testers, there is an internal series resistor that sometimes opens up. It's a precision wirewound, on a spool.

    I don't remember the resistance, but I fixed mine by using a series combination of three 2% resistors, which got me very close.
  8. KE5MC

    KE5MC Premium Subscriber QRZ Page

    Found link on ebay using the following search term.

    US Navy USM-118A Cardmatic Tube Tester
  9. KN4SMF

    KN4SMF Ham Member QRZ Page

    Pulling this project back up tho the work table and testing this meter movement once again, it definitely does not work. No reaction at all. And no change in the "shake test" by shorting the terminals. The meter is dead. What is this part in the photo? Could it be the culprit?

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  10. W9GB

    W9GB Ham Member QRZ Page

    It may be a calibration resistor, in series with the meter.

    Ron Taylor posted Weston TV-4/AU restoration questions on Antique Radios (July 2017)

    Service magazine, March 1941
    Weston 777 (design that TV-4/AU likely based upon) found on Pages 16, 22
    Ed Engelken (Arizona AM Net) pulled his TV-7A meter.
    The TV-7A meter was manufactured by the Roller-Smith Company of Bethelehm, PA.
    Both the full-scale sensitivity (200 microamps) and resistance (2365 ohms) were printed on the meter scale.

    Dieter Wächter (Germany) restored and repaired a TV-7 tube tester, photographing and describing every individual restoration step — even rebuilding the meter.
    This web page is for private, non-commercial usage.
    Likely beyond the patience or skill set of many — it does demonstrate what is possible.
    Last edited: Jun 14, 2021
    KD0CAC likes this.

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