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Multiple identical-looking VTVM's.

Discussion in '"Boat Anchor" & Classic Equipment' started by W1GUH, Sep 16, 2014.

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  1. K8ERV

    K8ERV QRZ Member QRZ Page

    Not it. I just checked Google images but no joy. I could have the model wrong. Was a true zero-center meter.

    TOM K8ERV Montrose Colo
     
  2. KB1WSY

    KB1WSY Ham Member QRZ Page

    So many times, people have reminded me that the selenium jobs can explode and give off poisonous fumes.

    I've become so intrigued that I'm even considering removing the selenium rectifier, putting it on a small workbench in the open air, and feeding it with a steadily increasing load until it explodes! (From a distance, with a long wire, and wearing eye protection.)

    Hihi.
     
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    Don't do that......
    They are under certain circumstances self healing.
     
  4. N2EY

    N2EY XML Subscriber QRZ Page

    "can" doesn't mean "will".

    However, you bring up an important point: Fusing.

    In the bad old days, it was common for things like VTVMs not to be fused. I think they would pass UL requirements if they did not burst into flame if a filter cap or selenium rect let go. If the failure took out the power transformer, that was OK, as long as no fire resulted.

    Today, filter caps and silicon rectifiers are low-cost, but a replacement power transformer is practically unobtanium. So a fuse is a good idea.
     
  5. KB1WSY

    KB1WSY Ham Member QRZ Page

    Will do. In the AC line, not in the B+ line, right?
     
  6. N2EY

    N2EY XML Subscriber QRZ Page

    Right. You want to protect the entire instrument.

    btw, I have seleniums which are decades old and still working fine.
     
  7. K8ERV

    K8ERV QRZ Member QRZ Page

    I love the smell of selenium in the morning. (Sorry Robert).

    TOM K8ERV Montrose Colo
     
  8. WN6U

    WN6U Subscriber QRZ Page



    Good luck Tom, sometimes the value of antiques drops. :(
     
  9. KB1WSY

    KB1WSY Ham Member QRZ Page

    Yeah, I know what you mean, why mess with something that's working fine? Which mainly explains why I haven't replaced it yet. (Edited to add: mind you, I have several other pieces of small Eico test gear that, I suspect, also have seleniums. So, the lottery has started!)

    I read somewhere that a factory (in India?) is still manufacturing selenium rectifiers, for use as drop-in replacements in old equipment. Not sure what the point is: silicon diodes are so cheap, and so are resistors. I suppose it's the labor involved in fitting the silicon to the application that is costly.
     
  10. K8ERV

    K8ERV QRZ Member QRZ Page

    Looks like my memory failed. All the EV-10 pix show a normal left zero meter. So maybe I had to set the needle to center
    with the adjustment control. I probably just left it there.

    TOM K8ERV Montrose Colo
     
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