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

    Congratulations!

    You are now a member of a very non-exclusive club.

    TOM K8ERV Montrose Colo
     
  2. W1GUH

    W1GUH Ham Member QRZ Page

    'EY:

    What math? All I see is arithmetic! <-- Just bustin', of course.
     
  3. K9STH

    K9STH Ham Member QRZ Page

    The little Harbor Freight, red cased, DMMs are often on sale for as little as $1.95 and sometimes even free with a particular coupon. The measurements are usually pretty much the same as with my Fluke. A new 9-volt battery often costs more than the DMM cost! If one happens to "blow" the unit, a new 1 usually costs less than a soft drink at McDonald's!

    I have acquired a number of those units. I keep 1 in every tool box, in the glove compartment of my vehicle, in drawers where my wife keeps the bits and pieces that come with every new appliance, even on my workbenches, and so forth. If I need to make a quick measurement, I don't need to hookup one of my more expensive DMMs, and the accuracy is "good enough for government work". Of course, they are not self ranging, and one does have to be careful, especially when measuring voltage. But, since they are "throw away" if one makes a mistake, they are definitely worth what they cost!

    Glen, K9STH
     
  4. KB1WSY

    KB1WSY Ham Member QRZ Page

    I just ordered another Harbor Freight one, for the outrageous price of $7 including shipping (Amazon Prime). Unfortunately HF is a good half-hour drive away and I hate driving so I only make the trip when buying Big Stuff -- I got my original DMM there when buying a large floor-standing drill press, the meters were at the checkout counter just like candy in supermarkets. Before disposing of the old DMM, I am removing the fuse and the battery, which together are definitely worth more than the meter itself.

    I think something like the Simpson 260 8-P is definitely in my future, but as you said, it's useful to have these disposable backups....

    Apparently you can never have too many meters.
     
  5. N2EY

    N2EY XML Subscriber QRZ Page

    You are correct, sir!!

    Good point!
     
  6. N2EY

    N2EY XML Subscriber QRZ Page

    If you figure in the cost of the gasoline to drive there and back, you may have actually saved money by getting it online.

    There's also the question of "what's your time worth?"

    It's interesting how some folks (not you!) will gripe and moan and complain about shipping costs - but not thing about what it costs them to drive someplace rather than have something shipped to them.
     
  7. N2EY

    N2EY XML Subscriber QRZ Page

    Yep. Note that neither the positive nor negative output of the supply is grounded.

    That's another way to look at it.

    Me too!

    One does not really know something until and unless one can explain it to others.

    Surprising how a VTVM is fundamentally so simple yet also so complex and elegant......

    The whole thing is actually a form of bridge circuit, with the two triode sections forming two "arms" of the bridge.

    Trivia time:

    There is another type of VTVM called the "slide back" voltmeter. It is rarely seen because it is more complex to use.
     
  8. KC9UDX

    KC9UDX Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    The only use I've thought of for the Harbour Freight meters is to have 6 or 7 of them connected to something at the same time for troubleshooting. Beyond that, I'll spend the extra $5 and get an analog meter from Radio Shack. When I pull that out of the glove box after ten years it still works for voltage, without leaky dead batteries.

    Incidentally, I used to work for a guy that had a whole toolbox drawer full of those Harbour Freight meters. There were plenty of times when I found them giving wrong numbers.
     
  9. KB1WSY

    KB1WSY Ham Member QRZ Page

    Try explaining how a regenerative receiver works. Specifically, how a single tube or transistor can be a tuner, a detector and a very high-gain amplifier, all in one. In the book from which I built my receiver, it takes 12 column inches to explain what that single component does. Even then, it's mainly a conceptual explanation rather than an electronic one -- try to figure out what each part of that little detector circuit actually does, and it's fairly bewildering. I've messed around with various component values in that circuit, and this can make a big difference, but figuring out why it makes a difference (and predicting what kind of difference!) is a challenge.

    So, ironically, some of the simplest circuits in radio (which are usually the ones that were built by beginners) are also among the most complex to understand, at the component level. A TRF, despite the larger number of stages, is much easier to figure out than a regen. Even a superhet isn't that hard (one you understand the concept of heterodyning), because each stage has a defined task rather than being multipurpose.

    Yes, the word "outrageous price" was intended to carry some irony. I like traveling (if someone else is doing the piloting), but getting in the car just to go and buy something whose specs I already know in advance (i.e. no "window shopping") is just a waste of time and money. I work at home, so hobby time is pretty much stolen from work time. I'd rather be building stuff than driving to a store.

    Rather presumptuously, I've actually started doing that myself -- mainly in the Homebrewing forum over on eham, not here. Not sure why I'm doing it, because almost 100 percent of the "readers" of my explanations are experts who know much more than I do.

    I guess there are several motivations:

    (1) It helps me to clarify things in my own mind; and if I make a mistake, someone is sure to bring it to one's attention!

    (2) There is a small chance that a few of the readers will know even less than I do, and might learn something.

    (3) A general hope that by communicating enthusiasm, and facts, it will encourage homebrewing by others. I have already seen some verbal evidence of that. I know that I, for one, am greatly helped by other people's encouragement.

    A few weeks ago I even posted a primer on vacuum tube theory, largely in my own words! The gall!

    Edited to add: concerning, "one does not really know something until and unless one can explain it to others." I think that sentence carries significance as concerns our ham radio license tests. I'm not one of those people who constantly complains about the current tests.

    However, IMO, preparation for a multiple-choice test (which has been the format for many decades now) does almost nothing to develop the sort of expository reasoning that is necessary for an essay-type response, or for the kind of reasoning required in complex problem-solving. Just sayin'.

    So, passing the ham test is really only the beginning (in the old days, it often came at the end of the "learning and building" process rather than the beginning, as Jim has pointed out elsewhere).
     
    Last edited: Sep 18, 2014
  10. KB1WSY

    KB1WSY Ham Member QRZ Page

    Getting back to the thread topic.

    101_Heath.jpg 102_ME26DU.jpg 103_Knight.JPG
    104_RCA.JPG 105_HP.JPG VTVM_1.jpg

    (Heathkit, Military, Knight, RCA, HP, my Eico.)

    Not much to distinguish between them except that some have the function switch on the left, some on the right.

    Except that mine's the prettiest and the bestest, of course.
     
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