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WTB VTVM

C

Cydrome Leader

Jan 1, 1970
0
tm said:
Good point. However you will pay an accuracy premium on the DC and Ohm
ranges. Most VTVMs will only give 3% FS vs <1% with even the cheap DVMs.

Cheapo meters seem to do DC stuff OK, and I've never dusted off the Leader
meter for stuff like that.

It's really nice for AC though. There's nothing quite like the dampened
needle movement for stuff like an audio signal. No number of constantly
jittering digits on a DMM can compete.
 
C

Cydrome Leader

Jan 1, 1970
0
Mike Cook said:
Would you explain please? Is the FET input impedance so much higher that it
loads less than even a high-quality DMM?

yes.

I can't explain why this is but a call to HP and a check of the schematics
do show an AC input impedance of 1.7M (or something else bizarrely low)
for some AC ranges on a HP44301 bench meter.

There's also this problem of leaking voltage back out onto the test
probes:

http://www.home.agilent.com/owc_discussions/thread.jspa?messageID=99671

It's not to say the 34401 sucks- it's a really nice meter, but simply
being an expensive piece of test equipment from a trusted brand doesn't
always mean you get infinite accurracy with infinite input impedance and
an superconducing burden load for current ranges.

There's no way this is the only piece of test equipment with weird quirks
either.

you can run in circles over stuff like this if you just assume it's not
your test equipment.

I had an incident with a failed diode in Simpson AC panel meter once. How
often do meters half burn out giving you wacked out readings? Apparently
it happens.
 
C

Cydrome Leader

Jan 1, 1970
0
Jamie said:
My Fluke 289 will measure correctly with the 40k probe doing
AC or DC. So won't a couple of older flukes I have.

Those particular probes (I think Pomona had some too) require a fixed
input impedance on your meter, or the divider math falls apart. It seems
Fluke has no problem with this, although I've not yet tested the probe
with my latest Fluke meter. THere really isn't warning about this on those
probes, although it says so in the manual, but who has those laying
around?

for microwave ovens, when they were worth fixing, a yoke tested was easier
and more certain for HV measurements.
THe only problem with AC and a HV-probe is you need to keep
the frequency down, otherwise, the small amount of cap present
on the input of the meter is going to attenuate it some.

I have no way to test outside of 60Hz, but I am curious about how far they
drift off.
 
C

Cydrome Leader

Jan 1, 1970
0
The little HF LCD display multimeters seem to have pretty high input
impedance, but I've never actually tried to measure it. Certainly
much higher than the old Simpson multimeters.

they still make those simpson meters. I want to know who buys them, and
what for.
 
C

Cydrome Leader

Jan 1, 1970
0
tm said:
Yes, that is why I sometimes wrap a resistor on the tip of the probe to make
the measurement.
Of course with a scope probe, that's not a problem.

Still, there is much one can do with a Harbor freight $10 DMM.

I wonder, if you could only have one instrument, what would you choose? If
cost were the main consideration?

I think any generation of handheld fluke meter would keep me happy for
general troubleshooting.

the cheapiest working meter I have is some pocket sized Wavetek DMM. It
works fine and has a surprisingly good, high contrast large LCD.

I still have some Radio Shack analog meters, but they have burned out
ranges which should be easy enough to fix.
 
W

William Sommerwerck

Jan 1, 1970
0
They still make those Simpson meters. I want
to know who buys them, and what for.

They require no batteries (except for the ohmeter), and it's easy to follow
rising and falling readings.
 
C

Cydrome Leader

Jan 1, 1970
0
Michael A. Terrell said:
Military & industrial customers who have millions of pounds of
equipment where all readings in the manuals were taken with Simpson
meters.

that's a good enough answer.

I saw a simpson meter on a shelf at Argonne national lab recently and at
first though, wow, that's old, but changed that thought to wow, pretty new
stuff there for a government run lab.
 
I can understand the desire for an analog meter. These days I swear there must be more parts in a TV to keep it from working than to make it work. Shutdown, why ? There could be bunch of reasons. They are too cheap to really build current detectors into them so they assume when a voltage source is out or low there is an overload on it. So the sumbitch shutsdowwn before your DMM can measure any voltages. A VTVM will at least show you the neelde moving. On my DMM sometimes it's hard to see the "mV" indicator, and I think it is a bit slow even as autorangers go. Also when you see that needle movereally fast you know to get off that test poinr=t and change the range NOW. Not after a cheap microprocessor finally notices that it is burning in hell.

I also have some of those cheapo DVMs from Harbor freight. We got them for quite a bit less than ten bucks, in fact I think some of them were four bucks. Literally cheaper than the nine volt battery they use ! What's more youcna always get a free one. We had one that wouldn't zero so we called themand they send out a new one. They said don't bother sending the old one back lol. Wwell it was good for another battery anyway. However those little things are plenty good for almost any general servicing.

Now when you are aligning an IF strip, it's easy to see why the VTVM might be prefered. I now usually use a scope but then I don't align radio IFs anymore anyway. In fact I don't align any IFs.

Now to the OP, remember the OP ? I happen to have a non working Heathkit IM-28 (I think it's a 28) that doesn't work. The meter movement seems to be good, but the zero pot shaft is broken. I don't know if it will zero or not,but that's the circuit. The meter is fine. I'll sell it for twenty bucks. that''s actually giving it away, UPS wouldd probably be seven bucks, and ofcourse I have to find a box and all that, package it up etc.

If I am not mistaken, my Father built that. I am not sure and I am also notmuch of a sentimentalist. I just don't like to see things go in the landfill.

Also, I have a neat thing for your PCs if you want. Someone mentioned audio? This is a nice little analog looking meter that monitors the sound levelin your PC. It is chiefly used for hardware ripping, using the PC as an audio recorder of to set the levels for online streaming like you can do on Paltalk.

I got it from an ex soundman for the Beatles. He didn't write it, a guy named Chapman wrote it.

https://dl.dropbox.com/u/29948706/VUMeter.exe
 

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