On 10/06/2018 10:06 PM, Scott Dorsey wrote:
In article , Trevor wrote:
On 10/06/2018 12:48 PM, Mike Rivers wrote:
On 6/9/2018 6:29 PM, Phil Allison wrote:
In the 1950s and 60s, the standard bench instrument for professional
techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html
I have one of those on my workbench, and it still works.
The AVO meters were the most common in places I worked. Still have my
AVO model 8. If you don't fry them, no reason they won't outlast the user.
I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier
You could say that about digital CRO's Vs analog ones too. Spent a lot
of time adjusting CRO's before you'd even attempt to use it.
I do keep a Simpson 260 on my bench and I use it often. It lets you see
trends, count capacitor discharge curves, and so forth. The comparatively
low impedance means it won't get false measurements through leakage. But
it's just a coil of wire inside a magnet, there's no active electronics in
there.
To be fair the AVO's were not VTVM's, just a meter, multipliers and
shunts. But you did need a VTVM/SSVOM or CRO when loading was a problem.
Not something people often worry about these days with modern digital
multi-meters, even when they should. 10Mohm is a lot better than
20kohm/volt in most cases, but if you are working with Megohm plus
impedances, you still need to know about loading. Amazing how many
people get caught out still.
Trevor.