DIYbanter - View Single Post

Trevor Wilson

On 22/03/2014 6:12 AM, wrote:
On Thursday, March 20, 2014 12:16:03 AM UTC-4,
wrote:
I found this circuit somewhere, (I can't remember) to replace the
1.50 volt battery in a VTVM. I have an RCA WV98C Senior Voltohmyst
VTVM that is in perfect condition but doesn't get used very often.
This battery retrofit circuit takes power from the 6.30 volt
filament transformer and is built around an LM317. With a trim pot
you set it for 1.55 volts and you never have to change a battery
again. It also needs to occupy an area no larger than the battery
presently does.

As much as I like keeping things original, I'm worried that the
battery is going to leak and rot the inside of the unit. I was
going to build the circuit but it occurred to me that I should
probably be concerned about the current that the LM317 will be
dissipating when the meter is used on the low ohms range. Does
anyone have a feel for the size that an adequate sized heat sink
should be in order to handle this? Thanks, Lenny

Besides the things I've already mentioned regarding digital vs.
analog, I've tried checking transistors and diodes with a digital,
and I suppose that you can do it but perhaps it's because I've been
doing this all my life with something like a 260, trying to do this
with a digital drives me nuts.

**Almost every modern digital meter I've ever seen has a diode test
function. It's easy to use and is often conveniently labelled with a
diode symbol.

And Trevor you asked how you insulted
me. You referred to my meter as a "piece of ****".

**So, not insulted you, so much as called your meter a POS? You have
pretty thin skin, Lenny. I'm pretty certain that if someone referred to
my AVO 8 Mk7 as a POS, I would not be overly concerned. Nor my Fluke 85,
or anything else I own. It's just stuff. If someone called me a liar, or
an idiot, or some other derogatory term, then I would be insulted.

You've never used
it nor have you ever seen it. So where the hell did that come from?

**I've owned VTVMs of the same vintage (in fact, I think I still have
one stored away somewhere). I still own a FETVOM I built (Heathkit) way
back. I never use it, because it is a POS. It was fine when I built it,
but time has moved on and so have I. It's a collector's (barely) piece
only. Same as my AVO 8, my Simpson 260, my Philips PM2403 (now THERE is
one seriously impressive FETVOM) or my General Radio 1564A (the most
beautifully constructed piece in my collection). They're all way past
being truly useful. But I like having them around. All the batteries
have been removed, of course.

You may have your own opinions but there was no reason for that
comment. Lenny

**Sure there was. You're trying to re-invent the wheel. If you want to
keep your VTVM for sentimental/collector purposes, then it's not an
issue. If you want to use it for day-to-day purposes, there are much
better choices available.

--
Trevor Wilson www.rageaudio.com.au