On 03/20/2014 05:03 PM, Trevor Wilson wrote:
On 20/03/2014 3:16 PM, 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
**Crazy idea, Lenny:
Move yourself into the 1970s and buy yourself a digital multimeter. Most
of them operate on a 9 Volt battery. Replace the battery every year and
you'll be sweet. Even a US$20.00 meter will give you a vast improvement
in every performance parameter over your ancient POS, which is likely
well outside it's original performance specs.
Like this one:
http://au.mouser.com/ProductDetail/E...qaRLKRQ5wis%3d
One of my meters measures the usual Volts, Amps & Ohms AND light
intensity, sound pressure level, relative humidity and transistor gain.
I recall that it cost me AUS$50.00.
I have a nice collection of analogue meters (I recently acquired a
beautiful AVO 8 Mk7), but I never use them anymore.
AVO went south after the Mk IV, which is a thing of great beauty. (My
Mk IV came from the collection of a guy who also collected and restored
antique Rollses.)
Go digital. You will not be sorry.
Your garden variety DMM isn't much use above a kilohertz, though.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net