Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Carl -
All the "probe" needs to be is to have a 1M resistor _at the probe
tip_, for DC measurements only. Worst case you can make a probe and
have another without the resistor for AC and Ohms measurements. The
only tricky thing about the Heath probe was that it had a method to
switch the resistor in or out at the probe point. If you have a
separate DMM, you'll probably never use the VTVM for AC or Ohms
measurements anyway!
By the way, don't fall for the "mods" circulating that explain how to
put a 1M resistor INSIDE the VTVM to "automatically" switch the resistor
in and out. The Heath (and RCA and B&K and Knight and EICO and ...)
engineers were smart enough to have done this themselves, IF that was
the "right" answer. These mods were "designed" by people who didn't
understand WHY Heath originally went to the trouble to design and build
a probe with the switch in it.
The reason to put the 1M resistor AT THE PROBE TIP was to "decouple"
that 3' test lead (antenna, variable capacitor, inductor, link couping)
from the measurement point for the _high impedance circuitry in tube
equipment_!
A little knowledge can be a dangerous thing!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
[EMAIL PROTECTED] wrote:
[EMAIL PROTECTED] writes:
You might want to keep your eyes open for one of the Heath VTVMs
Hi Garey,
And somewhere on the internet was rebuilding instructions (or have it
done) for the probes I believe I found the article somehow through the
drakelist.
Carl WD8NHK
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