Re: Checking a BC548B NPN Transistor?

On Tue, 12 Jun 2007 10:36:59 -0500, John Fields
<jfields@xxxxxxxxxxxxxxxxxxxxx> wrote:

On Tue, 12 Jun 2007 10:33:08 -0500, John Fields
<jfields@xxxxxxxxxxxxxxxxxxxxx> wrote:


For example, see page 20 of:

http://www.triplett.com/man/84-704.pdf

---
Oops...
Page 21.


Yes John, but that condition only applies when the polarity reversal
switch is in the AC- position.

Under normal operation, say when measuring DC voltage, you would
connect the RED lead to the more +ve end of a component. That is the
reason why ALL analog (moving coil) meters have a RED lead socket and
a BLACK lead socket - so that when you first connect to a DC voltage
source you would always place the RED lead (RED socket) on the more
positive point in a circuit so the meter pointer doesn't swing
backwards against the end stop and get damaged.

Now if the polarity reversal switch was left in the AC- position from
a previous use, then you may forget to set it to the normal AC+
position before connnecting the RED lead to a +ve source, and the
pointer would bounce hard against the end stop.

My good old AVO model 8 MkIII doesn't have a polarity reversal switch
and neither has any other analog meter I have used, or owned, had one.
The Brits figured that having another switch to check before
connecting the leads was more trouble than it was worth.

When measuring diode junctions with the Triplett you would normally
start off with the polarity switch in the AC+ position and this would
mean that the RED lead was -ve wrt to the BLACK lead and vice versa.
.

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