[Test-Equipment] TV-7 Calibration

[WA5CAB at cs.com]

DW,

As a philosophical statement, DVM's waste time when working on boatanchor 
gear.  The natural tendency is to sit there and fool with the adjustment until 
the meter or counter reads exactly what the book says.

However, whether the meter impedance will make any difference to any given 
measurement depends upon the source impedance.  It could make no difference, a 
little difference or a bunch.  For example, the BC-611 maintenance manuals give 
two charts for most test voltage settings, one using a battery operated VTVM 
and one using another meter.  Some of the numbers are the same and some are 
quite different.  

But if you want to make sure to set the thing the way it would have 
originally been set, the TS-382(*)/U is 1000 ohms per volt on all AC ranges and 
selectable either 20,000 or 1000 on all DC ranges.  That being the case, if the 
instructions don't tell you which to use, it's probably safe to assume 20.000.  If 
you shunt the meter probes with (20,000 x full-scale range) ohms, the TV-7 
won't know you aren't using a TS-382.  :-)

In a message dated 10/11/2007 11:01:37 AM Central Daylight Time, 
tubestuff at comcast.net writes: 
> Hello,
> 
> I'm getting ready to go through a TV-7/U, step by step using the Depot 
> manual (TM-11-6625-274-35). The first step, the bias voltage test calls out a test 
> setup then asks for a reading of 3.0 +_.1 Volts. I'm reading 5.26 Volts.
> 
> My question is this. The procedure calls for using a TS-352 Multimeter. The 
> only meters I have are high input impedance DVM and a VTVM. I know that a 
> TS-352 will load the circuit and cause a lower reading. Is there anyway to make 
> the necessary adjustments using a DVM or a VTVM? Is this a situation where I 
> will need to get a good quality VOM (Simpson 260 etc) to do the adjustments? 
> What is the ohms per volt on a TS-352?
> 
> Thank you in advance for any suggestions.
> 

Robert Downs - Houston
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