[Johnson] Question on a Valiant.

[Roy Morgan]

At 03:02 PM 7/8/02 -0400, W4UOC@aol.com wrote:
> > shunt resistor is the wrong value (I have 5.1 Ohm's now).
>
>There was a write up in Electric Radio magazine a few years ago tha the shunt
>resistor changes.  ...I shortened the nicrom wire ... to .202 
>Ohm.  Needless to say your 5 Ohms is much to high.


Valiant owners,

Measuring low resistances is problematic.  Most older meters don't do well 
at all below 10 ohms or so...  DMM's are often better but you must account 
for lead resistance.

The so called "Kelvin connection" with two leads for each end of the unkown 
is needed to get accurate measurements: one set of leads carries the 
current set up in the unknown while the second set of leads measures the 
voltage across the unknown.

Though I have not done it with either of the two Valiants here (yet), I 
think a moderately accurate external milliammeter and a source of low 
voltage, adjustable current could be used to check the readings of the 
Valiant meter.  One connection would go to ground, one to the final 
cathodes, perhaps.  A similar setup would check the grid current.  I do not 
know if the Valiant circuitry depends upon the ground tab of that terminal 
strip to carry the current to the chassis.  If it does, it might be part of 
any errors you are having.

If I remember correctly, the plate current to the finals does pass through 
that rear-apron accessory plug, so with care about the high voltage, you 
could insert an external plate current meter there with out removing the 
thing from its cabinet.  Full plate voltage is present, so please be very 
careful.

The second Valiant just joined the household here, so I have been thinking 
about this meter accuracy problem.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
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