Hi Don, et al,
The simplest way is to determine the actual resistance of each cathode
resistor of the finals, then measure the actual voltage across each
resistor while idling, or under some load, use ohms law to calculate the
actual current thru each resistor, add those 2 numbers and you have the
cathode current (including plate, and any screen current, which is
pretty small) and compare that to what the meter reads. Then if you
want, change that "test selected" resistor as needed.
73,
Al, W8UT
www.boatanchors.org
www.hammarlund.info
"There is nothing -- absolutely nothing -- half so much
worth doing as simply messing about in boats"
Ratty, to Mole
On 10/7/2010 8:00 PM, Don Cunningham wrote:
The question I have is what is a simple way to check to see that our
meters are not "way out in left field" setting this bias after all these
years?? I remember seeing this years ago, but is there a safe place we
can open and put our DVM's in line and read that .7 mills and adjust as
needed?? I am sure those resistors have moved just like others in our
rigs, and I know it pays to "get it right" if we want these tubes to
last. I think the resistors that are "selected to match" are noted on
the schematic, but not sure about that.
73,
Don, WB5HAK
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