Heathkit Apache TX-1
Glen Zook
gzook at YAHOO.COM
Sat Sep 8 15:59:55 EDT 2007
If there is a good chance that the shunt resistors are
bad then new ones can either be made using copper wire
with the length being calculated from the wire
resistance table in the ARRL Handbook or they are
available from Mouser.
The Mouser part number for a 1% 0.1 ohm resistor is
71-RS1A-0.1 and the cost is $1.19 in single quantities
for a 1 watt and part number 71RS2B-0.1 and a cost of
$1.45 in single quantities for a 3 watt.
Mouser doesn't list a 5.55 ohm but putting a 7.5 ohm
and a 22 ohm resistor in parallel will give a
resistance of 5.59 ohms which is plenty close to 5.55.
The part number of the 7.5 ohm is 71-RS1A-7.5 and for
the 22 ohm is 71-RS1A-22 for 1 watt resistors and they
cost $1.19 each in single quantities. Now the 3 watt
1% resistors are actually cheaper! The part number
for the 7.5 ohm resistor is 71-RS2B-7.5 and the part
number for the 22 ohm resistor is 71-RS2B-22. The
cost for these 3 watt 1% resistors is $0.83 each.
The cost of replacing the meter shunts would be around
$3 if new resistors are bought.
Glen, K9STH
--- Peter A Markavage <pmarkavage at JUNO.COM> wrote:
Obviously, if the .1 ohm plate current shunt resistor
and the 5.55 ohm grid current shunt resistor are off
due to age, deterioration, or abuse, your meter
readings won't be highly accurate to make these
changes in procedure.
Glen, K9STH
Website: http://k9sth.com
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