Heathkit Apache TX-1

Peter A Markavage pmarkavage at JUNO.COM
Sun Sep 9 03:26:10 EDT 2007

My point was that one would have to determine if the resistors are still
within their 1% tolerance to be assured that their plate and grid current
meter readings on the Apache are accurate. Buying or building the shunts
was not the issue. For both of my Apache's, I built new shunts, since the
original shunts for the plate and grid meter readings went out of
tolerance back in the 80's.

Pete, wa2cwa

On Sat, 8 Sep 2007 12:59:55 -0700 Glen Zook <gzook at YAHOO.COM> writes:
> 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

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