I am in the middle of repairing an old Waters 334 dummy load wattmeter
for a local ham. He had picked this up at a hamfest and the meter
didnt work. I have removed the oil tank and cut an opening in the back
to access the internal components. The oil has been drained into jars
and I will put the oil back after I make the repairs.
Ok, here is the question.
The failure is the diode. it looks to have the original diode. Black
glass marked SG5409. I do not see a modern cross or the exact type
still available. Is there a better or more durable RF diode that will
work in this circuit? Temporarily, I soldered in a 1N4148 and this
seems to work well at the 100 watt level. My concern is at a KW will
this hold up? What about the possibility of stringing several 1N4148's
in series to increase the voltage capability? I know that most of the
power is going into the 50 ohm resistor and the diode is just seeing a
small sample. The diode is in series with four 2.7 ohm resistors and
then has a 15K fixed and a 10K pot before it gets to the meter. This
is on the 1KW position. Any suggestions will be appreciated.
73, Randy, w5kcm