Hi there.
Shortly before ramming my SUV into two large elk while mobiling during the
WA state salmon run last month, I observed something a bit odd with my
trusty old Metron amplifier. While fine tuning my Hi-Q 160-5 antenna (while
stopped along side the road) on 160 meters, I was monitoring the SWR between
the TS-50 exciter and the amp's input, as well as between the amplifier's
output and the remote-controlled shunt inductor feeding the antenna's base.
I used a MFJ cross needle peak reading VSWR right after the exciter (with 4'
run of RG58U then on to the amp) and a RadioCraft 3000 remote sensor right
on the amp's output (with about a 10' run of RG8U to the shunt to ground
roller inductor at the antenna's base). When I made a flat match between
the amp and antenna, there was a somewhat elevated VSWR (1.5:1 ?) between
the exciter and amplifier. When I made a flat match between the exciter and
amp, there was a significant VSWR between the amp and shunt inductor at the
antenna's base. Given the wavelength on 160 meters, I would not expect any
significant variation in VSWR at the two different path insertion
measurement points. Therefore, I am beginning to suspect that the input
swamping resistors in the Metron may have aged to the point that their
non-reactive resistance has shifted away from the 50 ohm network value.
As I recall, the design uses four paralleled 200 ohm 2 watt metal film
resistors for swamping and another set of the same for an input attenuation
pad prior to the four port input splitter. Does anyone out there have some
experience with repairing the Metron? I have yet to do a visual on the amp.
May I presume to hold the four paralleled 200 ohm swampers as the primary
suspects? These guys are reactively compensated with L1 & C3. Any history
of C3 failure? I would expect to see heat damage on the swampers if they
have been overdriven by accident/failure.
Thanks & 73,
Paul WN7T
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