[Amps] Metron MA 1000b Misbehaving

[Paul Marbourg]

Thanks for the input on my Metron amp.  Primary suspect is now a ground loop
effect.  There were absolutely no loose or questionable coax connections,
but plenty of potential ground loop paths.  
 
There is a known history of swamping resistor failure in the Metron, however
(reference to K0BG) I don't think that is the issue here.  The old truck was
totalled, so now I get to re-install everything in a new truck!
 
73,
Paul WN7T

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From: Carcia, Francis A HS [mailto:francis.carcia at hs.utc.com] 
Sent: Monday, October 10, 2005 2:23 PM
To: Joe Isabella; Carcia, Francis A HS; Paul Marbourg; amps at contesting.com
Subject: RE: [Amps] Metron MA 1000b Misbehaving


Yea take that extra length and wind an RF choke around a hunk of 3 inch pvc
drain pipe.

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From: Joe Isabella [mailto:n3ji at yahoo.com] 
Sent: Monday, October 10, 2005 5:10 PM
To: Carcia, Francis A HS; Paul Marbourg; amps at contesting.com
Subject: Re: [Amps] Metron MA 1000b Misbehaving


Also, try lengthening the coax between the amp & antenna.  Hi-Sierra
recommends 20-25 feet of coax for their screwdrivers.  I have a HB copy of
the HS, and indeed it makes a big difference in how it tunes.
 
Joe, N3JI


"Carcia, Francis A HS" <francis.carcia at hs.utc.com> wrote:

Noninductive metal film resistors can take a beating. I suspect you
have a ground loop or loose connection. The amplifier input is not tuned so
it should look like a passive load to the exciter. You may have lost a
bypass cap or ground connection inside the amp when mr. elk hit you.
You might try a dummy load to see if the tuning between the exciter and
amplifier changes to get a match. 
gfz 

-----Original Message-----
From: Paul Marbourg [mailto:zborg at comcast.net] 
Sent: Monday, October 10, 2005 3:15 PM
To: amps at contesting.com
Subject: [Amps] Metron MA 1000b Misbehaving

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 sid! e 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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