I didnt say it wasnt. Ive no idea what temperatures are encountered in those
crammed USAF equipment racks. My 432 amp has a 2700W Pd tube in order to get
1000W as an AM linear; all that heat goes somewhere and the manual doesnt
indicate what the external coax should be.
My relay, feed and antenna system cant handle close to what that tube can do
on CW/SSB !
The most Ive pushed it is 1200W and normally run 800W which is 3dB above the
AM-6155.
Carl
----- Original Message -----
From: "Mark Bitterlich" <markbitterlich@embarqmail.com>
To: "Carl" <km1h@jeremy.mv.com>; <amps@contesting.com>; "Louis Parascondola"
<gudguyham@aol.com>
Sent: Monday, October 14, 2013 4:46 PM
Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp
When subjected to external heat, the best coax to use is a teflon
dielectric.
Mark
wa3jpy
----- Original Message -----
From: "Carl" <km1h@jeremy.mv.com>
To: "Mark Bitterlich" <markbitterlich@embarqmail.com>;
<amps@contesting.com>; "Louis Parascondola" <gudguyham@aol.com>
Sent: Monday, October 14, 2013 2:40 PM
Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp
Teflon is very prone to cold flow as are some foam cables.
Neither should be subjected to sharp bends and the manufacturers specs
should be followed.
RG-213/214 type dielectrics are much less prone to cold flow but are very
susceptible to heat flow from the center conductor.
Use of the correct cable and installation procedure for the job usually
works.
Several VHF amps use a coax stub filter to meet FCC requirements. If the
end isnt properly finished corona can develop and eat away the
dielectric, even Teflon.
My 432 amp is ex military and was used as a 1000W output AM linear and
the internal interconnects to the Type N output connector have no sharp
bends, just a few gentle swoops.
Carl
KM1H
----- Original Message -----
From: "Mark Bitterlich" <markbitterlich@embarqmail.com>
To: <amps@contesting.com>; "Louis Parascondola" <gudguyham@aol.com>
Sent: Monday, October 14, 2013 12:44 PM
Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp
Louis,
This phenonamom used to be seen quite regularly in certain military
aircraft where coax types such as RG-214, RG-213, RG-217 were used. Any
kind of medium to sharp bend at all, co-located with a heat source
caused it as you mentioned. Typically around turbine compartments or
bleed air lines.
All of these coax runs were eventually replaced with Teflon dielectric
types, such as RG-142 & RG-393. That lesson learned, all of my amps
have been re-plumbed with the same teflon type coax. :-)
Mark Bitterich
wa3jpy
----- Original Message -----
From: "Louis Parascondola" <gudguyham@aol.com>
To: <amps@contesting.com>
Sent: Monday, October 14, 2013 12:17 PM
Subject: [Amps] repair of older Command Tech VHF-2000 amp
I performed what seemed to be a rather odd repair on an older Command
Tech VHF-2000. I thought I would share this since it could possibly
affect the HF models. This particular amp like most has a piece of coax
that comes off the output of the tank circuit and goes over to the
antenna relay. In this case a harmonic filter. The coax was affixed to
the side of the wall and dove down to the bottom and over to the relay.
Filter in this case. There was what seemed to be a soft arc to the coax
as it bent over the edge and down. The amp exhibited no output
whatsoever and acted like there was not antenna connected. I tracked
down the problem to that coax being internally shorted. An autopsy of
the piece of coax was amazing. Apparently the owner of this amp operated
digital modes like JT65 so I would think there were many periods of
heavy duty cycles. Apparently over time the dielectric center conductor
heated up and little by little the wire migrated to the outer edge and e
ventually broke through at the "arc" strain point and shorted to the
braid. Several inches of the center wire was way far away from the
center of the dielectric. Go figure.
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