[Amps] SB-220 and load mismatching...

[Steve Katz]

I don't see how you could hurt the tubes operating into a mismatch.  If you hurt anything, it's more likely to be the load capacitor.

I used to operate the SB-220 into a 4:1 VSWR or so on 80m quite often, since that's the normal band-edge mismatch for a midband tuned 1/2WL dipole on that band!  Never had a problem, never even arched the capacitor but that was a concern.

WB2WIK/6

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
Behalf Of Jeff Carter
Sent: Monday, March 02, 2009 2:27 PM
To: amps at contesting.com
Subject: [Amps] SB-220 and load mismatching...


Hi all,

It has recently come to my attention that folks are running amps into
unmatched loads.  Nobody seems to be worried about VSWR very much.

I've got a SB-220 that I've never run into anything but a 1:1 match.
If I understood correctly back during college, if I'm running 500W out
into even a 2:1 that means I've got something like 50W on the line
coming back at me, yes?  I'm using RG-8, and the line loss is
negligible for the length and frequency involved.

My question is, how forgiving is the SB-220 of VSWR mismatches?  What
is the maximum mismatch that you personally have run or seen run with
this amplifier?  The reason I'm asking is that I've got a 80m dipole
that presents high SWR on other bands (of course) but if the SB-220
will let me get away with it, I'd like to try it.

What I *don't* want to do is screw up these brand new tubes.

Thanks,

Jeff/KD4RBG
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