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[TenTec] Titan 425

To: <tentec@contesting.com>
Subject: [TenTec] Titan 425
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
Reply-to: tentec@contesting.com
Date: Sun, 24 Aug 2003 12:16:31 -0500
List-post: <mailto:tentec@contesting.com>
Hi Kelly,

Just out of curiosity, what's the amp you are interested in?  Henry 3K Premier? 
 (just kidding but it does seem to be an excellent amp.  You gotta love that 
200 lb. p.s. as long as you don't have to move it around, hi).

I'm assuming the 425 is the amp using the 3cx800s with the p.s. and rf in 
separate cabinets.

I have no experience with that one however I have done some work on input 
impedence with the Centurion.  It is important to have the amp on a very short 
strap to a ground bus, and it helps if the ground bus is short, a foot or two.  
 these 8' long copper bars only lengthen the ground run.  the exciter and amp 
should be kind of close together so their separate straps to the bus are not 
very long but the amp's should be shortest--it should be right where the ground 
line comes in from outside and the transmatch should be right there with it if 
you use one.  The feedline from the exciter to the amp does seem to make a 
difference.  In my case I put a MFJ analyzer on the input, keyed the amp so the 
MFJ would see the tuned input to the cathodes, and experimented with different 
lengths.  I found that (except then the tuned circuit was not resonant which is 
the case with the Centurion up near the top of 75 meters) while the feedline R 
was always 50 ohms +- 2 or so, the reactance varied with length.  The problem 
of reducing this to get nothing but R was a moving target--a certain length 
that worked on one band, say 40 meters would, not surprisingly, be a problem on 
20.  And so on.  I ran out of patience in swapping jumpers of different lengths 
in and out and finally concluded that the best thing to do was to shorten the 
length of the feed between the exciter and amp as much as possible.  It was 
originally around 15' before I discovered length matters, and is now down to 
around 3 not including a line isolator.  

I realize this does not matter to you now, but I thought it might help others, 
especially those who are driving amps with non-TenTec rigs that fold back if 
the swr goes up to 1.5.  TT exciters seem to be robust in output even with 
relatively high swr for solid state rigs.  perhaps that's one reason why their 
amps don't have inputs you can tune.   I briefly considered a small matching 
network between my exciter and amp and rejected it because I didn't want one 
more thing to fool with when changing bands (however it's been pointed out to 
me that a LDG autotuner would take care of this for me).

The Centurion drives to full rated output (1.2 kw pep on ssb) easily on some 
bands--on others it needs a bit more wattage than what comes out of a 100w. 
exciter, and on the WARC bands it seems to top out at around 900 watts (which 
is plenty for me).  Getting grounds and the line between the amp and exciter as 
short and sweet as possible can be a cheap passive way of solving some drive 
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