Amps
[Top] [All Lists]

[Amps] Titan 425 Reflected Power

To: "amps@contesting.com" <amps@contesting.com>
Subject: [Amps] Titan 425 Reflected Power
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sun, 24 Sep 2006 14:02:30 -0700
List-post: <mailto:amps@contesting.com>
I'm encountering a strange problem with my Titan. If I follow 
standard practice and achieve a 1:1 match with the exciter, then 
take the amp out of standby, the amp typically shows mismatch on 
the order of 1.5 or 2:1. 

If I then re-tune the antenna for minimum reflected power on the 
Titan, the VSWR at the tuner, and also at a Bird inserted right 
after the Titan, shows a mismatch of 1.5 - 2:1. The mismatch seems 
to be greater at higher frequencies. 

The bridge in the tuner and the Bird are consistent -- that is, 
when the bridge in the tuner shows a match, so does the Bird, 12 
inches of RG-8 from the Titan's output connector. 

I have three different tuners -- a Ten Tec 229B, a Ten Tec 238A, 
and Drake MN2000. It happens with all of them. I've traded cables, 
made them as short as possible, changed the switch that switches 
between the tuners (from a B&W to an Alpha Delta). The exciter is 
going through the Titan to get to the antenna for tuneup. I've 
traded Birds. I've eliminated the Bird. All of the cables are RG-8, 
all are short. 

So you say, go with the bridges. BUT:  Grid current in the Titan 
tends to be much lower when the Titan bridge indicates zero 
reflected power, and rises rapidly when I don't. And grid current 
is the big NO-NO in 3CX800A7's, the output tubes in the Titan. I am 
careful to keep grid current down to an indicated 30 mA for the 
pair (120 mA is absolute max). I can't get close rated power 
without excessive grid current unless I tune the antenna for zero 
reflected indicated on the Titan. 

The SWR indicator in the exciter (TS850) also agrees with the Bird 
and the bridge in the tuner -- IF I bypass the amp's RF circuitry 
and connect the radio direct to the tuner (or through the 
switches). This points to the RF path within the Titan between the 
SO-239 output connector and the final output stage. Has anyone 
encountered this before? Any fixes?  

73,

Jim Brown K9YC


_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>