There are no individual tuned input matching circuits on a Titan 425.
Basically the exciter drives the cathodes of of the two 3CX800A7s. The
recommended feedline between the exciter and the amplifier is a short length
of RG-58. I have a Dow Key relay in line (to use either a CORSAIR II or
OMNI-VII as the exciter) and a Dentron W-2 (dual meter) in line to monitor
driving power and VSWR, so I use short lengths of RG-8X.
I previously replied but that email is being held until moderator review as
I attached the circuit diagram of the RF deck.
73 es DX,
Gary - AB9M
-----Original Message-----
From: Rob Atkinson
Sent: Thursday, November 25, 2010 10:15 AM
To: tentec@contesting.com
Subject: Re: [TenTec] Titan 425 Initial Tune-Up settings - high VSWR
Hi Gary,
You never said what your load Z was but it together with your feedline
length could require more inductance in the amp's pi network.
Once you adjust the "tune" and "load" caps for maximum output you
should increase loading a bit. This can be confusing. Ten Tec labels
their capacitors 0 to 10 with 10 being maximum capacitance (plates
meshed). You therefore decrease capacitance just a bit to increase
the loading. Watch the grid current when you do this.
I'm interested in how Ten Tec does input Z matching on the old Titan.
It is possible that the bandswitch in addition to switching taps on
the output pi network coil, also switches different tuned matching
circuits on the amp's input. so when you switched to 80 m. you
inserted a different input matching circuit.
73
Rob
K5UJ
<<<During the past weekend I participated in the phone Sweepstakes and
observed
high VSWR on my OMNI-VII while driving my Titan 425 using the published
settings for 75 meters when operating between 3.8 and 3.9 MHz.
The manual suggests; BAND 75, TUNE 5.5, LOAD 7.5, FREQ 3.9 MHz. but with
BAND
75 selected the load control was near 10 and the driver VSWR was nearly 10
to 1!
By switching the Titan bandswitch to 80, the LOAD setting became 3, TUNE
stayed
at 5.5, FREQ stayed at 3.8 – 3.9 and the VSWR dropped to 1.1 to 1.
Over the twenty plus years I’ve had this Titan 425-E as the original owner,
I
had seldom used it on 80 and even less on 75 so I had not observed the high
VSWR. A new OMNI-VII with its “High Current” notification and shut-off
protection got my attention to the fact and drove me to the solution.>>>
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