[TenTec] Titan 425 Initial Tune-Up settings - high VSWR

[CSM(r) Gary Huber]

After careful review you are correct ("a rose by any other name is still a 
rose"..W.S.).


73 es DX,

Gary - AB9M

-----Original Message----- 
From: Dr. Gerald N. Johnson
Sent: Thursday, November 25, 2010 1:06 PM
To: tentec at contesting.com
Subject: Re: [TenTec] Titan 425 Initial Tune-Up settings - high VSWR

The manual I have shows individual input circuits called low pass
filters on the input low pass filter board. 81223. There is no more
output filter after the PI-L. There is one per band from 160 through
10m, two positions for 160 use the same 160m filter like the two 80 and
75 meter positions use the same filter.


Input tuned circuits typically have very low Q like Q of 1 because in a
grounded grid having comparable Q in and out makes it very difficult to
tune because of interaction between the circuits.

The list won't accept an attachment.

73, Jerry, K0CQ

On 11/25/2010 11:46 AM, CSM(r) Gary Huber wrote:
> 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 at 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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