Thank you Gerald.
Yes sir, I totally agree with you about the Z/vswr variance because of the
applied drive level.
The analyzer test was done to get a ball-park figure, par se.
Prior tests (inadvertently omitted in my OP) with the actual exciter
connected and driven at 50W, then 80W, also resulted in very high (>2) swr
at the input.
You are probably correct about the amp being 'NAD', however, as I'm a
newbie to the Titan 425, I wanted to hear from other experienced users of
this model - before telling my friend to use his amp "as-is" with an ATU in
between.
73,
Prem
www.qsl.net/va3uma
On Sun, Oct 19, 2014 at 10:15 AM, <TexasRF@aol.com> wrote:
> Prem, a cathode driven amplifier input impedance (and resulting vswr) is
> determined by cathode current primarily You can't get enough cathode
> current flow with a low power rf source such as the MFJ analyzer to create
> the impedance (and resulting vswr) you expect.
>
> To make a valid test, you need to connect a vswr meter between the
> transmitter and the input of the amplifier. Then perform the input vswr
> checks using the normal driving power that is used on the air. You can
> easily see the effects of input vswr as the driving power is reduced.
>
> With the data you provided, it is very likely that there is actually no
> problem.
>
> 73,
> Gerald K5GW
>
>
> In a message dated 10/19/2014 8:03:04 A.M. Central Daylight Time,
> va3uma@gmail.com writes:
>
> Friends, for a long time now, the input SWR on my friend's Ten-Tec Titan
> 425 is very high (average > 2 on all bands) - when measured with a MFJ
> analyzer at the input - with a 50R dummy-load at the AMP output.
>
> So long, he's used an ATU between the exciter and the 425, but I'd like to
> find out if there's way to fix this SWR problem (no slug-tuning. fixed L
> and C in the i/p LPF).
>
> I've already checked/assessed the following:
> 1- Amp gives full o/p of 1500W pep on a DL with an ATU between the exciter
> and the amp (so, tubes should be OK ?)
> 2 - The vacuum relay contacts test 100% OK with a multi-meter continuity
> test.
> 3 - No visual or smell indication of any burns/arcing/toast - in the I/P
> LPF or in any other circuit elements.
> 4 - Band switch contacts look good. Cleaned with De-Oxit - just to be on
> the safer side.
> 5 - Ig and Ip are as per specs
>
> Any help/lead is appreciated.
>
> 73,
> Prem
> VA3UMA
> www.qsl.net/va3uma
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>
>
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