[Amps] Ten-Tec Titan 425 - input SWR high

[Gerald Williamson via Amps]

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 at 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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