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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