After reading all the other replies up to this moment, let me ask if you:
1. remove the radio (i.e. run the amp without the radio connected at all)
what do you get (if any reading of forward and/or reflected power), and
2. leave the radio connected to the amp, but run the amp without drive
power at all, then what do you get?
3. Can you vary the drive level (say down to lower levels) and still see
the SWR go up.
From what was written below, its not clear for sure if you are implying
that the amp did have a proper level of RF drive or not. But, I'd still be
interested in knowing if you get forward power and/or reflected power with
the amp turned on but without drive. I've actually had amplifiers where
the application of power and certain tuning conditions cause extra
frequencies to come out in addition to what was supposed to come out. And,
sometimes I got self-oscillation if the amplifier was NOT being driven
with input drive.

------------- No change to below, included for reference and context---

On Thu, 14 Jul 2005, Joeseph wrote:

Date: Thu, 14 Jul 2005 10:31:05 -0400
From: Joeseph
Newsgroups: rec.radio.amateur.homebrew, rec.radio.amateur.equipment
Subject: What would cause the SWR to go up drastically when I turn my amp on?




This is a very screwy problem. First lets get the set-up of my
radio equipment;

The amp puts out about 100 watts on HF.

RADIO-----2 TRANSISTOR AMP-----SWR METER------ ANTENNA

Note the SWR meter comes AFTER the 2 transistor amp.

Ok, when I check the SWR on my antenna it shows 1.1. When I turn the
amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp
only puts out about 100 watts.

Hmmm.....Ok lets see what happens when I use my 1 KW oil filled dummy
load.


RADIO----- 2 TRANSISTOR AMP----SWR METER-------1 KW DUMMY LOAD

Same thing. The SWR is about 1.5 in to the dummy load, but as soon as
I turn the amp on the SWR meter shows 3.x plus.

Ok, Maybe my SWR meter is screwy, so lets use my Dentron MT3000
tuner with a built in 200 watt dry dummy load and built in SWR meter.


RADIO ----2 TRANSISTOR AMP----DENTRON MT3000

Same thing. The SWR is low without the amp on and goes high when the
amp gets turned on.


Ok, Lets see what happens when I use my Drake L-4B amp instead of the
2 transistor amp.


RADIO-----Drake L-4B-----SWR METER-------Dummy load

Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW
dummy load and the external antenna.

The transistor uses MRF455 transistors. Why would the SWR meter go up
significantly when I turn on the 2 transisor amp, but stay low when I
turn on a Drake L-4B.

I've duplicated this scenario with three different SWR meters, and
different patch cables. Lets me say for the record the SWR meter
comes after the amp, so I'm not looking at a high SWR on the input
side of the amp. This is on the output side of the amp.

?????