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LF: Re: RE: G0MRF 300w Tx PA mods

To: [email protected]
Subject: LF: Re: RE: G0MRF 300w Tx PA mods
From: "Scott Tilley" <[email protected]>
Date: Mon, 4 Jul 2005 13:57:26 -0700
Delivery-date: Mon, 04 Jul 2005 21:55:48 +0100
Envelope-to: [email protected]
References: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]

Usually core saturation will cause the over current protection to trip and
save the finals...  I figure you have an SWR problem...  I haven't had time
to read the thread forming but that seems like to cause of concern...  I
have run my variant of the G0MRF amp at over 600W in the 41V region for
months at a time with no problems until the SWR went crazy... ZAPP! and off
to the bench you'll go...  If you can use an SWR protection circuit or a
loading arrangement that causes the system to fail gracfully, I found link
coupling does jut that here so when it rains or snows the power drops off
and SWR failures don't happen...

----- Original Message -----
From: "Gary - G4WGT" <[email protected]>
To: "Steve McDonald" <[email protected]>
Cc: "LF (Rsgb LF Group)" <[email protected]>
Sent: Monday, July 04, 2005 7:28 AM
Subject: LF: RE: G0MRF 300w Tx PA mods

Hi Steve & LF,

On 28th January 2005 you included the following statement in your e-mail.

""I think Scott has found that anything over 43V at 15A is getting
very scary as the cores will saturate all of a sudden...""

It seems that t has just happened to my PA, although my readings were
showing 36 volts at 14 Amps (504 watts), I was testing again & tweaked the
volts up a bit from 34 volts at 12 Amps (408 watts), it only stayed on
30 seconds & failed.

During testing after the mods were carried out I bench tested into 50 ohm
dummy load & achieved 645 watts so I felt that I could procede a little
higher into the antenna, the antenna readings looked fine using Jim's
(M0BMU) LF Tuning Meter. So I wonder, was it core saturation??

The core I am using is the original which came with the kit from David

Any thoughts or ideas ??


Gary - G4WGT - IO83qp

Web :

-----Original Message-----
From: Steve McDonald [mailto:[email protected]]
Sent: 28 January 2005 22:50
To: [email protected]
Subject: Re: G0MRF 300w Tx PA mods

Gary - it sounds like you are getting similar results as we are with our
'west coast half-killowatt' amps. I am wondering what toroid you are using
in the output xfrmr? Both Scott (VE7TIL) and I are using salvaged TV cores
which seem to be OK up to a limit...they all appear to be slightly
different. I think Scott has found that anything over 43V at 15A is
very scary as the cores will saturate all of a careful with
yours and get as much cooling on it as you can. I am thinking of rewinding
another output xfrmr with the same turns ratio but with two cores stacked
together. Good luck with yours.

Steve / VE7SL

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