Envelope-to: dave@picks.force9.co.uk
Delivery-date: Mon, 04 Jul 2005 21:55:48 +0100
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From: "Scott Tilley" <sthed475@telus.net>
To: rsgb_lf_group@blacksheep.org
References: <NKEMLGOEKANPNJOBFBAFGEJBCFAA.g4wgt@tiscali.co.uk>
Date: Mon, 4 Jul 2005 13:57:26 -0700
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Subject: LF: Re: RE: G0MRF 300w Tx PA mods
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Gary

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...

Scott
----- Original Message -----
From: "Gary - G4WGT" <g4wgt@tiscali.co.uk>
To: "Steve McDonald" <jsm@gulfislands.com>
Cc: "LF (Rsgb LF Group)" <rsgb_lf_group@blacksheep.org>
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
about
> 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
> (G0MRF).
>
> Any thoughts or ideas ??
>
> Regards,
>
> Gary - G4WGT - IO83qp
>
> Web : http://myweb.tiscali.co.uk/wgtaylor
>
>
>
>
> -----Original Message-----
> From: Steve McDonald [mailto:jsm@gulfislands.com]
> Sent: 28 January 2005 22:50
> To: g4wgt@tiscali.co.uk
> 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
getting
> very scary as the cores will saturate all of a sudden...be 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
>
> Web: "THE VE7SL RADIO NOTEBOOK" at   http://www.imagenisp.ca/jsm
> [L.F. Loops] [Tuna Tin DX] [H.F. Maritime DX] [Crystal Radio DXing]
> [2200m Band] * NEW [CQ Crossband - 2200m To HF] [NDB DX] [Boatanchors]
>
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