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LF: Alternatives Re: STW34NB20 - used in a number of MF and LF PA design

To: "[email protected]" <[email protected]>
Subject: LF: Alternatives Re: STW34NB20 - used in a number of MF and LF PA designs
From: Laurence KL7 L <[email protected]>
Date: Mon, 13 Oct 2014 16:15:41 -0800
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Alan/Jack/Stefan/Steve and all - thanks for the feedback, and as described its all a matter of compromise but the new vertical structure  FET Mesh designs seem to be reasonable with similar the lower R on ohm figures of the older devices - rise and fall times/input cap and gate charge all look dooable - just the dollar amount...
Just for info - Ive taken the plunge and ordered
STW70N60M2  600V VDs  0.031 Ohm on and Imax as 68A  - Ill let you know how they work in cct but it looks like completely over the top Gold over engineered FET device but I need the insurance give the changes and sudden animal interventions/weather I get up here in Alaska -
I  temp switched over to a 600V FET, the end of life or about to be
this is a "smaller" I tot device and gets a little warmer than more lower Ron ohms 34NB20 but was running fine in 1Kw W1VD design with no change in tap points out optimizing the Voltage/Current ratios.... I have a pair of them at 300W out and effieciency was about 72% or so. I didnt see any peaky waveform on the drains either..
All being well Ill be on WSPR2 630m tonight - weather up here is far too warm - lake ice has melted  and the ducks and Swans are back enroute South
Laurence KL7L


From: [email protected]
To: [email protected]
Date: Fri, 10 Oct 2014 19:03:39 -0700
Subject: LF: Re: : Re: STW34NB20 - used in a number of MF and LF PA designs

Hi Laurence
There is no easy answer to that problem.  If there were some way you could reduce the time it takes to shut down the final using a faster circuit, it would reduce the chance of smoked FETs obviously.  I guess it's the high winds that really cause the biggest problem there. The close proximity of our trees here limit me from leaving the amp unattended during winds.
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