Topband: More Amplifier info

[MIKE DURKIN]

Im not sure what part this was now ... it seems to be lost to the thread ....
 
Was it the NXP BLF578XR ? if not has the thought of a HF linear droped because of harmonics,,,, ECT,??
 
Mike KC7NOA
 

 > From: w8ji at w8ji.com
> To: w7iuv at yahoo.com; topband at contesting.com
> Date: Sun, 8 Jul 2012 10:18:27 -0400
> Subject: Re: Topband: More Amplifier info
> 
> Hi Larry,
> 
> All of the links and data agree with what I found here in my measurements. I 
> think the real issue is some very creative marketing is being done, and the 
> factory data sheets can be a bit confusing. They certainly do not contain 
> linear data.
> 
> Here are the main points:
> 
> 1.) The "1250 watt device" is actually about a 800 watt PEP maximum device 
> in linear service. At 800 watts, it is right on the edge of what we are 
> accustomed to for Ham product IMD.
> 
> 2.) A major problem is heat. Because all heat is in one small footprint, it 
> needs a very thick machined copper spreader or liquid cooling, even at just 
> 800 watts PEP.
> 
> 3.) Like any other device, they will fail with mismatch at high power. They 
> absolutely will require SWR shutdown and temperature monitoring.
> 
> If we read all of the links carefully enough to cut through the marketing 
> fluff, we will see every reference link listed (where they have actually 
> tested) agrees with all of this.
> 
> I think what has really happened, is many home or first-time builders have 
> taken the data sheet at face value. They have convinced themselves this is a 
> 1250 watt output device that can be run right into almost any load without 
> worry. Of course, neither of those things are remotely true.
> 
> I understand it is tough to let go of the magic of a single 1250-watt device 
> that slapped on a heatsink without protection, and can be run into a 65:1 
> SWR without failing. But this is really a 800 watt PEP linear device that 
> comes with all the long term baggage of any other similar device, as ALL of 
> those links also seem to agree with.
> 
> At 600 watts it will be pretty clean. At 800 watts about at the lower limit 
> of what cheap tube amps can do. All of this requiring getting the heat out, 
> and shutting it off if SWR goes high.
> 
> 73 Tom
> 
> <<<<<Like Tom, I am convinced that it is not possible to run that part at 
> full power in normal amateur service due to the heat issues. Maybe some 
> energetic person will build one up for 1.8 MHz using cryogenic cooling and 
> let us know how that works out...
> 
> 73,
> 
> Larry - W7IUV>>>> 
> 
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