[Amps] Price per Watt Conversation

[Roger (K8RI)]

75.6% efficiency shows the devices are biased deep into class C, not 
pulsed. Linear should be 60 to 65%. With 4 devices running 1500 to 2500 
PEP total out the heat and junction temperatures should not be a 
problem.  Even linear / digital at 1500 shouldn't be a problem as they 
are running less than 400W per device..
These appear to me to be a major step in the right direction. OTOH we 
should not forget that a tiny (short duration) voltage spike can take 
out a SS device, while tubes are relatively forgiving. Very forgiving 
when compared to SS devices

73, Roger (K8RI)

On 4/23/2017 2:21 AM, Roger (K8RI) wrote:
> On the parallel, PP, the convention has been PP, parallel. Each unit 
> runs two devices, PP with the outputs into a combiner..  Those new 65 
> Volt devices,
> http://www.richardsonrfpd.com/Pages/Product-Details.aspx?productId=1241241 
> rated at 1800 watts ea (one page lists Max as 2KW Carrier) at $250 ea. 
> 4 would be $1,000 and only 375W per device. Less than a quarter of 
> their ratings which should require far fewer efforts at the most 
> efficient cooling per device.
> Actually with 4 of these, 3 KW out is still less than 50% leaving them 
> running well away from the  "1% knee"
>
> NOTE the base, rather than being insulated is the source, so the 
> copper spreader would be at 65 VDC
>
> Running at those levels would require less protective circuitry and an 
> ability to handle higher SWR.  Of course, with that much overhead 
> there would be those who would want every watt they could get out of 
> it even though the circuits were optimized for the legal limit, or 
> relatively close to it.
>
> With 4 devices at $1,000, we are very close to the cost of tubes 
> capable of running any mode at the legal limit.  Even at the 1800 W 
> limit we're looking at 7200 Max which 4 devices should do on SSB.  How 
> ever you look at it these new LDMOS are capable of working the legal 
> limit from 160 through 440 although the LP filters could get kinda 
> messy, but ALL bands with one amp! Now there's something to think 
> about.  OTOH the layout for HF and low VHF wold probably be a problem 
> at high VHF and UHF.
>
> 73, Roger (K8RI)
>
> On 4/22/2017 10:08 PM, Jim Thomson wrote:
>> Date: Sat, 22 Apr 2017 16:53:50 +0000 (UTC)
>> From: Catherine James <catherine.james at att.net>
>> To: <amps at contesting.com>, Manfred Mornhinweg <manfred at ludens.cl>
>> Subject: Re: [Amps] Price per Watt Conversation
>>
>> Manfred,
>>
>>     So would it be better to use 4 or or more devices with somewhat 
>> lower ratings for linear operation?
>>
>>     Is there a cheaper option to use simpler heat sinks that don't 
>> have to be carefully machine, but push them less hard by spreading 
>> the power over a larger number of devices?  What's the practical 
>> upper limit of devices that could be used before creating other 
>> design problems?
>>
>> 73,
>> Cathy
>> N5WVR
>>
>>
>> ##  why not use   4  x  BLF188XR    or    4 x MRFX1K80H ? Is it even  
>> possible to use 2 x devices in parallel in each half of a push-pull 
>> amplifier ?    If it is possible, then the heat could be extracted  
>> over 4 x devices.
>> The TX imd, with 4 x devices run at 1.5 kw, on paper, should be good, 
>> since each device is running at 375 w pep output.   Toss in 
>> pre-distortion, and IMD could be reduced further.
>>
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