[Elecraft] LDMOS for QRO

[Edward R Cole]

OK. My reason for mentioning these amps was to answer some of the 
negative points being made in regard to a fictitious KPA1500.  These 
days one does not have to combine a lot of lower power FETs to reach 
QRO.  I gave you a link to the device which is made by 
Freescale.  There are comparable devices made by NXP.

I replied to the argument that one can not run them linear at 
1200w.  To quote myself: "So combining two running 750w each gets you 
1500w in linear operation with 2400w dissipation."  Most RF 
transistors will not be linear if driven into saturation so one backs 
off on the drive and resultant output to improve linearity.

Heat dissipation is taken care of by using copper heat spreaders 
under the transistors coming from all these suppliers unless you buy 
the LDMOS directly (W6PQL uses a 3x5x1/2 inch copper spreader).  I 
would suggest either the amp kits or buying assembled amp pallets to 
build with.

Price: two LDMOS would run roughly $500.  I new 8877 from RFParts is 
$1450 (Eimac) or $665 (Taylor).  Of course you can purchase a used 
8877 in the $350-450 range.  The HVPS will run about $500 and you 
probably would have another $400 in materials to complete a basic HF 
amp with manual tuning (total= $2350 (Eimac) to $1250 (used 8877)).

W6PQL is offering an assembled single LDMOS amp for $825 so two would 
run $1650 and probably another $400 to make a complete 1500w SSB HF 
amp. Surplus HP Blade 50v -50A PS run $30-50 on e-bay.  To run two 
LDMOS you just have two 50vv PS supplying each separately.  Total= $2150.

If you build your own you can save a little off this total - W6PQL 
kit is $563 which includes the NXP BLF-188XR. 
http://www.w6pql.com/parts_i_can_provide.htm  est. total 
2x$563+$400+$100 = $1625

No point belaboring this as there are going to be some amps showing 
up this coming year using these LDMOS devices.

-----------------
From: Kevin Stover <kevin.stover at mediacombb.net>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] LDMOS for QRO
Message-ID: <548DAFBD.7000800 at mediacombb.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

W6PQL has designed and built a 1KW SSPA for 1.8-54MHz using an LDMOS
device. Freescale I think.
he has also designed a pretty stout Low Pass filter designed for 1.5KW
1.8-54 MHz.
He can get 1.2KW out of it at saturation with 2-3 W drive.
A pair of these devices @ 750W could do 1500W all day any mode. but then
the power supply becomes the limiting factor.. 50V at 70amps?

http://www.w6pql.com/1_kw_sspa_for_1_8-54_mhz.htm


73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
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