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@att.net>
To: <amps@contesting.com>, Manfred Mornhinweg <manfred@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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