[AMPS] Solid State amps

[km1h@juno.com]

On Sat, 29 Mar 1997 13:35:23 -0500 (EST) "David L. Thompson"
<thompson@mindspring.com> writes:
>Technology is is place to build solid state 1.5KW amps.  It has been 
>since
>the early 80's when QST published an article on an all band 1KW amp 
>(1982).

Technology maybe but completely impratical then Dave.

>Another amp the "SSKW" was published in QST about 1990 or 91.  Part of 
>the preface to this article talked about all the difficulties in
building 
>a solid state KW (poor IMD, poor regulation etc)

The first real attempt in ham literature to use FET's if I recollect.

 and talked about the Mirage attempt (they did sell a few 50W in 800W out
amps).  Part of the problem is artificial...the FCC won't let a
commercial amp have capability from 24 to 30Mhz and they must take more
than 50 watts to drive....

>Mirage finally gave up per the SSKW preface as there were too many 
>hurdles to cross and the amateur market too small.
>
>Another aspect required for the bigger solid state amps is that the
>traditional 13.8V supplies could not product the 100 to 200A for these 
>amps. Research done in the commercial maket showed that 28 or 50V
supplies 
>were more suited.  I have not seen an ad in a while but Lucas
Thansformer 
>was making high quality 28 and 50V models which is what Ameritron/MFJ
used 
>for the 600W model they sell.  Steve Pan has a prototype 1.5KW model at
>Ameritron/MFJ but so far they want to sell the current models 
>including the newer 3XC800 models and the 1.5KW model would probably cut
into
>AL82/1200/1500 sales.

IMO, MFJ is going off the deep end with so many models; it just confuses
the customer and adds to the cost when common components cannot be
utilized. They would be better off with only 3 tube amps in the line-up. 

I fail to understand the reasoning behind archaic linear LV supplies. The
technology  is mature and parts readily available to build 28 or 50V
switching supplies that are only a tiny premium over a well built linear
of equal ratings.  A ham friend of mine locally is a highly respected
power supply designer of primarily Mil-Spec switchers. He threw together
a 100A 13.8VDC unit  for me that is smaller than a 20A Astron.  I have
him almost convinced to do a 50V 100A unit next. 

As 50V or higher FET's come down in price I am sure we will see more
homebrew of 1500 ++ W SS amps.  A key part of  the pricing problem is all
of the components required for the output filters. They add up to big $$
real fast at those power levels. 

The CB crowd use the 2SC2879 in a quad arrangement of 4 PP modules to
generate 1200W as drivers for their big amps....no filters of course!

>So there are two choices...someone else must build an amateur model or 
>we must homebrew one!  Several on this reflector have been building amps

>for over 50 years.  Even with the higher cost of components today I
still 
>see no reason for the pricing for the JRC or ICOM 4KW models.  A SSKW1.5

>model could easily be built for around $1,000 for the amp deck and a
large 
>Lucas supply runs about the same.  I cannot see much more than another
$400 
>or 500  for control circuitry and cabinet.

I think you are way underestimating the RF deck price Dave. I would
figure $2000 minimum for a 1500W amp with a decent amount of breathing
room (say 2KW capable) and 50V FET's. 

>Rumor is that OH2BH was building SS amps for his Dxpeditions.........

There is no weight savings with a linear PS, but Martii needs the
exercise anyway. 

73.....Carl    KM1H


>Dave K4JRB 
>
>
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