[Amps] Combining Two Amps & Adding a Filter?

[doc <kd4e@verizon.net>]

Thanks for this list!  I have often read excerpts from the archives
over the years.

I am in the process of combining a pair of eight 2SC2879 KW amps
for 160-10M and need some help as I make this work.

In addition to a splitter and a big combiner I need to build a
switched HF filter.

I started by purchasing the RF Electronics filter kit: 
http://users.aol.com/rfelectron/filter.htm  but it is hopelessly
underrated.

I then started looking at filter designs and came upon the
CWAZ and it seems to make good sense.

I read an old (2000) post to the AMPS list re. the CWAZ filter
and big HF amps (see below) but there were no further posts
in the thread.

> See the excellent CWAZ filters by W3NQN in the new edition of the
> Handbook, it offers 60 db attenuation of the second harmonic.  It
> offers much greater performance than the 7 element chebyshev design.
> It would certainly make building amplifiers easier not having to
> worry about the L in the tank circuit.  Craig VK3HE

Has anyone implemented the CWAZ in a high power HF amp design?

The CWAZ uses one additional capacitor, adding to the cost, but
offers superior filtering.

I also noted that in the 1999 ARRL Handbook a 50W HF amp used
a different filter design with only two inductors and five
capacitors.  I wonder if that only provided effective filtering
at lower power levels for some reason?

RF Parts  www.rfparts.com/combiner.html  appears to have the
splitter and combiner I need.

I plan to order the COM-2 Input/Output     .5 x .5 300W $3.75
to split the 100+ watts of input drive between the two amps and
am thinking of using the COM-6 Output .5 x 1.2 2800W     $6.65

Is there any advantage to choosing one of the larger combiners?
COM-10     Output*     .5 X 2.4     5000     19.95     18.85
COM-20     Output*     1.0 x 2.4     10,000     36.95
*includes 100W termination resistor.

I am wondering about efficiency, heat, bandwidth, etc.

Also, what is the purpose of the terminating resistor for these
two devices but not included with the smaller ones?

Any additional considerations in the implementation of the
splitter and combiner, please?

I noted on my amp schematic that they have added a pair of 225pF
caps stacked on a third to ground at the output of the final
combiner -- what would be the purpose of that, please?

I also observe that at the input they have a 220pF cap in series,
a 120pF cap to ground, and a 100 Ohm resistor across the out
side of the splitter.  Does any of that impact bandwidth and
should I duplicate it on the splitter into the dual amps?

Sorry for all of the questions and the lengthy detail but
tried to anticipate requests for data to save time.

--
Thanks! & 73, doc kd4e
A blessed and joy-filled Christ-mas to all!

West Central Florida  100% Linux.  Suse 9.2
Hallicrafters, Heathkit, Homebrew, TenTec, Yaesu
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