From: "Jeff AC0C" <keepwalking188@ac0c.com>
To: "Ken K6MR" <k6mr@outlook.com>, <amps@contesting.com>
Subject: Re: [Amps] RF2K+ LDMOS linear
<For me, especially with RTTY contesting, the capability of running this amp
<on a So2r basis should not be assumed to be workable until it's actually
proved. This gets back to my main point. The gee-whiz it will be perfect
buzz on a lot of tech really needs to come with a list of disclaimers to
cover the exceptions and restrictions. But they never do; meaning the only
way to really get a handle on them is for someone to get one and give it a
hard workout. That would at least be one solid data point.
And you can't really make a compare to the Elecraft stuff - the same issue
confronts the KPA1500 (it's an unknown new entity - until it's proven in
combat). However they have a proven track record of making a decent product
and improving it when there are issues. These other various guys who want
to get into the amp biz are unknown entities by comparison and while they
may build perfect products and have perfect support, to my thinking until
that's actually proven it needs to seen with a skeptical eye until proven
otherwise.
73/jeff/ac0c
### The flex power genius video depicts ONE FLEX xcvr and ONE FLEX
power genius amp, running 1.5 kw on CW...and toggling rapidly back and forth
between
40 + 20m. So no, you dont require two amps. If a 120mm fan is good, a 150mm
is even
better, esp when 2 are used in push-pull. Typ 150mm fan is 234 or 243
cfm..like the papst,
with ball bearings. Stick it in another room, or in a sound proof box, end of
noise issue...and end
of cooling issues. At work, we would put noisy printers inside these sound
proof boxes, with flip up
plexiglass covers. They were lined on 5 x sides with honey comb foam. Dead
quiet with that lid down.
## the only fly in the ointment, when toggling between any two bands is if the
auto tuner is used on both the 2
bands in question. But with the use of relays, and no motor driven caps,
their simple relay switched L network
would still switch bands fast like. IF the tuner was only required on just one
band, then the tuner would be bypassed when
toggling to the 2nd band.
## the acid test is simple, stuff 1.5 kw CCS CXR through the auto tuner into
an outboard manually operated tuner....which is
mal-adjusted so the swr = 3:1....then into the big dummy load. Then let is
sit for at least 1 hr...and see what happens. Do
this on 160, 20, 10m . If it doesnt blow its brains out, you have a winner on
your hands. Ok, then let some rtty contester beat on it
for 48 hrs. For rtty contest, leave the fans on full bore CCS for the entire 48
hrs, ditto with any contest. Dont let stuff heat up 1st..then
try and play..catch up.
## 13 db down for the 3rd harmonic means 75 watts reflected back to the
combiner. How many db down is the 5th and 7th and 9th harmonics ?
That 75 watts is not absorbed by any LP filter, nor is it routed to ground.
The combiner is not a tuned circuit like a PI net, so the 75 watts has nothing
to bounce off of. So where does it go ? Probably back into the PA. This
would be a good application for a Diplexer setup... which is just a LP and HP
filter
with their inputs in parallel. Output of LP filter goes to TR relay to ant.
Output of HP filter goes into a 50 ohm dummy load. Flex used 7 x diplexers
on its latest..power genius..with an on board 50 ohm dummy load. The 7 x HP
filters only have to handle low power, like the 75 watts from the 3rd
harmonic, plus what ever level harmonics on the 5-7-9. Simplest method
would be to either use an onboard 50 ohm dummy load, or route some 58 or 213
through a SO-239 then into an external dummy load. There goes another huge
load off of the heatsink. 2nd harmonics is typ –40..as more on the 4-6-8th
harmonics, typ of any push- pull arrangement.
## The serrated heatsink concept is a good one, easy method to increase
surface area. Eimac used serrated fins on some of its tubes... depicted
in some of their qst ads a long time ago. Notice that Eimac uses very very
thin fins and lots of em, on their 3CX-3000A7 and also 3CX-6000A7.
On both those tubes, what you think are thick fins at the top and bottom are
actually struts.....used to support the large diam cylindrical piece
that surrounds the internal thin fins. With either tube sitting vertical on
a white sheet of paper, with loads of light on the paper, and viewed from
above,
you can clearly see the myriad of paper thin, silver plated copper fins, going
out like spokes of a wheel. At their outer edges, they are fold back a bit,
like a hairpin.
## yaeus got it right with their 100% copper heatsink they used on their 400
watt version of the FT-9000MP. Aluminum only conducts heat 57% as good
as copper. Copper will extract heat a lot faster than aluminum. I have tested
this. But you then still have to transfer that heat ...to the air.
A copper spreader plus serrated aluminum heatsink + high cfm fans, esp in a
push pull arrangement should suffice for all demanding needs.
## pre-distortion output on the german or any other amp, ss or tube, should be
standard. A pair of gigavac GH-1 relays, sped up for qsk, one on the input,
and one on the output would ensure 100% reliability for qsk cw...or vox cw +
ssb. With a vac relay on both the input + output side, then the amp will
handle 2 kw on bypass mode. That comes in handy when calibrating the internal
wattmeter, using a 2nd amp..with 1st amp on bypass mode. Also
comes in handy when wiring 2 amps nose to tail in series, like for a redundant
setup. A simple spdt relay, or switch ensures only 1 amp can be keyed
at any one time. Any gigavac vac relay can be bought with either a 12 vdc or
26.5 vdc coil. They are field replaceable too...so you can easily swap to a
different voltage coil if you like. If you are voltage limited, the 12 vdc
relays can easily be sped up with just 18+ vdc. A dc to dc converter could
also be
used to obtain the required higher vdc, if the amp only has a 12 vdc lower aux
source. Or the 50 vdc could be used, with correct drop resistor. To speed it
up even more, the correct value cap can be wired in parallel with the drop
resistor. Now you are down to 1.6 msecs..which is ample for qsk.
## If the LDMOS devices become unobtainium down the road, I would buy
spares, NOW,at the same time the amp is purchased.... and store them away.
If the LDMOS devices blew up, buy some new ones, if still available, and not
touch your stashed away spares. Then at least if and when they become
unobtainium, you have a working set in the amp..and spares, which means the amp
is still usable for a long time...and also has a high resale value.
Or just replace the entire pallet with the latest and greatest devices.
Jim VE7RF
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