Date: Tue, 6 Dec 2016 18:30:27 -0500
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: [Amps] SS amps and auto-tune. Is it even necessary?
With first generation SS amps, auto tune was almost a necessity, BUT
with the new amps?
With the current flock of transistors that can handle the wrong antenna
or even an open circuit, auto tune is just a convenient, but expensive
accessory. A manual tuner will work just fine.
Of course we are still in the "if you want one, you'll have to build it
yourself" stage. OTOH amplifier, combiner, and LP filter kits are
available and the cost is reasonable. IM is also on par with the best
tube amps.
50% Vs 60%. Who cares? They are easily water cooled without the
headaches of water cooling a tube amp..
73
Roger (K8RI)
## You may well be correct, but to put out 1.5 kw into a 2:1 swr.....or
higher, the amp
will have to be configured to put out 2.5 kw + into a dummy load.
## I have yet to see any of these SS amps with good imd, who makes one ? Im
not seeing
good imd with any of the published ldmos devices.
## K9YC pointed out that these SS amps have min imd, when into a 50 ohm 1:1
swr. IMD
degrades when into any amount of swr.
## Having to use a manual tuner with a SS amp is a pita, defeats the entire
purpose of the SS amp.
## The combiners and LP filters are not cheap...esp when they have to handle
1.5 kw CCS into a
2:1 or higher swr.... hence another reason for the auto tuner. The LDMOS
device may well handle a
sky high swr for an extreme short period of time... but the LP filters wont,
nor will the combiners..or pin
diodes if used for TR qsk.
## water cooled tube amps are a non issue. The anode fin assy is removed and
replaced with a few turns
of cu tubing. Some versions have a sealed assy built around the anode, with 2
x water leads + standard fittings.
they are typ morphed into teflon tubing, or similar, then into the heat
exchanger /radiator, with a fan on it....to
dump the extracted heat. At 3.41 btus per watt..and say 1.5 kw anode
dissipation = 5115 btus
## A real small radiator will handle 5k btu’s easily. My 2nd auto tranny rad
in my mustang is small,
only .75 inch thick, and only 11 inch wide x 7.5 inch tall. Rated for 13,000
BTU... = 3.8 kw CCS.
The 5.75 inch tall version is rated for 9,800 BTU = 2.87 kw CCS.
## water cooling with the smaller tubes is a pita. Typ used for industrial
heating applications, where the
load can be all over the map, and the higher anode dissipation comes in handy.
## water cooled SS amps may well be the ticket, provided no leaks, isnt
subjected to freezing, doesnt corrode
the AL / cu radiator used, hits the dew point / condensation issues etc, etc.
100% distilled water with no corrosion inhibitor in it could easily destroy
the radiator assy. But we are not talking about
HV here, only low voltages like 50 vdc...so corrosion inhibitor or water wetter
etc, could probably be used ok.
## Doesnt matter which way you slice it, the SS amp will cost a bunch. The
$10K dishtronix ss amp doesnt have an
auto tuner, has lousy -30 db pep IMD3.... but its price and complexity
reflects the efforts involved.
## The low cost of the LDMOS is the least of the issues involved. Its
everything else that’s involved with the SS amp.
Jim VE7RF
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