[Amps] SS amps and auto-tune. Is it even necessary?

[Roger (K8RI)]

To me, an amp is an amp, is an amp be it tube or SS and its sole purpose 
is to give me a louder, clean signal.

When I initially tune up a tube amp it's into a dummy load.  On 160, 74 
and 40, excursions usually call for the antenna tuner which is done by 
switching the aim into the antenna tuner. 160 may require a good change 
in tuning, while 40 may just be a tweak.

Amp is tuned, antenna will show 1:1.0 R=50, switch rig to the antenna.
The SS amp is already tuned, so it just needs an antenna with a 1:1 SWR, 
or thereabouts.  So even with a manual tuner you have remove the tune 
and load cycle on the amp.

Auto tune gives the same convenience whether tube or SS.
It lends itself to making the SS amp close to instant band switching.
With predistortion they produce signals comparable to good tube amps.
We can get legal limit, auto tune tube amps "for a price".

The only drawback I can see is as I said in the earlier post. The "good 
ones" (state of the art, if you will) are still in the realm of the "do 
it yourself", but amp kits, LP filter boards up to 3 KW, and combiner 
kits are available.

Extra headroom is not much different than with tube amps and in general 
you need it for similar reasons.  With antenna tuners, whether manual or 
auto there is no excuse for the amp to see a high SWR, except for 
accidents.  An AIM will let you tune far more accurately than is necessary.

73

Roger (K8RI)

On 12/7/2016 7:24 AM, Jim Thomson wrote:
> Date: Tue, 6 Dec 2016 18:30:27 -0500
> From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
> To: "amps at contesting.com" <amps at 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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