We have joked on the Tuesday night SSB net about me running 10KW...

You do always come through very clearly to my QTH.

that shows on 9.25 KW not 10,000

so I dont believe you.

You have one of the cleanest signals I have heard. It's nice when someone runs power, and are courteous enough to set up a clean system. It sucks when some jackwagon is running a KW, and making 6khz unusable for everyone else.

So, what IS your setup?

Thanks! I make sure the audio settings are correct and compression is not to much, plus I make sure to have plenty of headroom on the amps.  Example the SB 220 is capable of 1800+watts into a dummy load with 100 watts drive, I run it at legal limit with 80 watts drive.

It's close enough to 10KW for who it's for!

It depends on what's inline, it's either a modded SB220, Mercury III, or a modded AL-1500.  On the low bands the antenna is a ladder line fed doublet @ 28'.

Leaving aside the mostly horrendous IMD performance of amateur radio amplifiers in general, it's easy to get a clean signal: Don't Overdrive Your Amplifier.

Don't drive your amplifier into saturation. In fact don't drive your amplifier past the P1dB compression point. When you go past the P1dB point or, worse, into saturation, that's when you get horrible IMD (intermodulation distortion, aka "splatter") because the "linear" amplifier is no longer operating in the linear gain range.

Almost nobody operates this way, though. Billy Bob bought his legal limit, 1500W amplifier and, damn it, Billy Bob is going to get his money's worth! If Billy Bob doesn't see the 1500W indication on his power meter at least 80% of the time he thinks he's got to turn up his drive.

The reality is that the crest factor, aka peak-to-average power ratio (PAPR) of compressed human speech is typically around 6dB (uncompressed is about 12dB but does any ham not use their speech compressor?) Hence most of the time the amp should be averaging right around 1/4 of it's power output. Billy Bob can't ever abide his 1500W amp only showing, say, 400, or even 800, Watts. The reality, of course, is that his amp is reaching 1500W on peaks but the relatively slow power meter isn't showing those peaks. Indeed, even so-called peak reading power meters (even an expensive LP700) aren't fast enough. The only thing fast enough is an oscilloscope.

Do your compression in the audio processing, not in the amp. Set your amp RF drive level using the tune or CW function of your radio. Using that pure tone, set the drive so that the power meter is showing the maximum output of the amp. Then adjust your audio drive (mic) level so that the amp only shows around half that most of the time, with rare peaks up to the maximum output of the amp. Without an oscilloscope station monitor, figuring out what "most" and "rare" means is somewhat subjective, of course. But remember that by giving up at most a half an S-unit you get a much cleaner, nicer sounding signal, even with high audio compression levels. Rare DX stations will often answer someone who sounds great vs. those who sound loudest.

I bought a Xiegu amp to go with my G90 in the shack. They have an alc interface that works very well. When doing digital, it will drop the power from the radio on some bands to less than a watt, and push out 75 to 80w with the alc level at zero. It depends on how resonant the antenna is as to how much in and out is used. I can kind of "force" it to push out the full 100w, but it really doesn't make that much difference in who will hear me, and just puts out a crappier signal.

In the land of the 3.898 Horserace crowd, that would be considered low power.

His call escapes me but the late Zach Reynolds (of the RJR Tobacco family) was popped running 27KW. And a few who knew that crowd stated there were bigger amps yet.

I guess if you can afford a station like that, you can afford the fines.

Good grief. That's a lot of power. I wonder at some point if power can overcome propagation.

Good on the air friend of mine always says "Running 700 Watts here..." Come to find out it's all a joke, he's really running 7KW! I've seen photos of the amp More seriously, it's a homebuilt work of art!

Same dude is running a shunt fed tower on 160M. And, even though he's an Extra, still rocks a 2x3 call. And is so mellifluous he could easily get a job doing voice work. Truly a renaissance man!

And then you hear XX2XXX/QRP get picked up by the DX station.

lol. Yeah those crack me up.

Plenty of headroom is nice to have! And at least a legal limit amount of headroom is even better.  

Just poking around on ebay, it looks like there are a bunch of LDMOS amp kits available in various wattage, with or without the transistors.  There is a place in Greece that sells the boards along with a lot of other necessary modules like LPF boards, radio interfaces, T/R switching modules, etc.

It's tempting to look at the relatively low prices for the boards, but when you consider having to source an enclosure and power supply, and all the other stuff, plus to time to assemble it and get it figured out, it might be worth paying double for a commercially available amp with a warranty.

I sure wish I had the time and money to build one, but the way I end up with projects like these is I'd end up spending more than an off the shelf amp just buying crap I need to put it together.

I've had that exact conversation with myself

Mercury IIIs is still a good value.  Not a kit anymore as it comes assembled and tested and with a great warranty. The waiting period sucks, but the demand is just so high. Mine will be 4 years old in December and has hard prolonged usage. So far so good.

Check out VK Amps. They have some very nice kits. I am going to go that route. I already have a 50v supply for my 2 harris amps so that is a big part  of the puzzle there.

Yeah good thing it's a hobby, otherwise none of the expenses so far would be justified.

They have some nice stuff.  Looks like they sell a full kit, just add power supply, heat sink and enclosure.  I didn't see a stand-alone amplifier board.  They sell a splitter/combiner that would be nice to add to their kit along with a second amp board.

Their power supply doesn't look like it could support 2 amp modules though.

I did see someone had built one of the ebay amps into a computer enclosure, which seems like a decent cheap option.

I have a couple large audio amplifiers that are dead that I could scavenge a case and heat sinks from... assuming a 2U rack case would be big enough. Still seems a bit spendy for a partial kit, especially one that's not legal limit.

Yeah that's the issue.

I'd pay $2k at the upper end for everything I needed to construct a legal limit amp if I had to build it myself and get no warranty.  That's for a well designed kit with pre-punched holes in the cabinet, heat sinks, power supply, toroids wound and boards populated, with well illustrated and comprehensive assembly instructions.

Because for less than double that I can get an assembled, functioning amp delivered to my door that will do legal limit and comes with a warranty (a tube amp, but still).

DIY only makes financial sense if the time and effort you put into it doesn't offset the savings.  Sometimes if you really enjoy building stuff, breaking even or being in the hole a little doesn't matter.  

It seems like what you're paying for here is the ability to get most of the components in the same place.

I am that way about a lot of smaller projects, but when you get up over a thousand dollars give or take, pragmatism starts to kick in real hard for me.