Frank, thanks for starting this thread! (and, yes I read it all)
Enjoy your new rig!!

(and with the clean AL-800H, not needing 100-watts of drive, so being driven with the 7610 at reduced power, I'm assuming you'll have a nice clean signal!! Congrats!!)
{And, I appreciate Brian, K6BRN's detailed explanations of ham SDR's....I sent that to a couple friends, cuz you explained it better than I could've....btw, my first exposure to SDR was from a old friend hired to do test/eval of the SDR radios in the B2 Stealth Bomber, that was like 17 years ago, and he couldn't tell me the details, but wow...}
I don't have an SDR / direct-sampling / DSP rig, and since I really like radios with knobs (old school, I know) it's doubtful that I will buy a black-box SDR, but have been considering other options....just wish the 7610 had active pre-distortion, or that ANAN would make a radio with knobs...
As some may know, I was thinking of upgrading / spending $$$$ on a new rig....but when I went looking, I found few had as good of transmit spectral purity / transmit IMD as my older legacy rig, and none came close to my maritime HF rig that I primarily use these days...
But, I'm still considering things...

I'm not Zenki....and I'm not throwing any IMD grenades...
Just wanted to say that I've been reading this thread a while now, and I wanted to point some of you to some actual transmitter test results that might be helpful...
And, yes, while the TS-990s (with its $7000 price tag) does have a fairly decent transmitter, and certainly better than most modern ham rigs, even it is not that stellar....nor, in my opinion, is it like Ed (VE3WGO) said "fantastic"....
But...
But, let's not deal with opinion....let's look at some facts....
Fact is, while higher-voltage SS PA's allow the devices to operate longer in the linear part of their cycle, simply having a "50-volt PA" in your ham rig is not
the determining factor to having a clean, linear transmitter with lower transmit IMD products....it can help the designer make the PA cheaper while maintaining its linearity, but fact is there ARE current production HF ham rigs (and HF maritime rigs) with 12-vdc PA's (TS-590SG, etc.) that have better transmit IMD than some with 50-vdc PA's (like the 7800, FTdx-5000 etc.)
Please have a look at the ARRL test results....and you can see this...
https://www.eham.net/ehamforum/smf/index.php/topic,97093.105.htmlEd, VE3WGO, I'm not nit-picking here....and please know this is not about you...just that you posted this here, so...

Please let me know where you found the Kenwood TS-990 test data that showed
"3rd order IMD at -40 dBc"...as that would be -46db (PEP)

The ARRL Product Review Test showed a best case of -39db (PEP), and worst case of -31db (PEP)....that's 7db to 15db worse than the test results you provided...
Here are the 3rd, 5th, 7th, and 9th order transmit IMD from ARRL product Review Tests....please note these are db(PEP), not dbc...
Kenwood TS-990 (50vdc PA)
-31 / -46 / -52 / -57 (worst case)
-39 / -46 / -54 / -56 (typical)
And, for this discussion's comparison, here are the 12volt PA TS-590SG and Icom IC-7300...
Icom IC-7300 (12vdc PA)
-30 / -37 / -44 / -58
Kenwood TS-590SG (12vdc PA)
-31 / -38 / -48 / -55 (worst case)
-42 / -38 / -48 / -58 (typical)
Les, there's no way that the IC-7300 Tx is on par with the TS-990. Your TS-990 has a very linear 200 Watt transmitter. 3rd order IMD at -40 dBc. Fantastic result due to its high voltage FET power amplifier.
But if you and others think both these radios' transmitters are on par, then Kenwood's effort to make a superior Tx in the 990 was apparently all for naught.
73, Ed
My fellow hams considering spending money on a new rig (as I have been think about doing as well), may wish to actually place some concern into the transmitter and its spectral purity....and actual test results of these transmitters....
And, in particular, please take note that with typical human speech, the "3rd order IMD products" of our SSB transmitters can fall within the transmit passband, or very close to / just outside of the transmit passband edges, and much (except for those with "boosted" bass response transmitters/audio chains) of the immediate adjacent frequency splatter is coming from the 5th order products, with the higher order products causing splatter up/down a few more khz away (sometimes as far as +/- 10 to 12khz away!)...so, while the marketing guys hope all you look at is the 3rd order products, fact is if you desire to improve the airwaves / reduce the splatter on-the-air you should be looking at all the IMD products, especially the higher order products....(oh, and turn down your mic gain, too...)
Please have a look at these pages....the actual facts are there...you can read/analyze them yourself, and make your own choices of rig as you desire....(but, if my fellow hams don't have the facts, most are making uninformed / poorly-informed decisions)
https://www.eham.net/ehamforum/smf/index.php/topic,97093.msg1053647.html#msg1053647https://www.eham.net/ehamforum/smf/index.php/topic,97093.255.htmlIt surprises many that the "12volt PA" TS-590SG has a 2db to 3db better 3rd order and 9th order transmit IMD than the "50-volt PA" TS-990S....with the 590SG about 6 to 8db worse on its 5th and 7th order products....(this is primarily due to the design and tuning of each of these PA's....in that they could be designed/tuning slightly differently and one might produce better lower-order products at a sacrifice for higher-order products, and vice-versa...btw, this is explained in detail in posts, by me and others, in that other thread I reference..) Not to mention being better than the 50-volt PA IC-7800 and FTdx-5000!!
And, some might find the actual spectral scans showing a direct comparison (on the same screen) of a "modern" rig (IC-7600) versus a "legacy" rig (IC-756ProIII), to be helpful...as well as the old FT-1000 MkV in Class A, versus a K3...
Have a look:
https://www.eham.net/ehamforum/smf/index.php/topic,97093.msg1080308.html#msg1080308Anyway, I really just wanted to point out a few things:
a) There is a
lot more to what makes a great rig than where it is on Rob's list (and if you don't believe me, why not click on the links I provided and read Rob, NC0B's own words...)
b) It is a myth that just using a rig that has "50-volt PA" means you necessarily have a clean transmitter...
c) We hams are getting shafted these days by the slip-shod / half-assed engineering of the transmitters (primarily the PA's) of our modern rigs, and as such the limiting factor in our
receivers is not our receiver specs, but rather the transmitter specs / transmit IMD of
the other transmitters on-the-air (typically within +/- 20khz to 30khz of you)....and this has been the case now for a long time (a decade or two), and many of the same guys who strived to bring us clean receivers with high dynamic range (NC0B, W6XX, K3LR, W8JI, etc.) have been saying this now for years/decades!!!
Please read what they have written...
(heck Rob, NC0B started talking about this in the mid/late 1970's....from Dec '77, when writing about SSB operations:
"Generally speaking, transmitted IMD from an RF power amplifier [transmitter] will be worse than that internally generated in the receiver, with the result that the transmitted IMD may cover up a receiver's shortcomings." as well as many times since then has gone into great detail about how our own transmitters prevent anyone from ever using the best of our receivers' capabilities these days...)
Oh, and one last point...please remember these IMD products are distortion products that are outside your transmit passband / outside the filter bandwidths, and as such cannot be "heard" by anyone listening to you, they must tune up/down to hear / monitor them (or they can use a spec analyzer, to see them)....so, anyone that thinks because you get complimented on "clean audio", etc., that this means you are transmitting a clean signal, please understand it does not...
(now, while really harsh and distorted audio can be an indication of an over-driven rig / too high mic gain, etc....and these can, of course, cause poor transmit IMD, so can a poorly designed PA, improperly adjusted ALC, poor voltage regulation, over-driven PA, even poor swr with SSPA's, etc. etc...and none of these can be "heard" on your frequency...)
Also, please note that there are no transmit IMD specs/rules for the amateur radio service....not FCC, not EU, UK, etc...it is up to the operator to assure that they are using the minimum bandwidth necessary for the mode of operation and to assure they are not interfering with any other stations....
We should all remember that the manufacturers do not have any IMD spec to meet, other than what we hams are willing to be BS'ed into swallowing!!

Okay, no long rants about IMD today....just trying to provide you all with some links to some actual test results...
So, I will close with what I reopened the other thread with, back in February:
I suppose that since most never hear themselves on-the-air, and darn few ever hear what their own transmitter does on freqs +/- a few khz (or worse +/- 10 to 20khz), the actual transmit IMD and spectral purity of our signals tend to get over-looked...and that is a shame!
73,
John, KA4WJA