This is a really fun thread.
Before WHDH went away I found a ton of unanswered letters from DXers in a file. And I found a big stack of WHDH QSL cards thanks to engineer Al Karp. So I answered them all. A lot of Scandinavian DXers. Many sent cassettes of HDH coming thru the QRM. The station gave me a lot of trouble about postage on these. So I paid the postage. (Man am I glad I don't work for the man anymore. No more arguing for weeks over pennies. I just buy what I need now. I'm going to digress here but once a salesperson brought me a script for a Bachman Turner Overdrive concert tour. I checked the library and there was no BTO CD's so I asked the salesperson to get some BTO music. He said he didn't want to spend the $14 for a CD and I should use "ANY music of any type I had" for the spot. LOL. ANY music of any type I had????? What, the Eagles? Dude, if it's a concert spot for BTO you gotta play BTO music. It's a concert spot to get people to come to see BTO. He wouldn't budge. I bought the CD myself, made the spot and went to petty cash to be reimbursed. Nope, station wouldn't pay me back. Ha. So getting them to pay for 113 envelopes going to Finland, etc., to send QSL cards "whatever they are, Jim!!!" was impossible. Those days are soooo long gone thank goodness. I've owned my own thing since 1995 and we're thriving.)
One late night in the early 1990's I made one hour boradcast DX test for AM DXers. We publicized it in advance and ran tones, morse code, Slow Scan TV of the WHDH logo, etc. We repeated the station ID very slowly in voice over and over and over picturing someone far away listening through the static crashes on their AM radio. That produced a bunch of reports from all over of people who copied the code and even the SSTV and each got QSL cards from me. I didn't have to fight hard to do put the the test on the air as excellent engineer Al Karp and Chief engineer Dana Poupolo were both hams and thought it was cool. Not a bad result for a signal so directional at night. We choose the time so it would still be dark in Western Europe and here in the States.
My best AM DX growing up on Long Island is KSL in Salt Lake, PJB on 800 from Bonaire, and Channel 3 from Tampa. Once I moved to Boston I pulled in two or three European AM stations over the years with the help of Lou Josephs from WROR. Lou and I were both correspondents for Radio Netherlands's Media Network program with Jonathan Marks and Lou really knows his stuff. When the expanded AM band first started up from 1610 to 1700 it was like shooting fish in a barrel. It must have been like DXing the Clear Channel signals in the 1930s and 40s. My best ham dx is a 2-way QSO on 6-meters using 5 watts with the Seychelles. For 60 seconds he was bombing in here in NY and I was there, too. What a catch with 5 watts into a random piece of wire...not even a proper antenna or beam.
Finally, there's the dream AM DX setup. Jonathan Marks (again from Radio Netherlands) was invited on a DX holiday to the very far north of Norway. Those guys have huts with miles of wire strung over the snow. The site is hundreds of miles from electric AC interference. He told me they tune big wonderful receivers to any broadcast band frequency, and as the earth's terminator rotates they'd hear another station waft in on that freq every few minutes from another place. They ate Reindeer (!) during the day and spent all night DXing the world on the AM broadcast band from the quietest place you can go.

Jim Cutler
major Radio geek
amateur callsign KS1A