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Author Topic: K7DYY Observations  (Read 766 times)
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KD1SH
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« on: April 04, 2024, 10:47:26 AM »

  Well, I finally broke down and got myself a K7DYY Super Senior, the 80/40 version, a decision I made with some trepidation, not over financial concerns but rather over concerns that it might pull me away from my interest in my own HB stuff. Little danger of that, I think, and if anything, it might just raise the bar a bit for my own projects, which isn't a bad thing. Mainly, I wanted the Super Senior for my summer rig; I just can't get into running the tube gear on sweltering July and August days anymore.
  So, first impressions:
  It's very nicely built; looking in through the rear of the enclosure reveals what looks to be a modular sort of construction, with the major assemblies each built into their own cast-aluminum boxes. Very nice work.
  The fans are a bit louder than I'd expected, but not terrible. Given the rig's high efficiency and low heat output—even when the buzzard flies far from the roost—I suspect that they could be slowed down considerably with no ill effect at all.
  The SWR protection is very sensitive: I run an excellent Heathkit roller-inductor tuner, and even when tuned for exactly 1:1, I will still get the occasional trip. The trips only occur right at key-up, though, so I'm wondering if there's more going on there than meets the eye. A beep or a bright flashing LED might be nice to warn of a trip, since I'm usually not right in front of the rig, and the small "High SWR" text that flashes on the little LCD doesn't grab my attention. But, as Steve very helpfully pointed out, the REA mod monitor has a "beep on carrier loss" setting.
  The first time I had it on the air, I was getting notable distortion, sounding very much like RF getting into the audio, which I thought was odd, since I was using the very same audio-chain—DBX286S and Inovonics 223—that I use with my DX60 with no RF issues at all. My audio/PTT setup includes a switching/junction box, and I went in and installed bypass caps on all the switching signal lines, an RF choke in the audio circuit, and then shotgunned the whole audio chain with snap-on ferrites. No more RF on the audio.
  As far as audio quality, everyone says that it sounds very much like my DX60, with the WA1QIX mods, which is pretty much what I expected, since both rigs have a wide frequency response, and I'm using the same audio chain.
  Finally, it's not a "full legal" transmitter. I'm not accusing Bruce of false advertising, but as it comes out of the box it will not output 1500 watts PEP. What I found is that, if the carrier is adjusted to much over 300 watts, the modulation percentage rolls back to around 80%, both negative and positive, no matter how much audio you put into it. At 300 watts of carrier, I can get a nicely symmetrical 100%, but above that, the internal limiter kicks in. Bruce is very forthcoming if you ask him for advice, and he told me that he does indeed set that limiter for around 1300 watts PEP, and that there's a pot, which is shown on the schematic, to adjust that. He seems to be very conservative in his design approach; making the valid assumption that many operators will be using the rig without an effective hard limiter. In my case, with the Inovonics 223, I'm confident that I could tweak the pot a bit and give myself a bit more headroom, but I see little justification for the risk. If I were sitting on a big pile of FQPF11N40's, maybe, but really, for an extra smidge of RF that no one would notice, why bother?
    Overall, a very nice little summertime rig, or a backup rig for your big iron. No buyer's remorse here, at least not yet anyway; time will tell about the reliability.
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W1DAN
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« Reply #1 on: April 04, 2024, 12:20:50 PM »

Hi Bill:

Looking forward to hearing it on the air. Note that often a Super Senior will trip due to carrier pinch-off (i.e. excessive negative modulation), so make sure your modulation is not too high.

Also about 240 Watts carrier is a good spot to set the power as with +100% modulation, you are not running out of modulator headroom.

See an interesting thread here of our experiences with Peter W1ZZZ's Super Senior a few years ago:
https://amfone.net/Amforum/index.php?topic=33537.0

Yes Bruce is a good guy.

73,
Dan
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WO4K
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« Reply #2 on: April 05, 2024, 06:34:11 AM »

Janis, AB2RA has an excellent write up on the Super Senior here:
http://www.wireless-girl.com/Projects/AMTransmitters/K7DYYtransmitter.html.

Her advice on a look-ahead hard limiter for negative peaks and the need to control bandwidth is spot on, especially when on 7295. I run an Inovonics 223 to solve these issues, with negative peaks limiter set for just under 100% and bandwidth set to 5 kHz. As she says, the 223 is a poor man’s Optimod. There is also the MAX audio processor which gets good reviews when used with the Super Senior. Info on the MAX here:
https://www.internetwork.com/MAX/

The older K7DYY units have a tendency to drift up in power as it heats up. You have to watch it if you start out cold at full legal limit. Bruce devised a fix to control this issue. New Super Seniors now have this mod. Bruce will add it to older units on request.

After taming the negative peaks, bandwidth and SWR, the Super Senior is an excellent transmitter with great audio.. A whole lotta power for the buck.
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KD1SH
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« Reply #3 on: April 05, 2024, 08:42:40 AM »

  Janis's write up was instrumental in my decision to get off the fence and order the Super Senior. Lots of very good information about the transmitter there, and about the Inovonics 223 as well.
  I also have an older version of the Max here as well, but unfortunately, although the board is populated and ready to install into its enclosure, other projects horned in—as they are inclined to do in my shop—and temporarily put the Max on hold. Now that I've got the Super Senior, my interest in the Max will likely be rekindled, and I will be motivated to finish the project.
  Bruce seems have gotten the output drift under control; I haven't noticed any appreciable change in output while running the rig.

Janis, AB2RA has an excellent write up on the Super Senior here:
http://www.wireless-girl.com/Projects/AMTransmitters/K7DYYtransmitter.html.

Her advice on a look-ahead hard limiter for negative peaks and the need to control bandwidth is spot on, especially when on 7295. I run an Inovonics 223 to solve these issues, with negative peaks limiter set for just under 100% and bandwidth set to 5 kHz. As she says, the 223 is a poor man’s Optimod. There is also the MAX audio processor which gets good reviews when used with the Super Senior. Info on the MAX here:
https://www.internetwork.com/MAX/

The older K7DYY units have a tendency to drift up in power as it heats up. You have to watch it if you start out cold at full legal limit. Bruce devised a fix to control this issue. New Super Seniors now have this mod. Bruce will add it to older units on request.

After taming the negative peaks, bandwidth and SWR, the Super Senior is an excellent transmitter with great audio. A whole lotta power for the buck.

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"Gosh, Batman, I never knew there were no punctuation marks in alphabet soup!"
—Robin, in the 1960's Batman TV series.
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