[Amps] AL1200, RTTY contesting, temps, duty cycles (not 100%)

[Kevin Normoyle]

Bill, W6WRT wrote:
"But here's the Achilles heel of the AL-1200. The low band tank coils used
undersized wire and overheated."

Thanks Bill. I've read some of your comments in the forum on the AL-1200 before. I think one of the good things we can do as users is to just document what happens in as much detail as we can. There is definitely a place for the price/performance the AL-1200 provides, and I like it a lot.

Sometimes the "complaints" about various amps lacks the detail to really assess what happened and why. It can be hard to sort out one-off issues, or generic operating environment issues.

I'm just interested in making sure I operate within the AL-1200 performance envelope. I was surprised to see all this talk about RTTY duty cycles, as if it was well defined/understood. When it seems not to be. i.e. if if was just RTTY duty cycle, do things melt on a 1 minute RTTY ragchew? I don't know, but as I described, don't care. I'm perfectly happen to limit my RTTY macros.

So part of my post is this: There is no such thing as RTTY duty cycles when you talk about RTTY contesting. There is a desirable duty cycle, but people should define it better. It's not key down forever.

And how do you characterize the difference between RTTY 50% duty cycle for two hours, versus CW duty cycle for two hours?
Does two hours matter? Why isn't a 30 minute test enough?

Now the stuff about the low band coils is important. What that says to me is that there's an airflow issue in the box. The wires are undersized for the airflow they see.

What I don't understand, is how long it took your solder to come undone in a contest? What was the ambient temp in the shack? 
Is it possible that there's a constant slow rise of temp at the coil during a contest, such that the failure needs a combination of high ambient temps, and maybe an hour or two of contesting? That doesn't seem to match what I saw, unless it's a behavior that happens at 1500W.

Hmm..I'm wondering if what I thought was temperature stability in the box after 15 minutes, isn't stable. I didn't measure the coil area. Maybe I need to? I have a hard time believing that the coil area didn't temp stabilize in my 30 minute test. No coil melted in my 30 minute CQ test at 1200W (80M) into dummy load.

Any idea what kind of antenna and SWR you had on 80M? I've not used the amp on 160m yet.

I appreciated Tom, W8JI's responses. They made sense to me. He described his use of the amp at 4000v with assisted air (outside fan) but stock blower. Although he apparently doesn't do RTTY.

I don't care about the ads. The reality in the ham world is that the users sort out what works and what doesn't and in what environment. That's the nature of the beast. Stuff that really sucks: people eventually stop buying. 

Hey BTW: in looking at other amps that people seem to like, a bunch seem to have significantly higher CFM blowers (I don't know about noise). I always wonder if a fairer comparison to the AL-1200 would be with an AL-1200 with equal CFM blower/dBA.

If you're right that it's a coil wire size issue (maybe other issues), then yeah, maybe it's not that simple. I'm musing on the higher CFM blower, maybe dialed back a bit from full speed. 

thanks,
-kevin
ke6rad