Guys,
Thanks all for your responses, lots of food for thought. I think the GU5b will not do what I need/want. It will need 100w drive for about 1kw output, so not enough gain.? The gs35b suggested here and by someone else looks like a great triode as an option. 100w drive should easily produce 1.5kw output.? The filament is easy to deal with too etc. it's not expensive which is another bonus. So let's call that option 1.
Option 2 then, is more complex. A tetrode. Sure I was initially put off with the extra circuits required, but after reading some more and looking at f1grv's site, they look good. He supplies the control and protection boards, so that makes life much more easy. He is suggesting for upto 1.5kw with 100w drive use a triode like the gs35, or for real power, over 2kw, use a tetrode. His tube of choice is the gu78b which he says is happy at 3kw, and can be pushed to 5kw, which is more than I need or want. Also that tube is expensive and less available.?
So I was thinking a gu43b, which is very "cheap" at about 100 bucks, very available,, easily filament supply, and can easily do 1.5kw output. Can even be pushed to 2kw, which was/is? my original goal. But what about running a pair, for 2kw all day, with 3+kw peak ssb..? I have the anode supply capacity..? Oh boy. Down the rabbit hole i go.?
Thoughts. Cheers guys.?
