Have had some good suggestions and have followed same:
Have switched to 220V and adjusted tuned input on 15M to indicate
a 1:1 SWR between the Yaesu 757 and the AL-80 (it is 1:1 across the
entire 15 meter band, now). The tuned input adjustment helped the most. I
gained 100-200 watts altogether. Get 500-600 out on 15 with about 50-60
drive. Grid current is a little higher than what is called for but seems to
be close to what it should be.
But - get this - I can go ahead and increase drive to about 90 watts on 15
meters and get 900 out. In that configuration, the plate current is a bout
625 and plate voltage about 2200 (input therefore 1375 W - not counting 90w
drive) which gives about 65% efficiency. Grid current in that configuration
is 400ma. And, of course, plate dissipation works out to 475W (or 565 with
the 90 w drive included, right?). Now, according to the manual, grid
current in excess of 150ma in CW mode indicates excessive drive or improper
loading.
My questions then are: Other than shortened tube life, what is wrong with
excessive drive in this situation?
Second, how can there be improper loading - it looks to me like it loaded up
just fine.
Another note - when I switch to sideband and look at the output on the scope
it looks very nice. I usually use the word "five" to get a nice pattern to
examine and the rf source is that radiated from the antenna. I am not using
the ALC, yet, but the grid current on the meter as I speak on ssb averages
around
75-100ma (occasional peaks over 100ma).
Other note/question:
I can't get the SWR down below 2.5:1 (between xcvr and amp) on 80M. Also, I
am maxing out the capacitance on the load control on 80 (probably 40 and
160, too). Also, am using way more capacitance on the load control all
bands that I have tried (including 15M). The tube in this thing is an RF
Parts 3-500ZG. So far I've not found a data sheet for that tube and wonder
if its specs are enough different from the 500Z that input and output
impedances are somewhat different. Enough to cause some of this.
Temporarily - while testing only - this amp is grounded via coax braid to
transceiver and to dummy load to good earth ground (not good but wanted
to mention that).
73, Lu K5YP
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