On Thu, 20 Nov 2008 00:23:59 -0500, Gary Smith wrote:
>according to the 425 30 W drive gets me 900W out I have an extra pair
>of tubes that were tested as full output and I've seen no difference
>between the two pairs so I'm guessing on this amp 30W in = 900W out.
By "according to the 425" I assume that you're either reading the meter
or the bar graph. Both are calibrated by internal pots. The calibration
could be off. I suggest you check that calibration against a known good
wattmeter.
I don't consider myself an expert on power tubes, but in my limited
experience with the 3CX800A7s in these amps, if you don't encounter
creeping grid current when you push them, they're OK. I suspect others
can provide more (and perhaps contrary) advice.
The suggestion that something may have changed value in the input circuit
certainly has merit. But before I went diving into the amp, I'd find a
reliable wattmeter and do that power calibration. In my experience, 2:1
is not a lot of mismatch. I regularly see 1.5 or more. I would only get
concerned if the exciter started getting unhappy.
73,
Jim K9YC
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