I hope I can get some help on this nagging problem. I have an RCA SBA-1K
amp, a pair of 3-400Z's G-G, running about 2800 VDC on the plates (yes I
know they are loafing!). My problem is this: I can develop about 400 watts
out with 50 watts of drive but only 500 watts out with 100 watts drive. I
don't have any Ip reading, (the amp measures only cathode and grid current,
output current was measured with a RF ammeter but that got "zorched" when
moisture developed inside the meter casing!). I have switched the tubes, (I
started out first with Sylvania 8163's then switched Amperex) with no change
of symptoms. Any ideas??
Thanks,
Mike
W3SLK
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