UNCLASSIFIED
Gents,
I have built a GG linear using a pair of 4-400s. The circuit is similar
to the ARRL 'junk-box' linear of 1983.
My problem is that I only get about 500 watts out; CW or pep, no matter
how hard I drive it (measured on a Palstar PM-2000).
This power output is with two tubes, or one in either socket. I have
tried combinations of 4-400s and Philips 3.5-750s with no improvement.
I get this with about 35 watts in, and using an LDG tuner on the input
form the exciter (0.5 metre length of co-ax to input from tuner)
Also, this output is only available on 160, 80, 40, 30, but I cannot get
any output on 20 or 15! (only the input drive appears at the output, no
tune and load dips!).
this, no matter what tapping I try on the tank coil.
The HT is rock solid at 3.8kV (big 3kVA transformer, full wave
rectifier, and 25 uF smoothing), and only varies about 100 volts when
driven to 500 watts out, idling current is about 120 mA. Heaters are
good at 5.0 volts at the pins).
I did a frequency sweep on the input circuit and it is flat 1-30 MHz.
The amp seems very stable at the available output power.
I get the impression that the amp has too much effective capacitance at
the input and is acting like a LPF and rolling off beyond 10 MHz. But
why?
Can you Guys suggest anything I could do for further elucidation of this
problem.
Cheers from Oz
Mike Wood VK5SF
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