[Yaesu] FT-990 QRP

[Dr. Gerald N. Johnson, P.E.]

Darryl, since you are wanting to get maybe 10 watts out of the final
rated and matched for 100 watts, the voltage won't be critical for
getting 10 watts out of the 100 watt PA. If you'd tapped into the driver
stage for RF output, voltage might prove to be critical if you wish to
get all its output. Its the PA impedance match what makes most supply
voltages critical. Though there may be some low level circuit regulated
to 10 volts with a regulator that needs a minimum of 13.1 to produce the
10 volts. If you find lower voltages make it wander about or burble,
then you may not be happy with the battery voltage as it drops to 12 and
a little lower under load. Most times minimum supply voltage is critical
for getting full rated power and a little loss of voltage means a large
loss in power. There are voltage regulators in the National LM2900
family that will often plug in in place of the LM7800 and LM340 family
that can run on a half volt drop instead of the 2 or 3 that the older
chips need.

73, Jerry, K0CQ

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