In a solid state PA, one has limited voltage swing to begin with.
Operating at 12 volts instead of 13.8 takes away nearly two volts of
that swing that was probably only 10 to begin with. Can drop the
available power by that change squared. So the output power drops (since
the impedance matching is fixed by the output transformer) by 8/10
squared dropping full power to 64% power. The peak currents try to be
the same but don't make it. The ALC tries to let the radio do full power
so lets the drive be high and cause splatter.
Some voltage regulator circuits (Scout for one) require more than 12
volts to regulate. Likely there's a 10 volt regulator for some critical
circuits that requires 2.5 volts minimum overhead to maintain
regulation. I know when my dad's battery voltage gets low, the first
sign of low voltage from his TS-440 output (besides loss of output
power) is that his voice begins to sound raspy. At the extreme his
bandwidth increases to about 20 KHz.
Where radios were designed for 117 volts and have 125 volts applied,
tube and lamp life can be shortened. A variac or bucking transformer can
correct the excessive line voltage (if the utility won't correct it) to
extend equipment life. Without a bucking transformer for the whole house
one should purchase 125 or 130 volt rated lamps instead of the common
120 or 115 volt rated lamps for a far greater lamp life. 5% change in
lamp voltage causes a doubling or halving of lamp life, depending on the
direction of change. I have found 130 volt lamps at Dollar General for
reasonable prices. 13.8 volt power supplies generally used for ham gear
regulate the output voltage independent of the line voltage.
73, Jerry, K0CQ
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