BATTAMP.TXT

There are a couple of schematics available for "A battery only"
powered tube (valve) amplifiers. The 3VHIFI.GIF schematic shows
a very simple single stage tube amplifier powered from a power
supply made from a filament transformer and transistor switch.
The whole thing provides maybe 50-100 mW and is powered from
3 volts (AA batteries etc).

The BATTAMP.GIF schematic shows a reasonable power (1-2 watts or
up to maybe 5 watts, depending on how you configure it) all powered
from 12 volt worth of D cells (or your car battery). It uses 6AK6
minature pentodes in the output in an "anti-ultra-linear"
configuration. I built one of these completely with 2 8" speakers
in a 12x12x19 inch box as a test of the feasibility of battery powered
guitar amplifier. As a HI-FI amp, it sounds rather nice, for its
power limitations. Distortion is only about 0.3% at a watt or so
output. Frequency respose is also good (within 0.2 dB 20-20K) at
"full" output. It uses a fixed bias output stage, with the screen
taps connected backwards from normal (provides more efficiency).

An accompanying power supply LVPS.GIF is also available on these
pages. The combination provides about 15 hours of operation from 8
alkaline D cells before the voltage drops low enough to really
become useless. (The filaments cool off when the batteries get
down to about 6V total voltage.)