On Tue, 15 Jun 2004 10:26:39 -0700, Tim Wescott
wrote:

Barring that you could try to get your hands on someone's surplus car
stereo equipment, and harvest the power supply section from that.

Why not install a high power audio and RF amplifier in the car and
feed them from a common power supply, since you can not use those two
amplifiers simultaneously anyway :-).

Take a suitable high power audio amplifier, install a switch over
relay between the inverter and the actual audio amplifier. When the
PTT is pushed, the relay switches the power to the RF amplifier. All
the other time you can listen to the music (or to a QSO) at a high
audio volume :-).

One problem is that the RF amplifier requires a unipolar +50 Vdc
supply, while audio amplifiers usually have a bipolar supply. Running
the RF amplifier from a bipolar supply would require transformer
coupled inputs and outputs and isolation of the circuit board ground
from the chassis.

Some bridged audio amplifiers may have a unipolar power supply or it
may be possible to use only the positive side of a +/- 50 V bipolar
supply (but may require rectifiers with a higher rating).

A simple audio amplifier driven from a unipolar 50 V or +/- 25 V
bipolar supply will produce about 56 or 112 W into 4 resp. 2 ohms per
channel. In a bridged configuration 110 or 220 W into 8 resp. 4 ohms
per channel.

With a +/-50 V supply, a simple audio amplifier would produce 110, 220
or 440 W into 8, 4 resp. 2 ohms into a single channel.

I think that looking at the audio amplifier power specifications (into
various loads) should give a hint of what kind of amplifier voltages
are used and thus limit the number of candidates worth investigating.
It should be noted that even if some amplifiers are rated at 2x100 W
or 4x100 W, it is very unlikely, that the power supply is capable of
delivering more than one channel at the rated power for any prolonged
time.

The audio amplifier power supply RFI filtering may be more or less
nonexistent, so you may have to add quite a lot of filtering.

Paul OH3LWR