QUESTIONS & ANSWERS
■ FIGURE 4
tubes should be operated push-pull,
class AB, for reasonable power
output and low distortion. I have
modified your design in Figure 5. The
final stage is AC coupled because
there is no point in maintaining DC
coupling, and it would be difficult.
The first stage gain is about 60
( 6.8K/110), but the second stage is
just a phase splitter — it has no
gain. You will need a preamp to get
the maximum power output of
seven watts. The bias current in the
final stage is arbitrary; I chose 10
mA, so you would adjust the negative
bias to obtain one volt DC at each
cathode. Matched 6V6 tubes will be
necessary. According to my tube
manual, the output transformer
should be 10KCT: eight ohms. I
have labeled the schematic with
the expected voltages and currents.
If you build it, let me know how
it works!
800 MHZ BUSINESS
BAND COMMUNICATION
QCan you tell me where I
might get a book on FM
communication decoding
and encoding? Or, maybe
at least a schematic? If it matters, it’s
for the 800 MHz business band FM. I
have been monitoring the band for
4+ years now — just a hobby.
■ FIGURE 5
August 2008 29
