QUESTIONS & ANSWERS
■ FIGURE 5.
tubes to drive eight ohm speakers,
but your circuit drives an 800 ohm
speaker. Where do you find a high
impedance speaker? The 10 Henry
choke allows the screen voltage to
be higher than the supply at higher
frequencies, but does little at 30 Hz.
It seems to work, though. I would like
to see some feedback, but the input
and output are in phase so you
would need to add an inverter;
perhaps a one stage preamp.
QI got my Nuts & Volts magazine and I read your eply (germanium to silicon transistor) to my question.
THANK YOU! It’s so easy to modify
a circuit ... when you know how!
I have another question. I found
the two watt stereo amplifier kit in
Figure 5 to which I’d like to add an
ultra-sensitive electret microphone
(preferably from Mouser). However, I
don’t know how and which one
would work better. The microphone
will be mounted right in the focal
point of a large metal bowl.
AAny of the Mouser electret microphones could work, but #665-POM5238PR is the most sensitive. Electret
microphones are high impedance
and don’t draw any current, so the
fact that these microphones do draw
current and have a defined
impedance tells me that there is