Welcome to the Second Plasma Tweeter Zone
Get ready for the plasma midrange, it's coming
in early 2002! It will use the 375 watt 813
transmitter tube, and a 2kV power supply (see the high voltage capacitor
array-- rated to store 320 Joules)!
- This is now my second set of plasma tweeters that I have
constructed. This set, called the Plasmatone-RG1's was a commissioned
set that I started in June 2000. There have been many ups and downs, but
they are finally near completion. The main difference from the old set is that they incorporate a vacuum tube
preamplification stage in addition to the normal stage. They also use a
high quality, quiet 120vac fan, and each tweeter has it's own 250VA power
supply. If I had to do it again (please no! I already had to tear the
preamp board apart and rebuild it once!), I would have separated the power
supplies from the tweeter cases, because I had a difficult time with
power supply noise. The coils (see below) are wound with 16-ga magnet
wire this time instead of 18-ga. I bought some 3" tea sieves at
Lechter's Housewares for ~$5 each with I used as mini Faraday cages
around the flame. The tea sieves did not take to solder, so I had to
"sew" them to the copper rods with copper wire, which I then soldered
to the rods. The housing for these tweeters is a Hammond steel cage
with the corresponding aluminum cover plate acting as the bottom.
Normally, there is a 2" steel chassis between the plate and cage,
but I went without that, which made the parts mounting more difficult,
but saved some space.
- I know several people have emailed me to get the schematic for this
device. I just finished the schematics for the RG1's as I have
This may not have been the best possible circuit, so I encourage the tube
gurus out there to design a better preamp circuit, better grounding,
better power supply -- but these work and they work well! I think the best
recommendation I could give would be to use a full-wave rectification on
the power supply, since my half-wave causes some 60-Hz noise. The
are essentially the same as Ulrich's except I removed the BF869 transistor
and replaced it with a 12AX7. The gain, which wasn't high enough before, is
now even lower! I have been running them out of the 16-ohm tap on the
Dynaco st70 that powers my Voigt Pipes, but I
would recommend using two 12AX7's and have put
a schematic together for that too here,
although it has not been tested. Tubes
are very easy to use because there is a +300 volt power supply available.
An alternitive would be to just use two BF869's together capacitively
coupled. Just remember that the BF869's generate enough heat to want a
small heat sink (or use the chassis as a heat sink, but make sure you
isolate it electrically!).
- Here's a picture of Bernhard's Plasma Tweeter, which looks very
A view of the tweeters with the bottom covers removed. The power
transformers are visible on the left in the case. The preamp board and
12AX7 preamp tube are visible in the front. The controls are visible on
the rear of the case.
The two tweeters set up for demo. The non-directional stereo effect
created is unbelievable. No matter where you stand, you get the same
frequency response. Regular tweeters only give good frequency reponse
on-axis, so the stereo image is distorted if you step off-axis.
A view of one of the tweeters complete with engraved name plate
(under the coil).
This is the coil I used on these tweeters. I wound thread around each
turn of the coil. 4 of the theadings are basically perpendicular to the
direction of the coil winding and the other 4 are diagonal. The coil is
15 turns of 16-ga. magnet wire wound on a 1.2" diameter air core. The
turns have a little bit of air space between each winding to keep
These schematics can be improved upon! Here is a recommended configuration
for higher voltage gain. I have not done any load-line analysis on the
dual tube version, but I think it'll work fine (not optimal).