transformers provided in the step-up boxes are mediocre at best and criminal at worst.

Subject: Easiest tube amplifier possible
   I enjoy reading the Tube CAD Journal a great deal, but wonder why a complete schematic, one that includes the power supply, and a complete parts list is not provided for the projects outlined in the journal. Take this as a question and not as a criticism (my knowledge of tube workings has easily doubled since I found your site two months ago).
William K

built both preamps, power amps and an OTL. High voltages is no limitation.
  Looking forward to see the solution of this problem from the ultimates of sound.
Bjorn

   A good starting point for anyone interested in building his own ES speaker is Roger R. Sanders book, "The Electrostatic loudspeaker Design Cookbook," Audio Amateur Press. His book does not cover any OTL circuits for use with ES speakers. In fact, in the last chapter where he gives us his wish list direct-drive amplifier for ES, he writes, "For a start an acceptable amplifier can't use vacuum tubes." Still, it is an excellent source for information on the design and principles of ES speakers.
   Building an OTL for ES requires lots of real estate, as it requires a set of large output tubes and a large power supply. Still, this path is definitely worth pursuing. I believe you will find that using triodes is the only way to go. I once built a pentode based electrostatic headphone amplifier that greatly impressed me on the test bench with no load, but disappointed me when capacitively loaded. The low rp of the triode make it a much better device to drive capacitance. No matter which circuit topology you choose, build a scaled down version first. For example, if you plan on driving 3,000 pf stators to 2000 volt peaks with 845s, build a scaled down version of the amplifier that can drive 300 pf to 200 volt peaks with a 12BH7s. Once all the bugs are worked out and the circuit is optimized, build the scaled up version. One caveat is that you will probably need much more current delivery ability than you expected.
   
                          Editor

   The short answer is that the articles cover design issues and not projects. The last thing we want is to let our readers think that there is only one way to design and build an amplifier, preamp, or crossover. The longer answer is that as you learn more and build a few projects of your own design, you will find that you can fill-in the missing parts of the schematic.  Having just said that I still see your point: having more details about a tube circuit is always welcome. Something to ponder.

Subject: Electrostatic Driver
   Thanks for a GREAT webzine! I've really enjoyed it, and I've got some ideas out of it. The amplifier for electrostatic headphones reminded me of an idea I had not long ago. Would it be possible to make a big amp for normal electrostatic speakers? My first plan was to use a pair of 813 in a totem-pole arrangement, or maybe in the circlotron configuration. A pair of
807 would probably be enough, but electrostatics need pretty high voltages to get reasonably effectiveness.
   I have no electrostatics yet, but I hope to make some. The system will probably end up with a bass horn from 25-200 Hz and electrostatics from 200 Hz an up.
  Anyway, I think this would be an interesting project. By the way, I am a real DIY, I have

<PREVIOUS

pg. 15

NEXT >