Andre Jute wrote:

I gave up the idea of direct tube drive of Quad ESL63 years ago as too
hot and too dangerous. But my recent experiences with Stax
electrostatic earphones driven by small OTL tube amps makes me wonder
if the next breakthrough in tube amps will not be a combination set of
a tube amp directly driving the associated fullsize electrostatic
fullrange speaker.

A full range ESL does require a large voltage swing.

Quad ESL57 have a 300:1 step up ratio tranny and so if 25Vrms is needed
at the low voltage input coil, then without the tranny
the voltage required is 7,500Vrms.

Where does one get a linear 7,500Vrms from?

ESL63 and later derivatives are slightly easier to drive, but basically
the drive voltage needed isn't ever going to become lower because of the
laws of physics
with regard to charged plates, the distance between them, membrane
travel requirements,
and high voltage Vdc charge biasing.

Its all OK in a pair of ESL headphones because the levels of Vac drive
and bias etc are
all far lower than the potentially lethal levels in a full size ESL
which has to fill a room with sound, not just an ear held close.


Morgan Jones explains how he uses a pair of PP 845 to get a high drive
Vac.
Many other tubes capable come to mind, 813 operating off several kV
perhaps but they will never ever
be adopted by anyone except the few clever types who enjoy doing things
the hard way.
Radio amateurs routinely ran their transmitters with several kV but it
takes
huge dedication to be a really capable radio amateur if one builds
each and every part of one's own radio station.
DIY with HV to get better audio than available by other means is also a
challenge.

I don't mind using magnetism as the means to get from tubes to ESL
panels.

Patrick Turner





Andre Jute
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