On Thu, 29 Apr 2010 16:22:59 +0100, "ian field"
wrote:
Here is a circuit that I scribbled on an odd scrap of paper that I would
like to experiment with, but unfortunately I don't have an old valve radio
to use as a testbed.
The component values that are pencilled in will doubtless need revising and
the rest by trial and error.
The plan is of course to make a MOSFET substitute for the O/P pentode in an
old valve radio, it has 3 stages to maintain its invertingness in case the
audio amplifier has a nfb loop.
Anyone care to cast a critical eye over it and predict how loud a bang it
will make?
You're making it too hard.
Just slip a 2N7000 under your 900V device (making a cascode), tie the
900V device gate to the +30V, and bias the 2N7000 as desired.
Personally I've done this where the 900V device was a toob, and, in
the cathode circuit was an NPN with an OpAmp wrapped around it ;-)
...Jim Thompson
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