"flipper" wrote in message
...
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?

What's the goal? To 'fix' a broken radio? Why not just buy the proper
valve and plug it in?

To some extent its just a bit of fun.

One significant inconvenience is that most UK radios had series heater
chains, so a dropper resistor would have to be wired in to replace the
valve's heater.