Oh, if it's something you built anyway, you might consider using
something like an LM386 for the audio output stage. Besides providing
considerable gain (which might eliminate some other stages), it'll drive
an 8 ohm earpiece with no problem. And it's reasonably efficient.

Roy Lewallen, W7EL

Paul Burridge wrote:

I instinctively doubt it, Fred, but I'm in a position to give it a try
so I shall duly do so! I'll report back the results later.
BTW, this isn't a conventional hi-fi type audio amp; it's solely been
designed for picking up very faint, distant sounds. I was intrigued by
the design so set out to further examine how it worked. I've spiced it
and have now built it; the last piece in the jigsaw is the Z-matching
problem.