[ARC5] nbfm detector (6BN6 - a good valve)

[Ian Wilson]

Hi Les,

Thank you for a very interesting reply and some good reading.

The comment about high gain not necessarily being a good thing is
interesting.
This supports the ancient wisdom that triodes make better regen detcetors
than
pentodes, and that tubes make better regenerators than solid-state devices.

My own take on this is that it's the second derivative (of effective plate
current
versus control voltage) that determines how well-behaved a regen detector is
as
we approach regeneration. Triodes have nice gentle curves and a low second
derivative. Pentodes have much sharper gm curves hence are less
well-behaved.

The 6BN6 would be unique as a regen detector because the part that would
function at RF (control grid, accelerator) operates at fairly low gain and
high
currents. Only the target/plate operates at low current.. The gm of the
device is
not very high; only the conversion gain is, because a 300k plate load can be
used with a 250V supply rail.

It may be that the 6BN6's susceptibility to microphonics and stray magnetic
fields kills it as a regen detector, but it's at the top of my list of
things to try next
time I stray away from superhets :)

73, ian K3IMW