[R-390] 6C4

[David Wise]

It definitely won't smoke, but while the 6F8 and 6C8 are
both dual triodes, with identical pinouts, they are different
mu and so on.  ISTR that the limiter side is used as a diode;
that's hard to do wrong.  The other side (2nd detector) might
give you insensitivity or distortion.  It's wired in a
so-called "infinite impedance" circuit, a cathode follower biased
near cutoff.  The positive half-cycles bring it out.
High mu is important here, and the 6F8 is a medium.  But it
will probably run well enough to keep you entertained while
you dig up a 6C8.

Dave Wise
RAO-3

PS - Want a schematic I drew up in my teens?

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Barry Hauser
> 
> I have a National RAO-2 that turned up with a slightly broken 
> 6C8G -- where 
> the "G" is probably for "glass", but could be "George", who 
> knows.  Anyhow, 
> the thing is broken at the cap - small hole let that elusive 
> vacuum escape.
> 
> I see on that tube substitution web site that the 6F8G is a 
> possible sub.