[R-390] R390 NON A IF deck mods

[Shoppa, Tim]

> V508 normally a 5749 (6BA6) has been replaced with a 6AU6 ???
> Seems to reduce the IF deck gain BUT makes the S-meter zero pot MUCH
> easier to set !!
> Anyone know if this is a "real" SB type mod or just a field tech hack ??
> After resetting the IF deck pots I can't tell any difference in performance.

Almost any of the 7-pin pentodes will sub for any of the other 7-pin pentodes
in a pinch.

I posted to this list several years ago where I just started swapping 6AU6,
6CL6, 6AH6, 6AG5, 6BC5 in at random and the radio kept "working". Also sticking
these in the 6AK5 sockets (Which may not technically be the same pinout but is
close enough in typical usage) and it kept on "working" too.

The AGC characteristics are not at all identical though especially if more than
one tube is subbed out. That's what "remote" vs "semiremote" vs "sharp" cutoff
is all about.

This is in essence what you noticed as you noticed the zero pot sensitivity changing.
The AGC curve of the radio was shifted. Change more than one tube out and AGC
instead of "still mostly working" will start working more obviously wrong.

Tim N3QE