[HBR] detector /agc

[Walt Hutchens]

Don posted:
> -New to the list!  I am looking for any thoughts on the 'best' infinate Z
> detector.....I am looking at the 12at7 as used in the hbr13c....I plan to
> use a 6cw4.  Trying to get the cathode bias just right for proper
> cutt-off.....I am runing about 104v on the plate....any thoughts?

Did this truly get NO answer?  Or am I missing some posts?

The infinite impedance detector isn't a critical circuit. As I recall
the Handbook circuits show parts values and either give a list of
various tubes that will work or don't mention the tube type at all.

Basically when using a new tube type in this circuit you can just wire
it up with whatever cathode resistor value is recommended for the
other tubes and check to be sure it works okay.  The voltage gain is
nearly one for all such circuits and about the only other problem you
could get into is noise and an unstable operating point if you got the
cathode current way too low.  The optimum is very broad.

That's one of the great advantages of inf. impedance: There's no trick
to getting it to work. (Standard W6TC design philosophy!) I tend to use
plate detectors but tinkering is generally needed to get good
linearity with those.

I don't like to use tubes that will oscillate at 1000 Mcs (like the
6CW4) in MF/HF/audio circuits because I always suspect them of
secretly wanting to oscillate regardless of my intent. (I've had
enough trouble with 12AT7s!) However, if the plate RF ground is short
(and to the same point as the cathode bypass), it probably will be
okay.

Walt
KJ4KV