[Amps] RF in the Audio

[Paul Christensen]

Cebik's material covers a significant amount of design and historical data
for link-coupled tuners.  W9CF, W7EL, W8JI and others have shown that
placement of a CM choke at the input of a tuner only offers a benefit when
the tuner is symmetrical.  (e.g., AG6K type, and not T, L, nor Pi types).
Specifically, W9CF writes:

"As noted by Roy Lewallen, W7EL,[2] putting a choke balun on the input of an
unbalanced tuner to drive a balanced line is useless. It introduces a
``hot'' tuner case which must be isolated with no benefit over putting the
balun on the output."

See http://fermi.la.asu.edu/w9cf/articles/balun/

Since the traditional link-coupled tuner performs the BAL-UN function across
an air core RF transformer, no CM choke is required.  The unbalanced input
side of the tuner is formed by a tapped link, and in some cases, one side of
the link is in series with a variable shunt C to ground.

Cebik's material also discusses similarities and differences between
link-coupled tuners that require the re-tapping of the output coil as well
as the output "voltage divider" tuner (e.g., Johnson Matchbox)

Paul, W9AC