[Heathkit] HR-10 and the grid stopper

[Forbes, Doug]

I received enough private e-mails to lead me to believe there is some
interest in what a grid stopper is so I am posting this to the group.

Well a grid stopper is a kind of cheat. It can also be used with MOSFETs.
The idea is to form a low pass filter using the capacitance of the grid (or
the gate in the case of the MOSFET) and a series resistance. The resistor
gets installed as close to the grid connection as possible so there is no
chance of the lead from the resistor to the grid picking up any unwanted RF.
It's used a lot in audio as well. Any time you have a lot of gain and a
relatively wide bandwidth (as you do with tubes) you have potential problems
and even though you bypass everything and make it as tough as possible for
the RF to get in sometimes it still does. The grid stopper is one way of
handling the problem without sacrificing the gain of the stage. 

Doug Forbes WA67VYN
Professor
Computer Science,
Music Technology
College of the Canyons
Valencia, Ca.