Paul -
Gassy tubes don't always glow blue...... When enough cathode material
deposits itself on the grid, the grid begins to emit electrons, causing
the grid to go more positive. Called "gassy", but really "grid
emission". End result is when the grid gets hot enough to emit, the
grid goes more positive, and is no longer able to cut off plate current
with a given bias applied. Typically happens when a tube is turned on
"hard", then when the normal cutoff bias tries to turn it off, there's
not enough bias and it stays "on".
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Paul Strickland wrote:
C-145 is under attack on general principles of age. The birth
certificate shows the date of September 21, 1973. This device needs
to be replaced before it causes all sorts of problems. A gassy tube
had crossed my mind but this one still glows a nice warm orange. Past
experience is that a gassy tube will take on a slightly blue tint
around the edges. R106 sorta slipped under my radar. Forgot that
these resistors used Fullers Earth that dries out over time. Not like
these new thin/thick etched film ones we have today.
Thanks for the ideas. I will get into these and check them out. More
Later as progress to healing this ol' girl goes on.
73's
Paul Strickland
WB9SUG
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