[Moon] 8874 arcing

[M. Watanabe]

Dear John,

I wonder if your 8874 had an arc mark on the ceramic seal between anode and 
grid ring.
You might try to erase it with a teeth brush and teeth paste.  Pour enough 
water to wash it out,
and dry the tube enough.

But most serious problem you might encounter is interelectrode arc between 
grid and cathode.
It an event of arc on the ceramic seal between anode and grid ring happens, 
the current goes to
cathode by some way; interelectrode arc or throug grid meter shunt....  They 
are more serious
than the arc mark on the ceramic seal.

So after erasing the mark, please be very careful to put the plate voltage 
to the tube.
Interelectrode arc may happen even if the tester does not show short between 
the grid and
cathode; because of the possible internal gas which was produced during the 
arc event inside
the tube.  A certain voltage between the electrodes causes serioug shorting 
problem.  It means
nothing happens during the warming up, but it may happen when you drive the 
amplifier.


Mike  JH1KRC


----- Original Message ----- 
From: W5UWB2 at aol.com
To: moon at moonbounce.info
Sent: Friday, September 28, 2007 10:03 PM
Subject: [Moon] 8874 arcing


Gents:

My 8874 (2 meters) arced across the ceramic, grid to ground due to excessive 
dust buildup.

What is the best way to clean the ceramic in order to stop additional arcing 
along the same path?

So far alcohol and pencil erasure have not worked.

Perhaps all is lost?

73 - John W5UWB






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