One possible issue with the 4-400A is that it has a metal shield around
the glass seals on the base.
The cross flow cooling used in some amplifiers does not work well and an
additional fan
may be need to cool the seals.
Maybe someone can comment on this that have had personal experience
making the conversion.
73
Bill wa4lav
At 04:20 PM 12/4/2011 -0500, John King wrote:
>I have several very good 4-400 A tubes and have replaced a pair of bad
>3-500Z tubes with a pair of 4-400A tubes in a Heath SB 220 amp.
>
>I have noticed much lower resting current being drawn when keyed up. I
>have noticed about 200 watts less power output with 100 watts drive. The
>4-400A tubes are as new.
>
>I made no changes to bias or other parameter adjustment. I would
>appreciate the benefit of your knowledge and experience regarding the tube
>substitution. Thanks and 73, John, K5PGW
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