Johnson Navigator Questions

Steve Harrison ko0u at OS.COM
Fri Nov 20 20:52:39 EST 1998

At 08:54 AM 11/20/98 -0600, Freeberg, Scott (STP) wrote:

>... one tunes for maximum grid current, BUT not to exceed a "grid current"
of 150 ma
>on the "plate meter".  What?   Other than not tuning for maximum grid
>current with the exciter control, there is no other way to limit grid

It means to peak the grid current but not so far as to exceed about 150 mA
of plate current. This helps to limit the plate dissipation while you are
reading the next instruction in the manual and finding the knobs to
twist/turn :o)

Actually, tubes and parts being as expensive and hard to find these days as
they are, I'd reduce that "150 mA" to something more like 100 mA or even
less. That is, start tuning the machine up real gradually, trying to never
stress anything; it'll probably last longer than otherwise.

Remember, too, that if tubes like 6146s or sweep tubes arc over internally
while tuning the machine, the plate current drawn for a moment can blow
other parts such as HV rectifiers and/of plate trahsformers. It always
pays, these days, to take it easy and slowly with these old veterans.

73, Steve Ko0U/1

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