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[AMPS] 4CX1000A advice??

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Subject: [AMPS] 4CX1000A advice??
From: (Larry Molitor)
Date: Fri, 13 Mar 1998 04:54:14 +0000
    Over the Last thiry years or so, I have designed and/or built literally
dozens of power amps, both at home and on the job. These span the range of
audio thru L-band, from a pair of 1625's (??) to a multi-KW L-band solid
state job. Of all of these, my 4CX1000A amp has given me the most grief.
It's been over ten years since the last time I rebuilt it, so I thought it
might be fun to do it again. (Sure!)

    I have been going thru the last several months of list archives looking
for clues, hints, revelations, etc, for passive grid tetrode amps hoping
that I might find something that I overlooked in past design efforts. I am
amazed at the amount of knowledge and experience (and EGO) possesed by the
list members in general. In spite of this, I could not find answers to two
points that are currently bothering me. 

    First question: Many references have been made to grid damage in the
4CX1000A and similar tubes; what are the detailed symptoms of said damage?
(Assuming the tube still sorta operates)

    #2: I want to include NFB cathode resistance this time around. Looking
at the Measures' and Daughters' versions, I see no mention of filament
chokes. With the cathode either connected to the filament at the factory
(4CX1000A) or by preference (4CX1600), I don't see how this can work. The
filament is either bypassed with caps or thru the filament transformer
windings and therefore the cathode resistance is bypassed as well. Am I
missing something here? If a filament choke is required as I suspect, then
that is yet another reason why one should never consider a tetrode for a HF
amp unless one gets one with handles for FREE!

   Help me out here guys. I know lots of you have been there and done
that.... show me your T-shirts!

Thanks es 73,

Larry - W7IUV

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