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[Amps] Plate choke help.

Subject: [Amps] Plate choke help.
From: rick darwicki <>
Date: Tue, 10 Apr 2012 17:48:59 -0700 (PDT)
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Hi all,
I replaced the plate choke in an Alpha 76 with an Ameritron that is much 
bigger. First time out it arced to the nut on the back of the load cap. This is 
an older 76 with the long cap so there isn't much room.
I replaced the choke and put a piece of glass between it and the RFC and a 1/4" 
thick pice of plexiglass between the blower and the RFC. Well apparently the 
the Plexiglass lowered the resonate freq enough that it acred over to the 
blower on 20 M. I removed the plexiglass and put some corona dope on the choke 
and all seems well. I can tune to full power with 100 ma grid drive on all 
The interesting thing is on 160/24/28 at 100 ma grid current I am showing about 
900 ma plate current at max forward power, 1:1 SWR. On the other bands max 
power at 100 ma grid current is at about 600 ma plate current. It seems like 
there is a lot of RF on the key on 17 M but the cover is off.
What I am wondering is if I should use the same coupling cap and RFC bypass as 
Ameritron uses in the AL-80B with their choke.  They use 0.002 coupling and 
0.001 bypass. 
I kept what was in the Alpha for RFC bypass and installed a big Russian 0.002 
coupling cap. 
At the bottom of the choke is a 0.006 (three 0.002's) to ground, a 15uh series 
choke and a 0.008 (four .002s) to ground that go to B+.
The original Alpha arrangement was 0.004 coupling, 0.004 bypass, 15uh series, 
0.004 bypass.
I don't know what the best thing to do is.  I wondering if the 15uh is 
necessary or screwing up the Ameritron.
Any comment will be greatly appreiciated.
Rick N6PE

Rick, N6PE
 Talk is cheap... except when Congress does it.
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