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
bands.
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.
Thanks,
Rick N6PE
Rick, N6PE
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