That 15uH is there as a VHF choke and is completely useless. Replace it with
a glitch resistor.
Insulating the new choke with Teflon or Mylar sheet at the arc points is
worth a try.
Carl
KM1H
----- Original Message -----
From: "rick darwicki" <n6pe@yahoo.com>
To: <amps@contesting.com>
Sent: Tuesday, April 10, 2012 8:48 PM
Subject: [Amps] Plate choke help.
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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