[Amps] AL-1200 pi input network. is manual right for correct "stock" LC values?

[knormoyle at surfnetusa.com]

I just got done redoing the input network on my old FL2100b (adjust 15m/10m coils and caps) and was 
happy with the result..so I went back to the AL-1200 I've mentioned here before to fix it's issues.


1) Opening up the front panel and exposing the AL-1200 input coils, yes indeed, the ferrite had 
fallen out of the 10m coil. The 15m ferrite had been turned in too far for my hex tool to reach it.

2) 10M couldn't be adjusted. I noticed it had just 1 turn for the "coil" ...so I disconnected the 
coil and replaced it with a wire (basically just across the bandswitch). 10M looks good now. (it had 
been centered lowerbefore I lowered the L by removing the one turn coil)
I wonder if they had tuned 10M when they manufactured it..since it shipped with the green wire 
disabling 10m.

3) I was surprised at the poor way the wires had been arranged. The leads from the input coils to the 
bandswitch seemed excessively long and the wires weren't arranged to minimize coupling. Also the wire 
insulation seemed cheap pvc? (not teflon). I rearranged things, just because I had seen how dressing 
had affected 10M/15M on the fl2100b.

4) Surprisingly, the input network is a Pi network (C's shunting both sides of the L) on 160/80/40, 
BUT just an LC network on 20/15/10. I know an LC is perfectly fine but was expecting Pi on all bands.

I looked hard at this, wondering if maybe someone forgot to install some micas, but it appears to be 
the design. 

I looked at the al-1200 user manual, which lists the input network values, and it does seem to show 
Pi network for all bands. It shows 3-1/2 turns for 10M

from the user manual

160M 1300pf, 28t,     2000pf
80M  1300pf, 18-1/2t, 1500pf
40M   500pf, 11-1/2t,  470pf
20M   220pf,  6-1/2t,  180pf
15M   150pf,  3-1/2t,  120pf
10M   150pf,  3-1/2t,  180pf and 27pf? (not sure why they list two here would think it should be 
100pf or so)

So this is odd. My input swr looks good now, except maybe on 40M it could be a little better (1.6:1).
So I'm kind of thinking what I have is what Ameritron ships, but it's different than the above in the 
manual/schematic.
But maybe the above is what it's supposed to be?

Has anyone looked at an AL-1200 input network in their amp recently? Have you seen 10/15/20 as an LC 
network, or different values for L and C compared to what the schematic lists above?

I just got done fixing my fl2100b 10m and 15m input network and had to remove/add 1 turn and adjust 
one side of the Cs. So I'm curious about all this input pi network stuff.

-kevin
ad6z