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[Amps] SB-220 Output Network

Subject: [Amps] SB-220 Output Network
From: "jim.thom" <>
Date: Thu, 12 Aug 2021 18:31:16 -0700
List-post: <>
Date: Thu, 12 Aug 2021 11:57:07 -0500
From: Joe <>
To: Amps group <>
Subject: [Amps] SB-220 Output Network

<Now how much "L" is needed with the rest still stock?
<for each band?

<and using the stock 1.75" coil form, how many turns should be the best
<chance of working for each band segment?

<Anyone willing to try a gander at this?


###  use the  GM3SEK  PI software.  Its the  gold standard for designing PI
nets.  Then there is  NO guessing, or copying others  mistakes.

##  You dont mention  how much plate current you are drawing, nor how
much idle current.  Nor how much bias V is being used.
Do u want  1.5 kw PO on  RTTY  and  FM ?    Since u increased the  B+..and
assuming the plate current remains the same, your plate load Z just
increased by a bunch, which will require MORE  L..and  LESS  C!  +  C2.  If
you dont do that, your loaded  Q just increased by a bunch..and you will
cook the coils and the poor bandswitch.

You will require a huge increase in cooling  for  1.5 kw  rtty operation.
Ideally, if a hb supply is used, or a replacement inboard  hypersi xfmr,
get one with taps on the pri or sec, so you can run reduced B+.  Then with
a commensurate  reduction in plate current, the plate load Z wont change in
value.   Thats the eff way to run reduced power, if required, efficiently.

##  I use the GM3SEK  PI  software on a continual basis, all year round.
 This is mainly for  hb  multiband amps, and also HB  monoband amps.   I
use K6STIs  coil  4.19  coil software to design the coils. It now also
handles  strap coils.... up to  1 inch wide....and also tubing coils up to
1 inch diameter..and also any wire gauge u want.   Armed with a digital
LCR meter, to measure both caps, etc,  its relatively easy to get
everything dialled in correctly..and max obtainable eff on each band.

##  The software also allows you to adjust the loaded  Q  for each band,
and also factors in stray C,  tube C..and any stray L.   The end results
are always dead on, and predictable.

Jim   VE7RF
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