[Amps] Output choke - Calculation

[Jim Thomson]

Date: Thu, 17 May 2012 15:09:33 +0000
From: M?ximo EA1DDO_HK1H <ea1ddo at hotmail.com>
Subject: Re: [Amps] Output choke - Calculation
To: <amps at contesting.com>
Message-ID: <DUB110-W50F0ABF719B8312CD6CE7295190 at phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"


Hi all,

Now I have more clear the idea.

Thank you to all of you

73, Maximo




> From: km1h at jeremy.mv.com
> To: k8ri at rogerhalstead.com; amps at contesting.com
> Date: Thu, 17 May 2012 08:18:32 -0400
> Subject: Re: [Amps] Output choke - Calculation
> 
> The ones used on most amps is 1 to 1.5mH, 100-300ma
> 
> Carl
> KM1H
> 

### maximo,  your typ 1 to 2.5mh  100-300ma choke will blow up in your face every time, if just one
plate block cap fails.  I have a lot of experience with this.  Those small pi wound chokes have wat too high a dc resistance,
typ as high as 40 ohms.    A better choke for the job is a small 45 uh choke, solenoid wound. 18-22 ga  magnet wire,
wound on a .75 inch to 1.00 inch  form, like solid delrin or teflon rod, or ceramic rod. 
Another choke that will also work is a 45 uh choke, but wound with 12-18 ga
magnet wire, and wound on a 2.4 inch OD torroid, like type 43 or type 33 material. 

##  45 uh is plenty for the job, and will easily work on 160-10m.    Just wire it between the hot side of the
load cap, and the chassis, if a simple PI net is used.  If a PI-L is used, wire it between output end of the L coil
and chassis. 

##  I usually wind a 2nd identical 45 uh choke... and wire the 2nd choke between hot side of EITHER the
input or output coax connector.... and chassis.   The purpose of the 2nd 45 uh choke is so the hot side of the
coax is DC grnded to chassis  on RX.  Then the 2nd choke will bleed off any static charges, etc,  built up on the
ant during RX.  At the VE7ZZZ MM contest site years ago, the 160M dipole  would pick up so much 
static buildup, that the S-meter  would slowly rise to way over S-9. When the ptt or vox was tripped for just
a second, the RX nosie would drop way down.  Then it would slowly build up again. 

##  The 1st choke across the load cap will  drain the static build up.... but ONLY on TX !    The 2nd choke
will drain the static on RX.  

##  wire a  1-3.5 mh  @  100-300 ma choke via a vac relay..across your B+  supply... then activate the vac relay.
The choke will  explode  every time.   12-22 ga magnet wire won’t do that.  45uh is plenty, since it’s located at a 
50 ohm point.   Every commercial 5-15 kw amp I have seen uses the same 45uh safety choke set up.

Later... Jim   VE7RF