[Amps] Alpha 77 160 meter plate choke

[Paul Christensen]

Tree,

You may want to check for any in-band resonances if you haven't already.  In 
my 77Dx, I've also added additional C  from +HV to ground.  For the upcoming 
77D project, the plan is to discard the B&W 801 choke and replace it with an 
RF Parts RFC-3.   This choke should provide ample 160m inductance and is 
stagger-wound to minimize or eliminate in-band resonance but needs to be 
validated after installation.  Specs are:  1.5A, 225 uH, 4 KV max.

Paul, W9AC


---- Original Message ----- 
From: "Tree" <tree at kkn.net>
To: <amps at contesting.com>
Sent: Monday, March 24, 2014 2:17 PM
Subject: [Amps] Alpha 77 160 meter plate choke


> All -
>
> I have made a mod to my Alpha 77 to add about 60 uH to the RF plate choke
> when on 160 meters.  I originally was going to mount a switch to control a
> HV relay - but came up with a better solution.  If you are interested in
> knowing more - check out the pictures here:
>
> http://www.kkn.net/n6tr/directories.html
>
> Look under Alpha 77Dx.  The relay was purchased from Henry Radio.  It has 
> a
> 26.5 volt coil which seems to work just fine off of the +24 volt regulated
> power in the amp.
>
> I added a 4700 pf 6KV cap from the HV to ground which you can see in the
> pictures.
>
> I am not sure this makes a big difference - but I certainly feel better
> about using the amp on 160 with this mod.
>
> 73 Tree N6TR
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