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[Amps] Plate choke design L?

To: <>
Subject: [Amps] Plate choke design L?
From: "Jim Thomson" <>
Date: Sat, 8 Dec 2018 09:38:14 -0800
List-post: <>
Date: Thu, 6 Dec 2018 22:11:50 -0500
From: "Tim Duffy" <>
To: <>
Subject: [Amps] Plate choke design L?

<For best plate choke performance on 160 meters - what is the inductance that
<results in best 160 meter amplifier performance?
<Using a 8877 tube here.


<Tim K3LR

##  On  a  160m  mono band amp..with a 8877.   300-400  uh  would be optimum. 
Assuming  plate current of no more than 1 Amp,  27 gauge  would easily handle 
the job.
With mono band amps,  you get to optimize the plate 
choke..and not have to
worry about a 1st series resonance on   say  80-40-30m. 

##  But you may well have total length constraints...esp if larger gauge magnet 
wire used, like 24-22-20.  
Is the proposed 160m choke to be mounted vert, or horz ?   On hb plate chokes, 
I use  solid teflon rod,
typ  the one inch type.  Any coil calculator will  spit out the number of 
required turns for a given uh, or 
wire gauge to fit  XXX  number of turns, onto a max length rod.   If you run 
out of length, then increase 
the rod diameter, like to 1.125 or 1.25 inch,  or even bigger. I drill and tap 
the bottom of the teflon rod with
a .25-20 thread, then use a 1 inch long .25-20 nylon  bolt, to bolt it to the 
chassis.... when mounted vert.  
Transverse 8-32 brass screws  at each end of the winding to terminate the 
windings, etc.  

##  A lot of amps will  feed  B+  up through the plate choke, then feed the B+  
through the parasitic suppressor,
then to the anode.   For better stability,   I never feed B+  through the   
suppressor.   Even if no suppressor used,
the B+ goes from top of plate choke..straight across to anode...and not the 
anode connector in the center of the tube,
but the outer ring, at the top of the outer ring, shell.    Then  the RF path  
is from  another portion of the outer ring,
over to the plate block caps.    Those 2  connections are like    90-150 degs 
apart..depending on config. 

##  Funny you mentioned a 160m  plate choke, since Im in the middle of 
designing a mono band  160M   YC-156 amp
for a buddy, but that is a taller tube than a 8877.   Mounting a plate choke on 
a side wall is ok too, as long as each end is 
supported, and spaced away from any side wall.   For  160m use,   2-3   X   
4700 uf  ceramic bypass caps used at
cold end of 160m plate choke.   I use  ceramite brand,  available from mouser 
and also henry radio,  since  I could get 
em in 10kv and also  15 kv ratings.   5 or  7.5 kv would be ample for a 8877, 
depending on un loaded B+ values. 

Jim  VE7RF 

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