[Amps] Plate choke design L?

[Jim Thomson]

Date: Thu, 6 Dec 2018 22:11:50 -0500
From: "Tim Duffy" <k3lr at k3lr.com>
To: <amps at contesting.com>
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.

<73

<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 everything.....like 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