[Amps] Tips For Winding a Plate Choke

[Jeff Blaine]

This is a project that can be a great lesson learning opportunity.  
After all, how hard can it be?   Ha ha.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 10/10/19 4:08 PM, Jim Thomson wrote:
> Date: Thu, 10 Oct 2019 11:38:25 -0400
> From: Roger D Johnson <n1rj at roadrunner.com>
> To: amps at contesting.com
> Subject: Re: [Amps] Tips For Winding a Plate Choke
>
>
> <A simpler alternative is to switch another choke in series for the lower
> <frequencies. This is quite simple to do. Think of two chokes in series
> <with a capacitor connected to the junction of the chokes. A relay grounds
> <the other side of the cap on the high frequencies thereby effectively
> <removing the lower choke from the circuit.
>
> <73, Roger
>
> ##  That trick  was  used  by  asi,,and  its  forerunner  company.
> 50uh  +  135uh.  Both chokes  used  on  160m.    50uh  choke  used
> on   80-10m.
>
> ##  Both  chokes  in  series cant  be  used on  80m......  u  will  get
> fireworks  and  huge  arcs  across the  junction point....and  also
> fried  relay  contacts.
>
> ##  Buddy  tried   135uh  +  50  uh...and  also  170uh  +  50  uh.
> Same  deal,  both  in  series  can  only  be  used on 160m  only.
> Since  the  HB amp   was  160-15,   final config  was  135uh  +  70 uh.
>
> ##  One  other  important  note,  3 x  1 megohm  3 watt  mofs  in  series
> are  wired  between  relay  contact  and  chassis. ...  IE:  cold  end  of cap.  THEN  the  junction cap
> is  in  DC  block  mode.    With the  spst-NO  mech relay  energized,  the
> Cap  is  now  RF  grounded...as  well  as  DC  grounded     Without  the  3 x megs   in  place,  u  will get
> arcs  across  the  open contacts when  relay  de-energized.   Reason is  cuz
> of  the  leakage R across the  cap....  even  HEC   HT-57   15  kv  types.
>
> ##  we  tore  our  hair  out trying to  figure it  out.    In  desperation,  we  noticed
> Alpha used  the  same  2 x choke  config  +  junction cap......  but  used spare contacts on  bandswitch
> instead  of a relay.  Alpha  used  3 x 1 meg,  1/2  watt  Carbon  comp  resistors  in  series.....wired in parallel  with
> contacts.   Cold  side of cap  is  dc  grounded on  low  band....and  RF +  dc  grounded  on  high  bands.   So  we ripped
> off  the alpha resistor concept.....  which  works.
>
> ##  another  method Is  2 x chokes, big and  small....  with  bottom of each choke fed  with  B+.  Bypass  caps
> at base of  each  choke.   A  spst  vac relay  with  COM  wired to anode.   NC wired to  top  of  1st choke.
> NO  wired to  top  of  2nd  choke.   Be  careful with this config !    Vac relay will  have  B+    plus  peak  RF  voltage
> on  its  contacts.   When  tube  is driven  full  bore, the  RF  voltage  developed in the  tank  circuit is AC.....and  will
> backfeed  through the  plate  block  caps.....and  superimpose  itself onto  the anode.   Total peak  V  will  be a little
> bit  less  than double the  loaded  B+  voltage.   The  advantage is.... each  choke  can  be  optimized.   IE:  200-300  uh
> for   160+80m  for  choke one......... and   50uh  for  choke  two.   The  drawback  is... the  spst vac relay  has to be  able to
> withstand the  B+   and the  rf  peak voltage.   RF  voltage rating of vac relays  drops  like a rock  as  freq  increases.
>
> ##  The  ameritron  choke....if  u  cant make  it  fit....  is the cheap and easy way  out....even if a few turns  have to  be
> removed  from the bottom...as  in  martins 30m  band issue.
>
> ##  2 x ameritron  chokes... WELL  spaced  apart..with separate  B+  and  bypass  caps  at  base of each  choke....  and  each  top separately
> wired  to anode....  will  also  work.  aluminum  bar  acrosss  the  tops  of a pair  of 15 kv  HEC  bypass  caps.  Choke  mounted on  top  side
> of  al  bar...dead  center.   Used  for  amps  that  require   up  to  3A   of plate  current.   Then  u can  use 8  kv  for  B+.
>
> Jim   VE7RF
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