[Amps] Re: FW: diode strings...bias

[2]

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>>  -----Original Message-----
>> From: 	Jim Thomson  
>> Sent:	Wednesday, July 31, 2002 04:19
>> To:	'stevek@jmr.com'
>> Cc:	'w6frmarv@dslextreme.com   w8JI@contesting.com'
>> Subject:	diode  strings...bias
>> 
>> steve/rich/marv/Tom
>> 
>> I  got  the  same  results  as  Rich  did,  varying  the  current from
>> 100ma   to  1.2A     Also  tried   40ma  to  800ma,   and  also   350ma
>> to  3A.  regulation  was  in  the  order  of  abt  14%.    Got  the  same
>> results  whether  using  1N5408's   or  using  6A10's.   The  6A10's  are
>> rated  at  1kv-6A-400A  surge,  and  are  double  the  diam  of  a  5408.
>> Same  length  and  wire  leads.
>> 
>> I  also  tried  sticking  a 1000 uf - 50v  rubycom  electrolytic  across
>> the  entire  string.  The  DYNAMIC   reg  was  then  WAY  less  than  14%
>> on  ssb/cw.
>> 
>> 6A  @ .8V =  4.8 Watts.    Hot  as  hell  if  CCS.
>> 
>> I  use  10  x  1N5408's  with  a  1000  uf   50V  lytic  in  all  my  3  x
>> L4B's.    The  drake  L4B  ran  zero  bias  (240ma  idle on ssb
>> position-2600V)   This  mod  dropped  the  idle  down  to 100Ma  on  ssb,
>> and  40Ma  on  CW(1900V)    I  used  a  3  position  center  off  toggle,
>> spdt-center  off  to  give  me  3  positions  of  bias.
>> 
>> Funny,  with  40ma  of  idle  on  1900v  cw  position,  zero  imd
>> results,  as  measured  1/2  mile  away  on  ssb.   Drive  requirements
>> went  up   by  6-8  watts.
>> 
>> Also  tried  grounding  with  some  strap,  just  ONE  grid  pin  of  each
>> 3-500Z.    Drive  requirements  dropped  on  all  bands  by  20  watts.
>> Drake  had  used  3  x 200pf  caps  +  1  choke  on  each  tube  socket.
>> Heath  later  copied  same  ckt.     I  mentioned  this  to  my  buddies
>> with  TL-922's  +  SB-220/  SB-221's.
>> 
>> They  also  tried  the  grounding  just  one   grid  pin  of  each socket
>> and  all  reported   the  same  20w  reducrion  in  drive  power.   

**  Frequency didn't matter?


>> The fellows  with  the  SB-221's  also  reported  that  their  output  power
>> on  10M  shot  up  from 700-800  watts  to 1350-1400 !!  
>>
**   10m is the band where 600pF of grid bypass [XC=9.4-ohms] is 
seemingly enough.  Since a typical "Zero-inductance" 3-500Z 
grid-grounding strap has c. 15nH of XL at 10m, a 600pF  grid-bypass will 
put the grid closer to ground than a strap.

>> The  fellows  with  the  TL-922's  reported  that  they  could  now
>> remove  the  AG6K  nichrome  suppressors,  and  the  TL-922's   were   now
>> rock  stable.
>> 
**  922 / rock stable . . .  I own one and that's laughable.  They are 
[factory-fresh] squirrelier than a SB-220 or an AL-1200 with 
"neutralization".

>> On  the  big  metal  triodes,  I  use  a  12  position  rotary  switch
>> and 50  x 6A10's  +  1  lytic  across  the  entire  mess.  I  tap  right
>> after  diode  #10,  then  every  3rd  diode  after  that.
>> 
>> ...

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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