[Amps] SB-220 bias question

[Carl]

Thats one way of putting it Lou.

Carl
KM1H


  ----- Original Message ----- 
  From: gudguyham at aol.com 
  To: km1h at jeremy.mv.com ; amps at contesting.com 
  Sent: Saturday, August 29, 2009 10:35 AM
  Subject: Re: [Amps] SB-220 bias question


  So in other words it's not a technical issue so much as it is a "idiot proof" fail safe measure?

    Many operate the SB-220 on RTTY and digi modes where the CW position is a key to transformer survivability. 
     
    The same for 12/17M where the tank circuits are far from optimum and bandswitch arcing can occur at 1200W. 
     
    Some owners are a bit slow in tuning up and the CW position reduces the plates from brilliant orange to a darker version. 
     
    Carl 
    KM1H 




  -----Original Message-----
  From: Carl <km1h at jeremy.mv.com>
  To: Gudguyham at aol.com; amps at contesting.com
  Sent: Sat, Aug 29, 2009 9:00 am
  Subject: Re: [Amps] SB-220 bias question


  Many operate the SB-220 on RTTY and digi modes where the CW position is a key to transformer survivability. 
   
  The same for 12/17M where the tank circuits are far from optimum and bandswitch arcing can occur at 1200W. 
   
  Some owners are a bit slow in tuning up and the CW position reduces the plates from brilliant orange to a darker version. 
   
  Carl 
  KM1H 
   
   
  ----- Original Message ----- From: <Gudguyham at aol.com> 
  To: <amps at contesting.com> 
  Sent: Saturday, August 29, 2009 7:09 AM 
  Subject: [Amps] SB-220 bias question 
   
  > It was always my understanding with the SB-220 and other older amps that 
  > the reason for lowering the plate voltage on the 3-500's or whatever tube, 
  > was to comply with FCC regulations. Years ago the rule was 1KW DC input > CW 
  > and 2KW PEP input SSB hence the change in plate voltage. Now that this > rule 
  > has changed I was thinking. It is my observation that the 3-500 tube 
  > performs much better with 3000 or more plate voltage, tube makes nice > power 
  > with lower grid current for the same power at a lower plate voltage. > Hence, 
  > my idea. 
  > I routinely use 7 1N5408 reversed diodes to replace blown zeners. 
  > Expanding on that idea I was thinking of removing the power transformer > primary 
  > windings from the CW/SSB switch and wire nutting the wires together that 
  > produce the higher plate voltage, then making up a small perf board with 
  > about (have to experiment) 11 diodes and using the CW/SSB switch to short > out 4 
  > of the diodes on CW to lower the idle current and have normal SSB idle 
  > current when switched to SSB. That has been the modern day approach to > this 
  > on the newer amps since the FCC ruling has changed. Many hams I know > went 
  > to running CW with an SB-220 and other older amps in the SSB mode anyway. 
  > Thoughts? 73 lou 
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