[Amps] Grid Bias Supply followup

[Steve Flood]

I think I see now - I had to redraw it to understand.  During receive when the T/R switch/relay is open, the -100vdc appears on the grids in reference to the filament(cathode) which is at DC ground via the filament transformer center-tap.  Is that correct?   And during transmit, the T/R switch/relay closes and the rheostat is a divider that provides the operating bias voltage to the grids.

  ----- Original Message ----- 
  From: TexasRF at aol.com 
  To: kk7uv at bresnan.net ; amps at contesting.com 
  Sent: Saturday, March 22, 2008 7:53 AM
  Subject: Re: [Amps] Grid Bias Supply followup


  Perhaps the -100vdc is used for cutoff bias in receive?

  A typical t/r circuit might use a set of relay contacts to lift the + end of the rheostat from ground on receive thus allowing the full -100vdc to appear on the center of the rheostat and tube grid(s).

  73,
  Gerald K5GW



  In a message dated 3/22/2008 6:26:27 A.M. Central Daylight Time, kk7uv at bresnan.net writes:
    As a followup to my question about the grid bias supply on the G.E. Ham News 813 amp (and the B&W LPA-1 is nearly the same design):  

    The bias supplies for these amps use a 120:120 transformer, half-wave diode rectifier, C/RC filter (40uF/500 ohms/40uF) and a 500-ohm, 25-w rheostat load for the adjustable bias.  These supplies are said to provide zereo to -100v bias.  Yet, the settings for CW and SSB only use -19 volts and -5 volts.  Why then, is it necessary to have -100 volts available?  Seems like a much smaller supply would suffice.

    Thanks, Steve KK7UV
    _______________________________________________
    Amps mailing list
    Amps at contesting.com
    http://lists.contesting.com/mailman/listinfo/amps







------------------------------------------------------------------------------
  Create a Home Theater Like the Pros. Watch the video on AOL Home.