[ARC5] BC-453 Current Draw

[Leslie Smith]

  Hi Dennis,
  If you look at the circuit diagram, and if you don't have a rack to
  slide your set into (but just use a 7 pin socket) and you lift the
  bottom of the screen divider from ground, then the screens will run
  with B+ potential.  I do this, using 60V B+.  I'm sure most
  list-readers will know this trick.
 (But sometimes I forget this sort of trick.  :-)   )

  73 de Les Smith
  vk2bcu at operamail.com


On Wed, Jan 21, 2015, at 17:20, Dennis wrote:
> It just occurred to me while looking over the schematic that the voltage
> divider feeding the screens is 14K across B+.  That represents 5 mA at
> 70V, nearly half the draw. If one were to lift the gnd connection of the
> bottom resistor the divider current would go away, leaving just a small
> screen draw.  The radio's low B+ performance would likely improve due to
> the higher screen bias.
> 
> Dennis AE6C
> 
> Sent from my iPhone
> 
> > On Jan 20, 2015, at 8:27 PM, Dennis Monticelli <dennis.monticelli at gmail.com> wrote:
> > 
> > OK guys.  Here is the report on current draw vs B+.
> > 
> > First the working conditions:
> > 1) Western Electric BC-453-B in very good overall condition with the only modifications being 12V heater wiring (not by me) and a complete re-capping (guilty).  No changes were made to the biasing of any circuits.
> > 2) FT-260-A adapter box
> > 3) 12.6VDC filament power from HP bench supply
> > 4) Variable source of B+ from a Heathkit PS (external accurate metering)
> > 5) AF impedance transformer driving an 8 ohm speaker
> > 6) Gain control set to about 3/4 with volume varying from soft to loud depending upon B+
> > 7) RF source was a magnetic loop with preamp (Pixel Loop)
> > 
> > B+      mA       Comments
> > 24      3.5        barely alive  
> > 30      4.5        audio at a whisper
> > 40      6.0
> > 50      7.6
> > 52                   the BFO starts up and stays on until the B+ drops below 30V
> > 60      9.2
> > 70     10.9
> > 80     12.6
> > 90     14.2
> > 100   16.0
> > 110   17.5
> > 130   21.0
> > 150   24.3
> > 170   27.8
> > 190   31.3
> > 210   34.8
> > 230   38.3
> > 250   41.8     audio is pretty loud now but distortion acceptable
> > 
> > Notes:
> > 1)  The BFO has a very minor effect on current draw (small fraction of a mA)
> > 2)  The audio output does boost the current draw when it gets loud but only by a few mA
> > 3)  Your mileage may vary, especially if your caps are original.  Leaky caps at the higher voltages in particular would increase the draw.
> > 
> > Hope this data is helpful to the group.
> > 
> > Dennis AE6C
> > 
> > 
> >> On Tue, Jan 20, 2015 at 7:01 PM, Bill Cromwell <wrcromwell at gmail.com> wrote:
> >> Hi Scott,
> >> 
> >> Some of the ham modifications include installing a separate audio gain but most (that I know of) do not. In the discussion in this thread the OP has already corrected his question to your suggested intension.
> >> 
> >> 73,
> >> 
> >> Bill  KU8H
> >> 
> >> 
> >>> On 01/20/2015 08:57 PM, Scott Robinson wrote:
> >>> I presume you mean RF gain not audio gain, yes?
> >>> 
> >>> /scott
> >> 
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