[ARC5] BC-453 Current Draw

Wed Jan 21 02:20:36 EST 2015

  Hi Scott,
  There are several advantages.

  (1) If you don't have a dyno, and you do have a 24V AC 1A transformer
  handy, you can power the set from a single transformer.
         (Particularly useful if you don't have a rack either).
  (2)  Running on 60V B+ the tubes run wonderfully cool, and this gives
  a longer life for your tubes, and (for the HF sets) better stability.
  (3)  60,000mV is much safer than 200 or 250 volts.

  73 de Les Smith
  vk2bcu at operamail.com

On Wed, Jan 21, 2015, at 17:43, Scott Robinson wrote:
> Folks,
> 
> I must be missing something. With KW at your friendly neighborhood mains 
> socket, what's  the interest in running a receiver with big heater mains 
> tubes (valves) on such low B+?
> 
> Curiously yours,
> 
> /scott
> 
> On 1/20/15 10:38 PM, Leslie Smith wrote:
> >    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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