[ARC5] BC-453 Current Draw

[Dennis]

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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