[ARC5] BC-453 Current Draw

[Scott Robinson]

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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