[ARC5] BC-453 Current Draw

[Ian Wilson]

I think the biggest attraction is that there is no need to replace old and
probably leaky caps if you can keep the B+ down to 60V or so,

73, ian K3IMW


On Tue, Jan 20, 2015 at 10:43 PM, Scott Robinson <spr at earthlink.net> 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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