[Milsurplus] OK Smart People- Back Bias

[J. Forster]

You misunderstand.

I was suggesting applying the grounded B+ supply between A- and B+

and

applying a negative bias voltage (from AAs, for example) between A- and B-

-John

==============



> You can have the last word by stating the obvious. - Mike
>
> Sent from my iPad
>
> On Jul 31, 2012, at 5:39 PM, "J. Forster" <jfor at quikus.com> wrote:
>
>> http://home.netcom.com/~arc5/bias/backbias.jpg
>>
>> The best way to run the thing is to develop the negative bias voltage in
>> as similar way as it was originally, essentially aqpplying the bias
>> between A- and B-.
>>
>> -John
>>
>> ================
>>
>>
>>
>>> I do not see that circuit. In the circuit shown, there is no way it
>>> would
>>> work. Of course a battery would, but, my comment that you had to find
>>> fault with, was on his Zener circuit shown. - Mike
>>>
>>> Sent from my iPad
>>>
>>> On Jul 31, 2012, at 5:10 PM, "J. Forster" <jfor at quikus.com> wrote:
>>>
>>>> Originally, Dave's circuit shows the negtive bias is developed across
>>>> the
>>>> 620 Ohm resistor in the B- line.
>>>>
>>>> That voltage is essentully filtered and applied acrossa the 20k pot.
>>>>
>>>> If a 9V battery replaced the voltage developed across the 620 Ohm, the
>>>> circuit would be battery, Zener, 20k pot.
>>>>
>>>> -John
>>>>
>>>> ===============
>>>>
>>>>
>>>>
>>>>> Well John, even if that were true, where are those micro amps coming
>>>>> from
>>>>> in that circuit? - Mike
>>>>>
>>>>> Sent from my iPad
>>>>>
>>>>> On Jul 31, 2012, at 4:48 PM, "J. Forster" <jfor at quikus.com> wrote:
>>>>>
>>>>>> Depends on the Zener. Some have very sharp knees in the microamp
>>>>>> region.
>>>>>>
>>>>>> -John
>>>>>>
>>>>>> ================
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Dave -
>>>>>>>
>>>>>>> The Zener idea will not work due to the real high resistance values
>>>>>>> in
>>>>>>> the
>>>>>>> existing circuit of the 474. 73 - Mike
>>>>>>>
>>>>>>> Sent from my iPad
>>>>>>>
>>>>>>> On Jul 31, 2012, at 11:51 AM, "David Stinson" <arc5 at ix.netcom.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> I have a BC-474 receiver that, as originally designed,
>>>>>>>> uses a backbias resistor in the B- lead to provide audio
>>>>>>>> PA and AVC bias.  R25 and C21 provide the bias.
>>>>>>>> Here's the diagram:
>>>>>>>>
>>>>>>>> http://home.netcom.com/~arc5/bias/backbias.jpg
>>>>>>>>
>>>>>>>> I'd like to make a temporary "tacked-in" change so I can
>>>>>>>> use a supply with B- grounded for a short time.
>>>>>>>> Will 5-volt zeners connected this way work?
>>>>>>>>
>>>>>>>> http://home.netcom.com/~arc5/bias/zenerbias.jpg
>>>>>>>>
>>>>>>>> Thanks!
>>>>>>>>
>>>>>>>>
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