[ARC5] Reverse engineeing the BC 456

[John Hutchins]

Chris -

  there was many recent emails, last year, on milsurplus at mailman.qth.net 
on this subject.

Schematic and parts list.

Hutch


On 3/18/2017 2:45 PM, Chris Bowne wrote:
> Many years back someone had a simple circuit published in ER of an 
> electret element mic and I believe a source follower low impedance 
>  output stage with appropriate gain ahead of it to provide more than 
> ample drive for the various WW2 sets that were designed to be used 
> with a T-17 carbon mic, maybe someone can supply the particular issue 
> to look for it in.  If you can't fit all the components in the T-17 
> case, why not just have them in an in-line tube of appropriate size on 
> the mic cable?
>
> Sent from my iPhone
>
> On Mar 18, 2017, at 13:46, J Mcvey via ARC5 <arc5 at mailman.qth.net 
> <mailto:arc5 at mailman.qth.net>> wrote:
>
>> My idea to to modulate the bc456 with a 'level shifted" electret mike 
>> hit a snag.
>>
>> The mike input transformer has ratio of 1:10 primary to secondary 
>> which is terminated with about 3000 ohms which means that the primary 
>> is looking to match a 30 ohm device?
>>
>> That explains why the modulation is so poor. My T-17 likes to be 
>> around 2K.
>> It also precludes using the electret output directly because the 
>> internal fet needs a drain resistor of 2- 5k to provide the gain, 
>> requiring a medium Z to match.
>> Bummer...
>> Nothing is ever simple...
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>
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