[Milsurplus] Re: Germanium diodes

[D C *Mac* Macdonald]

As I recall, the bypass capacitor on the emitter resistor
is there to REDUCE the negative feedback that is the
result of increasing emitter current.

Mac - K2GKK/5
Oklahoma City




> Date: Wed, 23 Jan 2008 13:10:24 -0500
> From: jfor at quik.com
> To: brooke at pacific.net
> Subject: Re: [Milsurplus] Re: Germanium diodes
> CC: milsurplus at mailman.qth.net
>
> Take a look here:
>
> http://en.wikipedia.org/wiki/Diode
>
> As to failure modes in early diodes, there could be bond deterioration which would
> primarily alter the forward conduction properties, or die contamination which could
> impact the reverse characteristics. You really need to do a V-I plot to check them
> or try a substitution.
>
> A V-I plot is almost trivial to do if you have even the most minimal X-Y scope and
> a couple of resistors and some kind of an AC source, like a small filament
> transformer.
>
> Best,
> -John
>
>
>
>
>
> Brooke Clarke wrote:
>
>> Hi:
>>
>> I question if the Germanium material was a problem on hot summer days or if it
>> was the circuit design. I seem to remember a college class where we designed
>> amplifier stages using Germanium, Silicon and tubes. In order to maintain the
>> operation point (Ic & Vc) over temperature required strong feedback on the
>> Germanium. With no feedback the Germanium would saturate or open (forget
>> which), but with proper design worked fine.
>>
>> For a common emitter amp the feed back is a resistor in series with the emitter
>> and bypassed by a cap. That stablizes the Ic, Vc over temperature.
>>
>> --
>> Have Fun,
>>
>> Brooke Clarke
>
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