The 2N2/256-BSCP [was: Homebrew Drum Computer]

dwight elvey dkelvey at
Fri Dec 21 10:55:06 CST 2007

> From: dkelvey at
> To: cctalk at
> Date: Fri, 21 Dec 2007 08:21:53 -0800
> Subject: RE: The 2N2/256-BSCP [was: Homebrew Drum Computer]
>> From: mcguire at
>> Date: Fri, 21 Dec 2007 08:52:06 -0500
>> To: cctech at
>> CC:
>> Subject: Re: The 2N2/256-BSCP [was: Homebrew Drum Computer]
>> On Dec 21, 2007, at 2:07 AM, dwight elvey wrote:
>>> As a cheaper alternative to a tunnel diode, do a search for
>>> a Lambda Diode. I used one of these circuits once to make an
>>> oscillator that ran at over 100MHz.
>> Oh my, there IS an almost-equivalent-to-a-tunnel-diode circuit!
>> That looks really, really neat...I will have to play with that!
> Hi
> To better approximate a tunnel diode, you'd have
> to put a resistor in parallel. I don't recommend doing
> this as it only degrades the negative resistance.
> Still, if one was to use a pair of these for a flop, it
> might be more stable since at the higher voltages,
> unlike a real TD, it completely shuts off. Without the
> shunt resistors to bypass some current the circuit
> might oscillate.
> Dwight

 Another negative resistance device is the DIAC. These are
really cheap but these are knee type curves instead of
S type, like the TD and Lambda.
 One would have to rearrange these in a parallel configuration
for a latch or flop, similar to the neon circuits.
 The TD has the advantage that the stable state is lower
current, not higher current.
 The disadvantage is that that tends to increate the impedance
of the storage net making it less stable and more susceptible
to noise. That is why I recommend the shunt resistor to
decrease the impedance.

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