Transistor Substitution

[Allison]

Ethan Dicks wrote:
> On Tue, Jun 9, 2009 at 5:38 PM, Allison<ajp166 at bellatlantic.net> wrote:
>   
>> Way too much information..  What he needs to know is what can he buy now that
>> should work to replace a 2n3009?
>>     
>
> I could use that info, too, since I also have older DEC equipment that
> uses the 2N3009.
>
>   
>> Answer: the 2N2222A (metal can not the plastic PN2222) has the same or close
>> enough FT, Ic and breakdown voltages.  It would be my first choice if I could
>> not purchase/salvage the exact part. Also the 2n2222A is available and usually
>> cheap.  I buy them usually in for groups of 25 for about $0.08US each.
>>     
>
> What is different about the metal can and the plastic case part?  I
> have a few of each, and have so-far interchanged them in circuits
> where performance isn't an issue (i.e., where a 2N3904 would work
> fine, too).  Obviously 2N2222s aren't expensive, but I'd like to know
> why I should set aside the metal-cased ones for repairing specific
> items.
>
>   
They are essentially the same die but due to mounting and the absence of 
the metal the
pn2222 does not stand he same Ic and power dissapation.  if you really 
need the plastic
part you might as well use the 2n3904.


>> The only case where they type transistor is a bit fussy is some of the faster
>> flip chip cards (logic) and SMPS.
>>     
>
> What categories of FLIP-CHIPs are you thinking of when you say
> "faster"?  I have three R-series CPUs and a few DF-32s.  I have yet to
> delve into component-level repair, but I know I'll need to soon.
>
>   
some of the older boards that used transistors for logic.  one place  
you would see those is
in an 8l or straight 8 and part of the core memory subsystem of the 
omnibus machines.

>> FYI: Older DEC machines like straight-8 and friends used a lot fo the ceramic
>> epoxy parts similar to the 2n3638 and 2n3563.
>>     
>
> Good to know (since I have more than one item from that era).
>
>   
>> Those are ceramic headers with
>> a block of epoxy covering the die and are prone to popping the epoxy and the
>> symptom works when cold or mechanically intermittent.
>>     
>
> Is that visually apparent, or is that an internal fault?  If I
> identified a bad transistor and removed it from a FLIP-CHIP, would it
> be difficult to set up something with an oscilloscope to watch some
> output then tap on the transistor to watch the trace "change" to
> verify mechanical fragility?
>
>   
Its rare to see the top epoxy pop off but it happens.  usually the part 
either fails
or  is most often thermally intermittent.

Lot's of years working with transistors from that era and noo small 
amount of DEC scrap
boards during my time with DEC for spares and as resource.

Allison
 
> Thanks,
>
> -ethan
>
>