[sdiy] Modern transistor matching

[Grant Richter]

>
> The Dual 3904s seem to be quite well matched and the low mass of  
> both the transistors and 0805 T. resistor
> means they will probably remain very close to the boards temperature.
>

The last bag of 100 x 2N3904 transistors I got from Mouser, I sorted  
them by my usual method.

All 100 tested +/- 1 mv. of each other at room temperature (all 100  
came out of bag matched to each other to Moog spec.)

Either I lucked out and got a chance pull from a single process bin,  
or process control is getting good enough to control semiconductor  
doping down to the molecular level.

I couldn't believe it so I checked some with different equipment,  
same result.

I have also noticed that a bag of 200 x 5% resistors also seem to  
match to 1% or better within the same bag (to each other but not to  
spec'ed value).

I used to have to do all that X-bar chart process control stuff, it  
seems like SOME processes are quite under control today.