[sdiy] AN299 VCO (was: SDIY list troubles)

[Ian Fritz]

At 06:16 PM 4/29/2008, Paul Perry wrote:
>Anyone using the CA3046 in feedback stabilized heater mode, note that the
>transistors in the chip have to be the same ones used in the application
>note.
>Although the transistors are identical electrically, because of the
>different physical placement in the chip, for the heater & sensor
>transistors to operate properly, I think they have to be as shown in the
>note.
>
>I haven't tried this circuit myself, but I seem to remember seeing something
>about this.

I've heard that too, but I don't understand it.  Aren't Q1 and Q2 the best 
matched pair, wherever they are located on the die?  I mean, on the wafer 
the matched pairs aren't always in the same relative location.

But the important point is that several list members have reported that the 
circuit works, so people shouldn't be put off from building it because of 
one or two failures.

Ian