[sdiy] CA3086 and CA3046?

[Christian]

On Thu, 16 Aug 2001 12:20:11 +0200, Rene wrote:

>>I'm making a VCO using the CA3086 at the moment.
>>Should I use the two transistors to the left of the chip which already
>>share a common emitter?

>Yes, that way you can put in a 3046 later and have the transistors matched.

Mmmmmmm - I can't get a 3046 from anywhere - That's why I got the
3086's instead. I admit that I thought they had transistors that were
matching, but looking at the online datasheets indeed they are not.

I managed to get quite a few (10) 3086's and I shall test the
transistors to attempt to get the best match. When all said and done,
if the VCO works and is stable then it doesn't matter what you use.
If she drifts like a ship lost at sea then I shall think again.

Another question. Anyone doing anything fancy with Pin 13 (substrate)?
I am currently tying all spare transistor bases and emitters to ground
(which includes that pin).

>>Also, Farnell Electonics supplier here in the UK has discontinued the
>>range of 1K Tempco resistors but they will supply a 1K Thermistor
>>(code 679331) in its place which I am going to try to use. Anyone any
>>thoughts or things to add?

>I don't know that part, but thermistor sounds like negative temperature
>coefficient. If so then you will need to put it in the upper leg of the
>voltage divider. (An example of how to do that is on my homepage -> click
>"whats that exp and tempco stuff".)

I concur - Thanks Rene.

Incidentally, the Tempco resistor I was asking Farnell for was code
679331. This has been discontinued, but an identicle resistor (1K
3000ppm/degree C) is available as code 732278 (Thanks Tony).
I'll shelve my NTC thermistors for another day.

Thanks
Christian.