[sdiy] 3046 vco help?

[Dave Kendall]

Hi all.

On Aug 18, 2011, at 20:08, Magnus Danielson wrote:
> The lower left transistor pair is the expo-pair. The collector on pin 
> 1 pulls current through from the 10 nF capacitor which is then being 
> buffered by the J112 FET which essentially acts like a emitter 
> follower.
> The output of that is being tossed into the upper pair which acts like 
> a comparator which with the 2N3906 acts like a reset of the 
> sawtooth.Finally, the 2N3904 is the output comparator for the square 
> signal.
>
> There it is. Not too odd setup. The "benefit" of this is the lack of 
> high gain in the feedback path, which can make it warmer due to the 
> inherent trigger jitter, but explaining that can be a bit tricky, but 
> I could go into that if you need me to. Fun thing. Does it sound good?
>
> Cheers,
> Magnus

Hi Magnus - going into the detail would be great - thanks -  but like 
Dan I'm really interested - it seems like such a simple low-parts count 
dual OSC - 3046's are still available in SOIC last time I looked, and 
you can still get NOS ones if you look around..

On Aug 18, 2011, at 22:25, KA4HJH wrote:

> As I hazily recall the heater took longer to stabilize and a tempco 
> was much simpler. Tom had them in stock, too, so the choice was easy 
> I'm sure I have the entire conversation about it in my email 
> archive--somewhere.

  Terry - I'd be very interested in seeing that conversation if you 
could dig it out without too much trouble for yourself.... I've got 
some 1K tempcos (only 3000ppm though) lying around, and a few VCO3D 
boards...
>
>> Tempcos might be hard to get and cost more...Heater uses much more 
>> power, excess heat might make other components drift...(I use tempcos 
>> epoxied to dual transistors, usually...)
>> H^) harry

A plan might be to use Ian Fritz's transistor matching circuit to get 2 
matched trannies and build up a dual tranny/tempco thermally connected 
epoxy "lump" then... seems like that would help stability....

Thanks all for the responses.....

cheers,
Dave