[sdiy] uA726, heated pairs...

[Peter Grenader]

OK, I had this idea for the 3046 before I even knew others had done it and a
while back I sat down with the design engineer I trusted the most at M&K,
with a datasheet for both the 3046 and 726 to determine the best way to
duplicate the 726's heater in the other chip - which trannies to keep within
the 3046, which were OK to run externally, etc.

I never ended up trying it, as I soon thereafter learned it was a somewhat
common practice.  I asked Patchell if he felt it was possible at the South
West DIY meet and he mentioned it had been done many times. So I figured if
I ever needed it, I would just poke around and see how they did it.

But I do have those notes if anyone is interested.



 Tim Ressel wrote:

> Grant,
> 
> The substrate needs to be connected to the lowest
> voltage the IC will see. In my case I didn't see that
> part of the datasheet until after I had wired the
> circuit. So I made that transistor unused and replaced
> it with an external 2N4401. Pin 13 (substrate) is tied
> to -V. The 2N4401 replaces the transistor that serves
> as a clamp for the output transistor. I used the same
> scheme when I used a MAT04 which has only 4
> transistors.
> 
> --tr
> 
> 
> --- Grant Richter <grichter at asapnet.net> wrote:
>> Do you remember what you did with the substrate pin?
>> 
>> open, ground or -15V?
>> 
>>> From: Tim Ressel <madhun2001 at yahoo.com>
>>> Date: Fri, 8 Aug 2003 09:23:59 -0700 (PDT)
>>> To: Grant Richter <grichter at asapnet.net>, Keith
>> Daniel <ensign7 at e-scape.net>,
>>> synth-diy at dropmix.xs4all.nl
>>> Subject: Re: [sdiy] uA726, heated pairs...
>>> 
>>> Yo,
>>> 
>>> I use the heater circuit from AN299 on my VCOs.
>> One
>>> uses a 3046, the other uses a MAT04. It works as
>>> advertised. I checked the circuit in an
>> environmental
>>> chamber so I could verify operation up to +40C.
>>> 
>>> --tr
>>> 
>>> 
>>> --- Grant Richter <grichter at asapnet.net> wrote:
>>>>> There is the little known National Semiconductor
>>>> app note AN-299 (1986?),
>>>>> where an LM3046 transistor array is used to
>>>> provide a heated pair for a VCO.
>>>>> 
>>>>> I've tried it, but it seems to me that there was
>> a
>>>> change in chip manufacture,
>>>>> and it doesn't work as advertised. The substrate
>>>> pin is the problem.
>>>>> 
>>>> 
>>>> Just a couple stray thoughts...
>>>> 
>>>> The ap note doesn't specify the pin out on the
>>>> CA3046. You could probably
>>>> get it to work by trying different combinations
>> of
>>>> heater and sensor
>>>> transistor.
>>>> 
>>>> Also, the substrate connects to the most negative
>>>> voltage used, in this
>>>> case, it looks like ground and not -15V.
>>>> 
>>>> For a working example, see the Moog "Source"
>> service
>>>> manual which used a
>>>> thermostated CA3046 for the expo-converter. The
>>>> Serge NTO and PCO also use a
>>>> heated CA3046.
>>>> 
>>> 
>>> 
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> 
> 
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