[sdiy] uA726, heated pairs......

[Keith Daniel]

Thanks for the notes! I'm feeling encouraged enough to go back and try it again. 

I had tried the substrate at -15V, open, ground, and even put a low value resistor to -15, and found a voltage drop across it that wandered around with the drifting of the oscillator it was driving. Could be the 20V collector/substrate thing.

I notice that the Moog Source uses an external transistor to drive the heater. Off to the breadboard.

Thanks again, best wishes, all.            kwd...



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>> Do you remember what you did with the substrate pin?
>> 
>> open, ground or -15V?

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>>>> For a working example, see the Moog "Source" service
>>>> manual which used a thermostated CA3046 for the expo-converter.

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>In my own experience with 3046s, which I've used to drive a vactrol LED, I
>found that leaving the substrate floating (not connected to the lowest
>voltage) kept the vac from bleeding when then light was off...

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> Pin 13 (substrate) is tied to -V.

Be careful with this. The collector to substrate breakdown voltage is
only 20V for a CA3046. This is the worst case value, but its best not to
go too near.

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