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Low voltage tube crystal oscillator ALC

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neazoi

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Hi, I have built and tested this oscillator http://qrp.gr/tubeosc/

The variable capacitor setting, greatly defines the output distortion. For low distortion, the capacitor needs to be set for minimum signal output that allows for reliable start up of the oscillator.

This is a pierce circuit, so many crystals should work with it. But I want to make this capacitor setting automatic, so that low distortion is achieved automatically for every crystal inserted into it.

How can I achieve an ALC for the oscillator? Different ways, ideas, are all appreciated. I prefer doing it solid state-free but if there is no easy way, solid state devices are also accepted. Note, I am using only one of the two tube triodes, so the other one can be used for the purpose. Anything from LDRs, varicaps or other means are accepted, all ideas will be valuable.
 

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    neazoi

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Ah, I remember this bulb method used on audio oscillators. I have also fount this http://www.valvewizard.co.uk/localfeedback.html a resistor from the output to the grid input should provide negative feedback, but could this perform the function of ALC really?
Maybe the bulb in series with that resistor can do the trick. But I do not think there sill be enoigh signal to heat up the lamp in this oscillator. MAybe some kind of pre-bias for the lamp can be used.
 
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