Expo convertors with tubes ?

[Rene Schmitz]

At 16:08 05.12.99 -0500, you wrote:
>>Here's a quote from one of Eric Barbour's mails on Synth-DIY from July
>>1997 (took me a while to find it):
>>
>>>>You have built an expo converter without linearity problems
>>>>with tubes ?!?
>>
>>>No, I didn't. As someone else pointed out, it is not possible
>>>with tubes. (Actually it is possible but very difficult--it
>>>requires a special tube made by Raytheon in the 1950s, a
>>>square-law tube called a QK329. Very rare today.)

I don't see how this tube could be used to build an expo convertor. 
The QK329 has a square law. 

However I could imagine that an exp (or log) law tube could be made using
the same deflection principle. Replaceing that parabolic shape with an
exponential one.

>Thanx!! That answers one question.  It wouldn't be worth designing an
>exponential converter out of parts that can't be found.  Perhaps one could
>build a linear VCO out of tubes that would respond to MS style voltages.

One could use current control like in my VTVCO, replaceing the expo convertor 
with a current mirror.

Bye,
 René






opinionsexpressedher   | uzs159 at uni-bonn.de
einarethatofmyemploy   | http://www.uni-bonn.de/~uzs159
erandnotofmyself....   | http://members.xoom.com/Rene_Schmitz