"The solution of this problem exists, and it is very simple (at least using vacuum tubes).
For commercial reasons i can't say the solution because I use it on my Pegna Satie Tube Theremins." - Pegna
This kind of BS really annoys me!
What is the point of saying "The solution of this problem exists" and then saying " i can't say the solution " ?
As for "commercial reasons" perhaps this MIGHT apply if there were hoards of tube theremin builders competing for the market - But there arent! .. In fact, if you were really selling tube theremins, you may nearly have the complete monopoly! - And with the size of the market, no sane person will jump in, nick your "solution" and compete with you! -
The market is so small that your priority should be supplying those interested in your theremins and communicating well with potential purchasers - not paranoia about some competitor nicking "your" idea which, according to you, has been in the public domain since the '30s.
Errr.... One question - your "technical problem" which prevents you supplying theremins and prevents you from even being polite enough to contact potential interested customers - it wouldnt have anything to do with "thermal issues" would it ? Perhaps you have a problem with hot air...
"Many people is blocked by theory before doing anything pratically. It's a common problem in DIY electronic."
IMO, a more common problem is that, due to lack of any theoretical understanding, people do some simple DIY project, cannot debug a simple issue to get this item to work, and give up - never to return to electronics. The other common scenario is hobbyists who through luck, do get their project to "work" - but then flounder in a murky theory-less world of garbage circuits they dont understand - spend years despising theory, and limit their potential for want of the discipline required to sit down with the books and gain basic understanding of electronics.
IMO, it is irresponsible to discourage people from learning theory - Any positive future is in the hands of those who understand, not in the hands of those who wallow in and glorify ignorance - One reason, IMO, for the awful state of the world, is the deliberate ignorance being promoted and to which the masses are subjected.
When I look at the abysmal education children and even college / university students recieve today, particularly in the sciences, it fills me with despair - I know one kid who just passed their science exam by reading past exam papers two days before the exam, and memorising the answers - this kid knows nothing - doesnt understand the questions, doesnt understand the answers - but got a great grade! - most of the questions on the paper were IDENTICAL to questions in past papers.
"and I'm very curious to know how you solved the technical problems I was talking about."
The way I solve the thermal drift problems are the "absurd" methods you talk about : " thermal correction, thermalinsulation, more complex oscillators design and so on "
Due to my topology, I tend to go to having "ovened" transistors in an array, and a thermal sensor on the board to compensate inductor / capacitor variation concequential to temperature.
The classic method (as employed, I believe, by Lev) was to use capacitors with +Ve or -Ve coefficients and tack these onto the tank or resonator until thermal drift was reduced to acceptable levels - having established the required coefficients, these capacitors only required minimum trimming on production.
The above is fine if one has a fixed build, its not economic in todays world as time taken to do "select-on-test" is costly - IMO, having a thermistor and a multi-turn trimmer (from which a correction voltage is obtained and used to trim the front-end capacitance) , putting the theremin into a "oven" (I use a modified Peltier refrigerator) , adjusting the trimmer at 15C, 25C, 30C so that the pitch (with a good NPO and tiny +TC capacitor to account for antenna thermal expansion replacing the antenna) stays constant at these temperatures.
Doing the above, and substituting parts until things were right, would take far too long - with a trimmer I can get the setting for the trimmer in 2 thermal sweeps - in fact, I can interrupt at any point and trim the preset if I see the pitch change - it still takes too long (about an hour) but I can be doing other things whilt this process is occurring..
If I ever got to producing dozens of theremins, the process could be automated with a motorised preset adjuster or by replacing the preset with a NV "digital" potentiometer or two.
I accept that using a tube-only theremin, it would be expensive to implement the above - You could do it with a thermistor, couple of opamps and transistors driving a tuning mechanism, but not easily with tubes!
My main reason for a "global" TC adjustment is that there are many factors which affect thermal stability - every component has thermal charactaristics, and in my designs there are a lot of components! - Every potentiometer, capacitor, inductor, semiconductor has some influence if they are in any way related to or influence the tuning..
By having a global compensation, all +Ve and -Ve themperature influences can be counteracted reasonably well without having to calculate the individual contribution of each part - and this also leaves one freer to make changes to the design without introducing drift as an accidental concequence.
Fred.
