AETHERPHON, global theremin family

Just my particular setup. Probably something somewhere didn't gel quite right, wiring layout, who knows. 

However, excessive shunt resistance is a well documented phenomena for oscillator irregular operation. 

The schematic is on the kepptheremins yahoo group, and Marks original is on my site at

http://wwww.neidlinger.us/keppinger.htm



--- In aetherphon@...m, kkissinger@... wrote:
>
> Philip,
> 
> Is a schematic of the Keppinger theremin available?
> 
> Do all the oscillators have this problem or is it just your variable  
> frequency oscillator?
> 
> If you disconnect the oscillator from the detector does it oscillate  
> strongly?  One wonders if there is a leaky capacitor or something that  
> is robbing energy from the tank.
> 
> Normally, one expects the oscillators to couple -- is it possible that  
> instead of coupling they are phase-cancelling each other out?
> 
> I've not spent appreciable time with vacuum tube circuits however I'd  
> check the individual oscillators (that is, I'd deactivate all but the  
> oscillator I'm testing) and determine if the issue is with an  
> individual circuit or is some kind of interaction.
> 
> All the best... keep us posted.
> 
> -- Kevin
> 
> Quoting Philip <kmg5443@...>:
> 
> > When I was building my Keppinger theremin, I recall that it sounded   
> > wonderful. What was not wonderful was the issue that the oscillators  
> >  would not keep oscillating. I could momentarily restore function by  
> >  grasping the large coils. The suckers would work for a minute or so  
> >  and then quit. I believe the X factor, be it the transconductance  
> > of  the tubes or my own unique and extensive personal magnetic   
> > bio-field, somehow prevented my theremin from working correctly   
> > (perhaps an unrealistic expectation). Permanent dunking of the unit   
> > in the nearby Atlantic Ocean was almost realized due to engineering   
> > frustration on my part.
> >
> > I have a WW2 era tome, Radio Engineer's Handbook, by Frederick E.   
> > Termen, Sc.D. I wonder if he was related to Lev? Anyway, one of the   
> > items discussed under in oscillator chapter was that the time   
> > constant formed by the grid shunt bias resistor Rg and the coupling   
> > resistor Cg to the tank was important.
> >
> > The text stated that if intermittent operation of a Hartley   
> > oscillator is experienced, then reducing the time constant Rg x Cg   
> > may be helpful. In essence, the tank is not getting enough "kick" to  
> >  keep it running. The text also stated that the preferable method of  
> >  accomplishing the reduction was via decreasing Cg, and NOT Rg.    
> > Reducing Rg would change the bias operating point of the tube.
> >
> > The initial values were Rg = 100 Kohms and Cg = .001 uF. I had   
> > reduced Rg to around 80 Kohms and voila!, the sucker worked.
> >
> > Now memory being what is, I seem to recall that the theremin sounded  
> >  better when it was intermittent. I posit that my changing of the   
> > grid shunt resistance, not only shifting the bias point of the tube,  
> >  but also changing the tone of the instrument. In retrospect, I   
> > perhaps should have reduced the value of Cg. My napkin calculations   
> > indicate values in the neighborhood of 750 pF with the original   
> > 100Kohm shunt. Obtaining a variable cap in that value is not   
> > practical. So, one needs to tack solder a range of values from 470   
> > to 750 pF and see if the intermittent operation is cured and the   
> > sound is better. Mica caps in that size are cheap.
> >
> > My primary complaint has been lack of character in the tone, i.e.   
> > the waveforms closely resemble a sine wave at some points. The high   
> > frequency harmonic issue has been largely cured by careful selection  
> >  of the two oscillator frequencies so any mixing products are  
> > outside  the human range of hearing (i.e greater than 20 KHz), and  
> > careful  selection of the volume oscillator bias point. If the bias  
> > of the  volume oscillator circuit is advanced too much, i.e. more  
> > volume for  a given hand position, "fuzzing" of the tone at low  
> > frequencies  (approximately 500 Hz and lower) is noticed and is  
> > objectionable,  rather than what one would expect from pleasant  
> > overtones.
> >
> > I am a quintessential Electrical Engineer. I read this text while on  
> >  the throne at my day job.
> >
> > Opinions?
> >
> > Thanks
> >
> > Philip Neidlinger
> >
> >
> >
> >
> > ------------------------------------
> >
> > AETHERPHON, the global thereminist community
> >
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> >
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> >
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> >
> >
>