Just built Etherwave doesn't work

Posted: 10/15/2013 9:59:36 AM
Ubermann

Joined: 10/15/2013

Hi all.

I've built my Etherwave theremin using my own layout and unfortunately it doesn't work.

I suppose the theme was discussed few times but I hope you would help me with my case.

 

All components are placed on one one-side circuit board with jumpers. Placements of components are approximately the same as in original factory-built circuits from Etherwave kits.

I found three schemes in Internet:

1) From "Build your Etherwave theremin" document 1996.

2) From official "Hot-Rodding your Etherwave" document.

3) From unknown "Hot-Rodding" document.

All three schemes have some differents. For example C12 on schemes 1 and 2 have value 1000pF but on scheme 3 it has 100pF.

Some time ago I built a theremin using scheme 1 and another layout. The circuit was workable.

And new theremin I built using scheme 2 or 3 is unworkable.

 

Of course I had problems with component searching. I couldn't retrieve any J.W.Miller inductors and the variable inductors instead in the original scheme. So I replaced it by another components. Changes are below:

2.5mH J.W.Miller inductor -> 2.2mH axial inductor + 330uH axial inductor (in real it's about 310uH).

5mH L9 and 5mH L10 -> 10mH axial inductor.

10mH J.W.Miller -> 10mH axial inductor.

100uH variable Toko RWRS-T1015Z -> Toko A7BRS-T1040Z with Q=80.

47uH variable L5/L6 + 47uH const L12/L13 -> Toko A7BRS-T1040Z with Q=80.

68uH variable Toko 154ANS T1019Z -> Toko A119ANS-T1043Z with Q=80.

47uH variable L11 + 22uH/33uH const L14 -> Toko A119ANS-T1043Z with Q=80.

LM13600 -> LM13700 (but this doesn't matter as I know).

 

To debug my theremin I have just multimeter and no oscilloscope at all. I tried to compare voltages between my new theremin which is unworkable and my old theremin which is built by scheme 1 some time ago. Looks like my new Volume Oscillator works incorrectly because voltages from bases of Q6 and Q7 are about 0 and voltage of their emitters is about +0.02VDC.

I checked the layout many times for few days and couldn't find any mistake. I suppose the problem is somewhere else.

I tried to change Q6,Q7,Q8 but it doesn't help. I tried to use C13,C14,C15 from scheme 1 because the Volume Oscillator should on any of three schemes should generate 470kHz frequency signal. And it doesn't help too.

As I can see by my multimeter the voltage on pin 13 of U3 is too small (about 0.03V) and almost doesn't change when I bring my hand over the volume antenna.

So I can't understand why the schemes 2 and 3 doesn't work.

 

QUESTIONS:

1) Could you please help be to find out the problem. Why my new theremin doesn't work? What's wrong with my Volume Oscillator?

2) What the scheme is correct, 2 or 3?

3) What the capacitance should be for C12? 1000pF or 100pF?

 

Thanks in advance.

 

Ubermann.

 

Posted: 10/15/2013 10:43:32 AM
Ubermann

Joined: 10/15/2013

I forgot to say an important thing.

When I jus