Dr Ronald Stiffler SEC technology

[gyulasun]

Nick,

You can prevent frying your transistors in advance.  For the types you have on hand, first look up each in the data sheet for power dissipation, P_D, collector current I_C and collector-emitter breakdown voltage V_CEo.   And you need a heat_sink_mountable casing style too.  If you find P_D is higher than 1-2 Watts, I_C is at least 0.5A or higher and V_CEo is higher than 100 V, then your devices will not fry at the very first switch-on moments due to overvoltage breakdown or little later due to getting hot.  The parameter h_FE is the higher the better,  preferably be higher than 100.

If you plan to run such oscillators from supply voltages higher than  say 35-40V, then you would need at least 150 V rated V_CEo
transistors or rather 200 V rated or higher when you crank up the converter to the max 55 V. 

Thanks for showing the video, you have made good progress and surely gained more practice to light that LED board just by the very loose capacitive coupling. You may test whether the use of the green clip lead from the AV plug diodes could be eliminated by connecting the same point of the diodes to the negative (or positive) supply rail via a short piece of wire.
First the brightness may not be the same like with the clip lead wire but in this case you could use a trimmer or variable capacitor between the LED board back plate and the free end of your air core coil, maybe the earlier brightness could be restored by that (or maybe not, only tests can give answer).Okay on the use of the 47 uF electrolytic capacitor across the LED board wire outputs.  Probably the brightness will not change much when you try to measure the DC voltage across that capacitor by your voltmeter, it is good to know the DC voltage the LED board and the 2 diodes develop from the RF capacitive coupling.

I made a snapshop from your video on the circuit board. You mentioned to put in a resistor you think was less than a 100 Ohm: which is it, can it be seen in this picture? I assume you refer to the one I suggested to use in series with the choke coil in the collector, to reduce heat dissipation in the transistor? 

Gyula

[gyulasun]

Hi Erfandl,

Okay, thanks for showing the current measurement results.  As I indicated before I did not blame the validity of your previous measurement on the reducement in input current when using 3 crystals in parallel: with oscillators it is always a good practice to filter the supply rails when measuring DC input current or learn about DC input power.   
So the mistery remains why the input current reduces and the brightness increases.
I think you have a 3rd 1000 uH choke coil available, right? Would you put this 3rd choke in parallel with the collector choke coil ? First do it with a single crystal and watch input current and brightness when you plug in the 3rd choke, then do the same when the 3 crystals are plugged in again. By the way, what is the resistance of such chokes? You can measure it with your digital multimeter when they are not plugged into the circuit.
With the parallel connection of two chokes in the collector I do not expect anything fancy would happen, just a suggestion to learn on its effect if any.  What you found as good by using the Pi filter is now there is no need for the use of the ferrite rod... 

You wrote: "DC DC boost converter pull 3.4 mA from battery !!!"

Would you tell what is the battery voltage you use to drive the boost converter?  And what is the output voltage you set the the converter to?  Just wish to know whether the 3.4 mA is a typo instead of say 34 mA ?

Thanks,  Gyula

[gyulasun]

Hi Itsu,

Okay, I understand and agree, no problem.  Thank you for doing all these tests and spending on the transistors too.  We all learn.

It is good you tested connecting 3 crystals in parallel. However if you found the output remains the same, then that is different from that of Erfandl finding: his brightness increases with using 3 crystals. 

You also found though that the input current decreases a little as in Erfandl's oscillator.  It is very possible though that with such 2-3 mA or so small input current reduction the brightness may be invisible small too, this can explain you found the output unchanged.

EDIT:  It occured to me that crystals have a parallel capacitance across their wires or pins which is measurable by a pF meter only because the capacitance value is around  3 to 5 pF.  If 3 such crystals are connected in parallel, then these values add up to anywhere from say 9 pF to 15 pF of course.   This may already have an effect in the oscillator circuit: this capacitance appears across the base and the collector and can influence feed back. 
From this it comes that if a trimmer capacitor of max 15 pF value is connected in parallel with the single crystal working in the oscillator, then it may have the same effect?  It may not justify such results but 3 crystals certainly have 3 times as high self capacitance... 

Thanks,
Gyula

[itsu]

Gyula,

concerning the output of my 3 crystal setup, i measured it with my scope (3 turn on toroid) and it did not
raise the output on the scope (looking at it on a tenth of a volt range).


But i was able to retune the variable cap / base trimmer pot for more output / more input current after
adding a new crystal, so there is some change in the tank / resonance circuit.


By adding a series trimmer cap to the crystal, one can change the crystal frequency a bit, so probably the
parallel capacitance added by extra crystals will change the resonance frequency also a bit needing a retune for
max.


Itsu

[gyulasun]

Hi Itsu,

Okay, thanks.  I agree with what you wrote on connecting a capacitor in series or in parallel with a crystal.

I was thinking on again whether my thought on adding a trimmer cap in parallel with the single crystal in the oscillator to mimic the capacitance of 3 paralleled crystals is a good one or not: because we run the crystal in an oscillator the trimmer cap should have more drastic (negative) effect between the collector-base points than the capacitance of the 3 crystals i.e. the trimmer cap cannot really mimic the role of 3 crystals. The trimmer cap does not possess the other properties of the crystals like a series LC circuit too, (besides the parallel LC) each crstal has.

With the three crystals, the harmonic spectrum may change and become reacher but because the crystals are surely within maximum some hundred Hz from each other, the spectrum lines could be seen quasy as a bit fatter, thicker at every harmonic spots. To see the 3 vertical lines at say the 3rd harmonic, you would need to expand, stretch out the horizontal frequency axis of the analyzer to see the 3 lines at that harmonic where so far there was only one vertical line. At the 5th harmonic the 3 vertical lines may get a bit further away from each other so they could be seen easier and so on.  This is because 3 crystals (running at nearly identical frequencies) should have three spectrum lines at the spots where a single crystal has only one line, this is so at each harmonics of course.

The increased number of harmonics in this sense may explain why Erfandl found an increase in the brightness when he used 3 crystals. We need to notice he does not have a resonant tank in the collector so all the harmonics may have higher amplitudes hence all can contribute to increase brightness a little. But there remains the question why the input current decreases with the 3 crystals?

Gyula