Akula 1W PNP biasing

[tru168]

Hi all,


Just saw Wesley's translate here:
http://www.youtube.com/watch?v=jVTKRLWAo_c
by carefully look at the circuit, here's my opinion about the design:
1)transistors need to be extremely high gain to oscillate by using a opened coil as feedback antenna.
2)The circuit need another capacitor around 100pF - 470pf to oscillate if using normal lower gain transistor.
3)The PNP transistor bias seems wrong. 


if PNP transistor bias corrected and capacitor added, although it can oscillate but not sure if it will give OU, I watched the video clip and found something weird at 1:31 , the LED blinks before the 3V battery touching the solder point.

[Marsing]

hi, where can i find the schematic ? 

[tru168]

Hi,


Here's the schematic, which already mentioned in others post quite sometime ago. Some one replicate it, but can't get it oscillate. I check on the schematic and found bias error for pnp  transistor. 

[Marsing]

Hi all,

Just saw Wesley's translate here:
http://www.youtube.com/watch?v=jVTKRLWAo_c
by carefully look at the circuit, here's my opinion about the design:
1)transistors need to be extremely high gain to oscillate by using a opened coil as feedback antenna.
2)The circuit need another capacitor around 100pF - 470pf to oscillate if using normal lower gain transistor.
3)The PNP transistor bias seems wrong. 


if PNP transistor bias corrected and capacitor added, although it can oscillate but not sure if it will give OU, I watched the video clip and found something weird at 1:31 , the LED blinks before the 3V battery touching the solder point.

thanks for the schematic. I will try to replicate it, can you explain point 2 about another capacitor  and point 3 about pnp bias.

IMO, from the schematic, (T1, T2, T3 = hfe is unknown and if L3 acts as usual winding)

T1 is always ON, except L3 pull all the current from the base of T1, it will oscillate, R1 values may have to be changed.

"although it can oscillate but not sure if it will give OU ".
agree with you for the moment.

[tru168]

Hi Marsing，




The T1 will bias from L3 and start oscillate, if hfe is high enough, or L3 pickup a lot of "signal" from other coils. I found that T3 don't have any bias unless it start to oscillate, I agree to tune some other resistors value to make it work nicely. I saw another version says the R1 value need to reduced to 100ohm. I will suggest to remove R3, and connect a 100K resistor from T3's B to -Ve, that will provide bias to T3 and will oscillate more easier.
as for feedback capacitor , If the circuit build correctly with enough gain, feedback capacitor actually not necessary , if poor coil is used, feedback capacitor of around 220pf need to be in between T1' C and T3's B. I will suggest to tune until it oscillate nicely without the feedback capacitor.


The design looks simple and fun to build, I will try to build it by this coming week end, just for fun.