Sir AdhiWay . . . .
Combine all of the answers you already received and you will have solved the problem.
My only request is your confirming that the transformer core materiel that you used is of the ferrite family . . .as specified
*****. . . and that you are NOT trying to use a common silicon steel E-I core . . . . .since the shown resultant
primary inductance and resonating capacitance suggest of a 50-100k operating frequency . . . load dependent / sliding .
.....
***** . . . . . .
CHANGES . . .
On your drawn schematic erase the bottom left corner connection of the 12Vsupply ground (COLD) and the right sides AC line N ground (HOT) as the twain shall never meet !
Put an NPN emitter tail on the transistor.
At the left sides rectifiers, put in their . . . .mooooooooore than adequate 470 ufd filter.
Note that they are using an E13003, while you are using the EVEN heftier breakdown of the E13007 or / as well as its twin 2SC4416.
Sooooooooooo . . . . your 12 ohm smoked . . . . maybe opened . . .but did both transistors not short out C-E during that / those power ups . . . . or were you
quick to pull the AC plug ? and saved them ?
This is an appropriate time to mention that with FULL raw dc coming thru that 680K is enough hard turn on of the E13007 / or / 2SC4416 to create exactly what has happened to you.
BECAUSE ? . . . of incorrect /opposite polarity feed back at turn on from the 9 turn feedback winding.
Cross / swap its wires and see if that permits start up oscillation and makee workee-workee.
A Timely Technical Tip . . . . .
A . . . . 100 millisecond visual alert . . . . (As that's just about your fastest neuro-bio-mechanical response capability)
Put a LED and series current limiting resistor across that units 12VDC output.
(LED + ~1k resistor that you have already solved the polarity and wiring connections and pre tested on a 12V or 9V battery source.)
Now when you swap feedback polarity, upon then just powering up, if you don't see that test lite immediately . .
PULLA- DE- PLUG !
THAAAAAAAAASSSIT . . . .
73's de Edd . . . . . . .
As a w i i i i i i ld and craaazzzeee teenager, it was only when I bought an INDIAN motorbike, that I found out that adrenaline is brown.
( And flows from
BOTH proximal and distal orifices! . . . . . . . frequently . . . .
SIMULTANEOUSLY ! )
.