Looks like a fun project, don't have one ... but I did go get the schematic.
I am a fairly experienced builder and maybe a second set of eyes can help.
Guess I can can ask the obvious questions and get away with it ... ;-0
Any chance there's a mis-populated part? For example, swapping C6 and C8 ?
Or a wrong value part at R1 or R2?
One of D3 or D4 backwards, or swapped with some other diode?
Then there is always the famous toroid-lead tinning problems in kits of this type.
If the center of the secondary on T2 isn't grounded....or one end of the secondary on T1...
Steve KZ1X