I just want to say thanks guys for the clarifications. I think for the fun of it I'll be building mine with a through-hole kit. I just feel like I'll have more fun modding it, and it'll look older and cooler. :)
I have a BITX 20m v.3 PA PCB from the ebay shop of Sunil VU3SUA. It has two amplifier stages and two transformers. The description says it can be modified for 40m. But it does not say how.
How many bifilar turns on FT37-43 should I use for the driver and final transformers when I build for 40 meter / 7mHz?