Device transformer has 2 secondary windings one of which is used for heating tube cathodes. I decided to use this winding to make stable 6.3V so i could use it for heaters and for resistance measurement. I didn't want to put in D-cell every time and monitor its health. So lets see how my idea with stabilized 1.5V will work. So far i am waiting my PCBs which i ordered from JLC and they should come July 6. Then i'll start assembly and main checks