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DC13.8V to DC250V Inverter Circuit Diagram I have done a lot of work with valves in recent years. For me valves have many advantages, least of all the price; since they are now "obsolete" it is quite easy to get hold of them for next to nothing at rally's and junk sales. I recently purchased a couple of hundred battery valves for less than SEK1 (US$ 0.15) each. The biggest problem with valves is the PSU needed to provide +250 vDC and 6.3 vAC for the filaments. The transformers are no-longer available at a reasonable price, but a pair of 12v-6v-0v-6v-12v mains transformers will do the job just as well. For portable use only one transformer is required together with a pair of power transistors such as 2N3055 etc.

This ac to dc power supply can output 5A in continous operation and 12A peak current. This kind of dc power supplies uses a PCB so you can use two case types for IC1, TO-220 or TO-3. The regulation of this 12 volt power supply is made with TR1 ( multiturn ). IC1 must be placed on proper heatsink. LM338 Power Supply Circuit Diagram :

If you have trouble locating an 8-V regulator, although they are commonly available,a 5-V unit can replace it by connecting the regulator, as is shown here.     Simple 8V From 5V Regulator Circuit Diagram