Good morning, I have a battery valve radio which utilises 2 volt filament valves, which collectively draw about 550 ma. Is there a simple power supply circuit that would provide the above? bowler

LM317 will go down to 1.25V Download a data sheet. Be careful some regulators like the 78xx series will not regulate if there is no load, or if loading falls below 5mA.

Some Solid State regulators also go berserk, if the out put is grounded.

Marc

I designed one many years back when I was into battery radios. Silicon Chip published it.

I still have PCBs and most parts for it.

It can do 1.5 or 2 volt filaments with a jumper change and it has 45v, 90v and 135v outputs as well as some negative bias voltages.
Unlike other designs, the A and B supplies are galvanically isolated (just like A and B batteries are) so there are no issues with back bias.
It will fit inside most battery radios.

The A supply is regulated, unconditionally stable regardless of load and short circuit protected. It can supply just over 1 amp, there is some 100Hz ripple if you try to pull more than that.
The B supply is not regulated, nor does it need to be. It behaves in a similar way to a B battery in that it has some internal resistance - pull more than 10mA from it and the output sags. So it can't destroy valve filaments if you wire it up incorrectly.

Email me if you like.