It was just a caution John - as you have done you can fiddle with caps, resistors, inductors etc. etc. and come right. Nor was I suggesting that the battery was mandatory (that would sort of defeat the whole object anyway).
I often use a "wall wart" as a donor for the transformer & rectifier at the start of a more elaborate power supply.
The problem with equipment meant to run on a battery is that it generally has no surge protection etc. etc. and "expects" beautifully smooth DC. The guys who designed, built and debugged it made no allowance for ripple, surge and voltage variation - why would they.
Nothing wrong with the idea of replacing the battery - great idea in fact - but if you experience problems - first place to go looking would be the power supply.
Attached a simple circuit - the first part - transformer / rectifier / capacitor - is the donor "wall wart", the LM338 (or similar) is a 3 wire stabilised power supply to which you only need add the trimpot, resistor and two small caps to get flatline DC.
The last parts - 2 diodes and a resistor are for min. load, back EMF suppression and overrun voltage protection and can be ommited from non-noise generating loads.
I often use a "wall wart" as a donor for the transformer & rectifier at the start of a more elaborate power supply.
The problem with equipment meant to run on a battery is that it generally has no surge protection etc. etc. and "expects" beautifully smooth DC. The guys who designed, built and debugged it made no allowance for ripple, surge and voltage variation - why would they.
Nothing wrong with the idea of replacing the battery - great idea in fact - but if you experience problems - first place to go looking would be the power supply.
Attached a simple circuit - the first part - transformer / rectifier / capacitor - is the donor "wall wart", the LM338 (or similar) is a 3 wire stabilised power supply to which you only need add the trimpot, resistor and two small caps to get flatline DC.
The last parts - 2 diodes and a resistor are for min. load, back EMF suppression and overrun voltage protection and can be ommited from non-noise generating loads.
