In a book I have-Repairing Transistor Radios by S. LIBES
Riders (# 270)Chapter 9 ...The A.C. ripple content of a battery eliminator should therefore be checked with a calibrated oscilloscope... A good eliminator should have less than a 1-volt (peak-to-peak) a-c ripple.Since transistor power supplies require low voltage output, high capacitance electrolytic capacitors added to the filter system reduce the a-c ripple appreciably. Many so-called battery eliminators are unsuited to transistor power supply usage.-------------------------Here is an illustration of a PACO B-10 battery eliminator designed to power transistorized equipment. (ANALOG TYPE POWER SUPPLY)
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OF course you can use a switching power supply, with the
caveat of RF noise being broad-band and difficult to suppress. And most switching power supplies are not multilevel voltage select-able.
-----------------------They also mention that you can construct your own.Here are the parts needed.1. Silicon rectifier maybe a 1N4000 series ( I would modify that to be a bridge type - less problems with filtering.
2. Filament transformer (secondary taps of 1.5,3,5,6.3,7.5,12,20, 25, 30, 35,50 volts each) Similar to
Stancore P-1834-3 or a scavenged tube tester power transformer.
3. Switch for the primary (4 pole switch) switching from OFF
-1 125V
-2, 115V
-3, 105V
-4 4. 12 position Rotary switch ( to connect to each of the secondary filament winding's)
the center switch conductor path connects to the diode ,
5. a capacitor of 100ufd ,
6. a resistor of 3.3kohms,
7. and a 1000ufd 50v capacitor.
8. two output connectors (your choice of style) banana sockets, binding posts, or alligator clips .
the resistor is connected to both capacitors positive leads between them.
the capacitors are connected to the common transformer ground on the secondary.
two output connectors , one goes to the 1000mfd electrolytic + and the other to common secondary transformer ground.
I thought this might be a fun construction project for those on a limited budget.
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