Transformers

[Cursitor Doom]

Or - as someone else suggested elsewhere, just use a 19V laptop PSU with one or two diodes in series in the + line.

[Paul]

You may be able to find a schematic somewhere. Whatever radio you've got.

The wiring you find at or near the battery bay, would indicate whether the thing was CT or not.

Since at least some of these, are AC coupled output (large electrolytic, bad news when the electrolytic fails short), they don't particularly need CT to work.

The instructions I'm finding, with a bias adjustment for "symmetric output" (which would be audible as distortion if you didn't have an oscilloscope), that strikes me as "danger material" and that tells you where the battery life is going. That's an adjustment required by certain classes of audio amps. Replacing that section with a modern equivalent (with very low offsets in stuff inside), would at least cut down on the quiescent power consumption. It's the totem pole conduction through the output stage, that is eating the battery for lunch.

Linear regulators are not exact replacements of batteries. Like an ATX supply, the output is "push only". If current were to flow back towards a linear scheme, the voltage rises on the output. There are only a few regulators which are push-pull and behave like ideal voltage sources. Batteries may not like sustained current flow back into them (any chemistry not rated for charging), but when an application calls for a little bit of AC current flow in and out of the battery, the battery is better at that sort of thing, than an LM7818.

Paul

[jon]

It's a Hacker with 18v supply no centre tap required.

[The Natural Philosopher]

Then series the windings and use two diodes.

[Peter Able]

No problem, then.

[Animal]

but not an issue with a 1960s radio

[Cursitor Doom]

Yes, it's straight 18V but that's not immediately apparent from casual inspection. The battery wiring 'implies' they're CT and one naturally assumes split supplies for a class B audio amp. I didn't twig that was incorrect until I'd obtained the circuit diagram for it.

[Peter Able]

Still no problem, then. My idea will deal with both circumstances.