Dual-output batteries with a tap part way were pretty common at one time. Although it's easy to think of tube/valve sets as needing relatively high HT/B+ voltages, many of the low-signal tubes for battery receivers were designed to run on quite low voltages.

Some of the older sets used a separate grid bias, or "C-" supply, negative with respect to chassis. This could be either a separate battery, or incorporated as part of the main HT/B battery (although the grid bias section had negligible load on it).

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The wireless valve heaters ran off a separate 2v glass lead-acid accumulator, and before we got mains power in '52, I used to lug 2 of these 'occard lumps to the pub for charging each week.

I have one of those old, huge "Everything Within" household books from the 1930s which has a whole chapter on "wireless."

Those fortunate enough to have D.C. mains, it explains, can charge their accumulators by unscrewing the cap from a light switch and connecting the accumulator across the terminals so that the light acts to limit the charging current.

And how do you determine the polarity of the switch terminals? Why, you take two pieces of wire, drop them into a beaker filled with a vinegar solution, and observe from which conductor the bubbles rise.

Can you imagine the legal types at the publisher allowing them give advice like that these days? [Linked Image]




[This message has been edited by pauluk (edited 11-01-2005).]