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Quoth · 03-13-2025, 04:09 PM

The 742 is called an A battery, because it's for filaments, the A power rail. It's not an A size cell. Many different size packs from 1.5V to 12V were used for the A rail. This A (function) battery happens to be 1.5V.

The A size cell was smaller than a B Cell and larger than AA, and cylindrical.
A cell cylindrical mm = 49 high x 17 diameter. IEC R23 Znc capacity 2200mAH

The HT was called the B power rail. The 762-S is not a B size cell, which is 1.5V, it's 45V.

The GB or C battery was for Grid Bias. It is not a C cell, but was often 3 to 8 "B" size cells.

The USA used the terms A, B and C for the Filament, High Tension (HT) and Grid Bias batteries probably from 1920s. The A battery was 2, 4 or 6V before Sylvania developed the 1.4V filaments in 1938, then RCA miniaturised them in 1941. Then the A battery was 1.5, or 7.5V on a set that had series filament.

Later the names AA, A, B, C, D, E, F, G where given to basic single round cells in the USA, maybe in 1946 or 1947. They had maker specific names before that. Ever Ready in the UK used:
U7 = AA
U10 = B
U11 = C
U2 = D

A USA #6 was a UK Flag. An enormous round cell used for servant flag boxes, Railways, electric powered penulum clocks. The same size is used inside in the round Zinc-Air Fencer power pack (I forget if 5 or 6, 7.5V or 9V, agfes since I took one apart.). Some cars without dynamo and crank starter might have used a #6 to assist the magneto driven ignition during cranking. Acetylene based lamps!

A little knowledge is dangerous.
A D (UK = U2) or a pair of D in parallel was used in the 1941 "Lunch box" AKA "Personal Radios" that were made from 1941 to 1950s as the "A" battery.

The A size round cell, AFAIK, was never used in radios. Certainly in decades of restoring battery valve/tube radios, and researching old catalogues I never saw it.

Even for a torch the A cell was rare and I don't see any evidence it was used outside of USA. No UK or European equivalents found.

ALL the lettered Cells AAAA, AAA, AA, A, B, C, E, F, G are round (cylindrical). Most not used ofr radio. There is also an N cell AKA Lady, that is between AA and AAA in diameter and about 2/3rds length. I convert Electret mics to use two as the capsules are marginal at 1V to 1.6V (the regular cell) and are better at 2V to 3.2V (2 x N cells).

EDIT
Actually I see the Wikipedia page does mention that one of the Lithium cells is almost the size of an A size cell. The 18490 is maybe close, but of course totally the wrong voltage.

03-13-2025, 04:09 PM	#38
Quoth Still reading Posts: 14,379 Karma: 107076273 Join Date: Jun 2017 Location: Ireland Device: All 4 Kinds: epub eink, Kindle, android eink, NxtPaper	The 742 is called an A battery, because it's for filaments, the A power rail. It's not an A size cell. Many different size packs from 1.5V to 12V were used for the A rail. This A (function) battery happens to be 1.5V. The A size cell was smaller than a B Cell and larger than AA, and cylindrical. A cell cylindrical mm = 49 high x 17 diameter. IEC R23 Znc capacity 2200mAH The HT was called the B power rail. The 762-S is not a B size cell, which is 1.5V, it's 45V. The GB or C battery was for Grid Bias. It is not a C cell, but was often 3 to 8 "B" size cells. The USA used the terms A, B and C for the Filament, High Tension (HT) and Grid Bias batteries probably from 1920s. The A battery was 2, 4 or 6V before Sylvania developed the 1.4V filaments in 1938, then RCA miniaturised them in 1941. Then the A battery was 1.5, or 7.5V on a set that had series filament. Later the names AA, A, B, C, D, E, F, G where given to basic single round cells in the USA, maybe in 1946 or 1947. They had maker specific names before that. Ever Ready in the UK used: U7 = AA U10 = B U11 = C U2 = D A USA #6 was a UK Flag. An enormous round cell used for servant flag boxes, Railways, electric powered penulum clocks. The same size is used inside in the round Zinc-Air Fencer power pack (I forget if 5 or 6, 7.5V or 9V, agfes since I took one apart.). Some cars without dynamo and crank starter might have used a #6 to assist the magneto driven ignition during cranking. Acetylene based lamps! A little knowledge is dangerous. A D (UK = U2) or a pair of D in parallel was used in the 1941 "Lunch box" AKA "Personal Radios" that were made from 1941 to 1950s as the "A" battery. The A size round cell, AFAIK, was never used in radios. Certainly in decades of restoring battery valve/tube radios, and researching old catalogues I never saw it. Even for a torch the A cell was rare and I don't see any evidence it was used outside of USA. No UK or European equivalents found. ALL the lettered Cells AAAA, AAA, AA, A, B, C, E, F, G are round (cylindrical). Most not used ofr radio. There is also an N cell AKA Lady, that is between AA and AAA in diameter and about 2/3rds length. I convert Electret mics to use two as the capsules are marginal at 1V to 1.6V (the regular cell) and are better at 2V to 3.2V (2 x N cells). EDIT Actually I see the Wikipedia page does mention that one of the Lithium cells is almost the size of an A size cell. The 18490 is maybe close, but of course totally the wrong voltage. Last edited by Quoth; 03-13-2025 at 04:25 PM.