B Battery Takes a 9V Cell

Old American radios (and we mean really old ones) took several kinds of batteries. The A battery powered the filaments (generally 1.5V at a high current draw). The B battery powered the plate (much lower current, but a higher voltage–typically 90V). In Britain these were the LT (low tension) and HT (high tension) batteries. If you want to rebuild and operate old radios, you have to come up with a way to generate that B voltage.

Most people opt to use an AC supply. You can daisy-chain a bunch of 9V batteries, but that really ruins the asthetics of the radio. [VA3NGC] had a better idea: he built a reproduction B battery from a wooden box, some brass hardware, a nixie tube power supply, and a 9V battery (which remains hidden). There’s also a handful of zener diodes, resistors, and capacitors to allow different taps depending on the voltage required.

b-battery-in-useThe project looks great. The wooden box apparently was a recycle item and the brass hardware makes it look like it belongs with the old radios it powers. This is a good example of how there’s more to vintage restoration than just the electronics. Sure, the function is important, but to really enjoy the old gear, the presentation is important, too.

Not all tube radios took 90V B+, but since this battery has taps, that isn’t a problem. The old Radio Shack P-Box kit took 22.5V. Of course, if you are going to build your own battery, maybe you ought to build your own triodes, too.

21 thoughts on “B Battery Takes a 9V Cell

    1. At first glance, yes you’d think that’s a problem… but I made a nice little dual-triode regen set that runs on 12 to 16v, and I used a modified car cellphone charger (which is a switching DC converter) to drop the 12v to 6v for the tube filaments… and it’s no noisier than when I used a good bench supply for the filaments. Apparently there’s not many harmonics up into the MF broadcast and HF shortwave bands.

  1. My lord. Boosting a 9V battery to 120V, then regulating with Zener diodes to 88V through a 3k3 resistor? That circuit is going to try to suck 200 mA out of that 9V battery. The battery voltage is going to collapse fast.

    The only thing saving it is the low-voltage performance of that supply, drooping its output voltage once the input drops below 9V.

    A happy circumstance of two awful bits of engineering cancelling each other out. Still likely to get only a couple of hours out of it though.

      1. 10 mA is correct: simple arithmetic tells us the supply is providing 10 mA at 120V. Or 1.2 watts. With the claimed 65% efficiency of the supply providing that 120V from the 9V battery, that’s around 200 mA being sucked out of the battery…

  2. As a child, my father told be about the various sizes of batteries (cells) and he mentioned one called a “BC”. He claimed it was called that because it was the “size of a beer can”… In the years since then, I can’t find any reference to this size, and I now believe he was making it up, or he may have been talking about a #6 screw-top.

    Any thoughts?

    1. Oh, man, I’d forgotten about the #6 size. When I was a kid we had telephones that still used them (yeah. we lived in the sticks, a little behind the curve) , and they were great for powering the glow plugs on model engines.

      The central carbon electrodes were huge — made great electrolyser electrodes.

    2. The ‘BC’ part was that for a short time there was a terminal on some of these 90 V batteries (a tap as it were) to supply the 4.5 V that would otherwise require a separate ‘C’ battery.

    3. I think it must have been a regional thing and was likely only used by a small number of manufacturers.

      I have searched long and hard but not found a picture or reference to ones I saw.

      They were rectangular and about 2″ x 1.5″ x 6″ (5 x 4 x 15 cm) and had a three pin socket at the top. I am in Australia.

  3. I’ve got a 1920’s homebrew single-tube regenerative that was intended for batteries, but nowadays runs from an AC-connected supply. I’ve been meaning to build a little boost supply using a Li-Ion pack and USB for charging. Filament supply is 2V (intended for a single-cell lead/acid battery, these are still available) and I think we’re running B+ at 45V based on the tube’s datasheet.

    1. Well not quite, depends on a host of factors.

      Remember the “one hand in pocket safety rule” but, which I found doesnt work at 300V DC despite
      insulated floor, rubber soled boots – got a tinkle AND the screwdriver neon light came on full bright !!!
      Suggested max for safety in that respect is 48V DC however, if you wet your hands and grabbed a
      pair of metal spanners (high surface area, highest conductivity) and touched each to the terminal
      of a 12 V car battery (engine not running so no spark volts etc) – you will feel a tinkle often up to your
      elbows – so not recommended for anyone with a heart risk or a pacemaker etc It just goes to show
      even at 12V DC there is enough current to feel if the contact area is high with lowest resistance ie Wet.
      Edit:
      Obviously this is NOT crossing the spanners so as to draw current *between* terminals, remember ghost busters “dont cross the streams” yah hear ;-)

    2. because the terminals are inside the radio during normal use, and people who dont know how to work safely with high-voltage would not even dare touch. ALL TUBE RADIOS CONTAIN SCHOCK, (execpt the ones with a 22.5v B+ but those were rare) SO THEY KNEW THERE WAS A DANGER.

      remember, at first, ALL (residential) radio’s were battery operated BUT NOT PORTABLE, and costed several month’s pay. NOBODY knew squat about electricity because they didnt have either electric-service or did not own any flashlights, so they never looked inside, there was no battery-low indicator so they brought it to a service shop and got a 1hour lesson on everything, including safety.

      after the invention of the INDIRECTLY-heated cathode which allowed operating tubes from wall power, and the electrification of the country, radios became cheap and affordable for almost any middle-class family to own (one).

      due to cost reduction and need to sell batteries, portable units came onto the market.
      by the time people saved up for a SECOND RADIO (oh man), they were already familliar with the dangers of electricity because thier first radio (plugged into the wall) had a HOT-CHASSIS and as soon as the damm adjustement knobs fell off, and your hands were wet, you got a schock and YOU REMEMBERed not to muck around with stuff you dont understand.

      so when the battery died in someone’s battery-operated (non-portable) set, they either got it serviced, or took a short free lesson from the radio/battery shop. and if this set was a newer portable, they already knew not to touch the terminals.

      my opingion, mixed with fact.

      PS: a serious word of advice; when “rolling” button cells into 67.5v batteries, you will need to apply loaded force and affix (with tape?), this force is to maintain electrical contact, WEAR INSULATED GLOVES when pressing on this 67.5v “pile”, otherwise the excessive force due to minor electric schock will rip your “battery-rolling-paper” and they will scatter and fly EVERYWHERE! true story.

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