An Electronic 90V Anode Battery

One of the miracle technological gadgets of the 1950s and 1960s was the transistor radio. Something that can be had for a few dollars today, but which in its day represented the last word in futuristic sophistication. Of course, it’s worth remembering that portable radios were nothing new when the transistor appeared. There had been tube radios in small attaché cases, but they had never really caught the imagination in the same way. They were bulky, like all tube radios they had to warm up, and they required a pair of hefty batteries to work.

If you have a portable tube radio today, the chances are you won’t be able to use it. The low voltage heater battery can easily be substituted with a modern equivalent, but the 90V anode batteries are long out of production. Your best bet is to build an inverter, and if you’re at a loss for where to start then [Ronald Dekker] has gone through a significant design exercise to produce a variety of routes to achieve that goal. It’s a page that’s a few years old, but still a fascinating read.

A problem with these radios lies with their sensitivity to noise. They are AM receivers from an era with a low electrical noise floor, so they don’t react well to high-frequency switch-mode power supplies. Thus, the inverters usually tasked for projects like this are low-frequency, at 50Hz as this is a European project, to mimic one source of electrical noise that would have been an issue for the designers in the 1950s.

We are taken through transformer selection and a variety of discrete inverter designs using multivibrators, investigating how to maximize efficiency through careful manipulation of switch-on and switch-off times. Then a PIC microcontroller design is presented, and finally a CMOS ring counter.

The final converter is mounted in a diecast box and covered with a printed card shell to mimic a period battery. If you weren’t intimately familiar with battery tube radios, you might mistake it for the real thing.

We’ve featured one of [Ronald]’s designs before, though only in passing. His Nixie PSU was used in this rather frightening clock with no PCB.

46 thoughts on “An Electronic 90V Anode Battery

    1. Exactly! And even funnier is the battery he has a picture of is called a layer battery.

      Taking this one step further, if you can find a 9V battery that has the zebra type internal construction inside you might be able to literally stack them together, doing a good job of simulating the internal construction of the original battery.

    2. “Ever heard of daisy chaining 9v batteries?
      10 of them chained = 90v enough for most tube radio circuits”

      Though the available current will be very low, due to both the terrible power density of the 9V battery and the fact that we’re talking about 60 1.5 V elements in series (A 9V battery contains 6 very small cells), exactly like some of the old 90V batteries (two layers of 6×5 C cells, all in series were those I used as a kid in early 70s) , but with much higher internal resistance.

      1. filtering an SMPS is relatively easy, i have used boost converters on far more sensitive RF projects
        A well filtered dual phase synchronous boost inverter can have switching noise of well under -50dbm with several amps of draw for very little money and a very low part count
        but for this application a simple LTC3813 or LM5122 with some basic filtering would work fine

          1. with a shielded case EMI should not be an issue, if you happen to have internal EMI (should not be a major issue with this type of converter) a sheet of copper covering the filters will all but eliminate it

            i have used switching supplies for RF stuff for years, worse case you create a 100v switching supply and a 90v linear regulator if you really need switching noise below -75dbm (40uV)
            but there is no chance this radio is that sensitive to pick up anything around that

      2. An LC filter will take care of that. Have a look at RECOMs “Book of Knowledge”, I did a low noise analog front end design that needed a switch mode isolated DCDC recently and the simple equations and diagrams in that book really helped. The book is free after you register on their site.

      3. Since most of these radios were AM broadcast band only (540 to 1600 kHz), it should be possible to make a switcher that runs ABOVE the radio’s operating range, putting most of the noise out of it’s reach.

  1. Better off in my way of thinking just to make a simple shunt regulator with an 87v regulator tube (acts like a zener diode, only better). An isolation transformer would still be necessary to insure that the radio didn’t kill anyone, of course.

  2. I found one of these radios when I was younger. I was poking around and couldn’t believe the 90v sticker. I tried going to the library and look up old batteries, ” this was pre-internet days”.I couldn’t find anything about this, therefore I just took this as a typo. I tried hooking up a 9v to it but it just had these weird spring clips. Undeterred I wired that little bad boy in….. Nothing! I just gave up wondering why they had such a large space for one little 9v. It wasn’t until years later when I was surfing the ,WorldWideWeb! That nagging little thing never left me and I looked it up one day on some Geocities site. Lo and Behold there it was. A history of old batteries. I did finally figure out I would have never gotten that thing working, but curiosity was finally sated. Sometimes it takes years to learn the answer to something but I appreciated the ride.

    1. 90V, yah… wider spaced contacts than a 9v and 10″ high but looked same otherwise. It was the early 60’s, grade school. I had one at school for an NE2 flasher thingy demo. 6th grade. Buddy familiar with 9v on tongue and too much personal bravado (no… there’s another word for it) … he grabbed it and…

      … I got three days off just for having it at school. Science fair didn’t matter.

      Farther back you go the more common the higher voltage batteries were. It was still the tubes days, albeit pin tubes, but on their way out. The battery involved was my own purchase at Tandy/Radio Shack, a place you could go to find a tube tester and fix near any tv by pulling all the tubes and testing them, then buy replacements. Later years they carried VCR belts too…

      Come to think of it… farther back you go… the more there was…

      Nothing compares to what my Dad said they could get from a hardware store at 15 to play with. Got a tour of the sites and damage still obvious. You instantly go to jail for his stuff now. In my kid days it was my buddy up the street, his dad was a Chemist with a basement full of stocked shelves that city hazmat crews had to deal with 10+ yrs after we were long move out. Buddy and me hadda blast. It was our model rocketry days, but am off topic much too far now…

      I’ve diverged a by a WIDE margin… so stop. But it was fun! Thank you for the rememberances!

  3. An Eddystone box forsooth! I built a copy of a Quad 405 stereo power amp in a big one of those back in the day. Also a couple of transistor pre-amps to feed valve power amps for my Rickenbacker 4001S bass. What fun drilling holes and making sure that the wrong wires did not touch the case.

    As to this hack, I remember those 90V batteries back in the 60s, and having to cycle about 20 miles into Leeds to buy new ones.

    1. the current high voltage battery packs for flashes puts out around 320 volts, they are used to charge the flash capacitor quicker than the internal electronics and bypass the internal charging electronics.

        1. they are basically just converter driven, the power source varies, everything from old lead acid to lithium, most include a fairly beefy capacitor, if they do they often function from mains as well and can really boost the speed of a flash unit, some even include variable voltage PSU’s for powering various gear; cameras or continuous lighting etc.

          these are all for the small speedlight type flashes, the power packs for studio flashes are usually closed proprietary systems, i gather that the voltages and architecture there is very different, some use pulse forming many research lasers can only look longingly at.

  4. Battery tube radios did not have a significant warm up time. The tiny tubes have a directly heated cathode which warms up as quick as a incandescent lightbulb.
    To save battery power, battery powered transceivers switched off the filaments of the output tube(s) when receiving.

      1. “Rare knowledge nowadays. Betcha you also remember from TV; “Francis the Talking Mule” as well as the phrase “Spit in the back and whomp it one!”
        The phrase being from “No time for sergeants” Starring Andy Griffith”

  5. “A problem with these radios lies with their sensitivity to noise. They are AM receivers from an era with a low electrical noise floor…”

    The big reason was there wasn’t as many high power stations back when these radios were made, so they had to have increased sensitivity. While there were most of the same Clear Channel stations then as we have now, if you didn’t live in a major metropolitan area (which were smaller and fewer) then your local station were lower power. That’s why these radios had terminals for external antennas, and for a lot of people those antennas were big. Ferrite rods back then just couldn’t cut it, you had air loop antennas instead.

    Another reason for increased sensitivity was the fact that the bandwidth was way wider compared to our modern 10kHz, or kc for that time period. Some stations these days have even smaller bandwidth.The AM stations back then had WAY greater audio fidelity because of this. After all, it was the only method of reception and music was still big on the air. Today’s radio stations, with their narrower bandwidth are way more susceptible to natural and mandmade electrical interference. Ask anybody who grew up in the 40s and 50s what the sound of modern AM is compared to when they grew up. Current listeners have been cheated by this, and explains why talk radio is the main format heard on AM these days.

    So basically, you mostly have to use battery power for those radios which can. Mains power picks up noise over the lines, and PLC just adds to the reception problems.

  6. I do recall when my older cousins had portable tube radios power by batteries. I had on family member give me the portable radio he had while he was in the US Army. A tube time radio that could operate off batteries or 110 VAC. AM broadcast band and some of the shortwave bands. I used it in the warehouse of the independent oil producer I was working for when I became seriously ill and disabled. Sadly I lost track of that old radio.

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