Retrotechtacular: Remembering Radio Shack P-Box Kits

If you are under a certain age, you probably associate Radio Shack with cellphones. While Radio Shack never gave us access to the variety and economy of parts we have today, they did have one thing that I wish we could get again: P-Box kits. The obvious questions are: What’s a P-Box and why do I want one? But the kit wasn’t to make a P-Box. P-Box was the kind of box the kit came in. It was like a piece of perfboard, but made of plastic, built into a plastic box. So you bought the kit — which might be a radio or a metal detector — opened the box and then built the kit using the box as the chassis.

The perfboard was pretty coarse, too, because the components were all big discrete components. There was at least one that had an IC, but that came premounted on a PC board that you treated like a big component. One of my favorites was a three-transistor regenerative shortwave receiver. In those days, you could pick up a lot of stations on shortwave and it was one of the best ways at the time to learn more about the world.

On the left, you can see a picture of the radio from the 1975 catalog. You might think $7.95 is crazy cheap, but that was at least a tank full of gas or four movie tickets in those days, and most of us didn’t have a lot of money as kids, so you probably saved your allowance for a few weeks, did chores, or delivered papers to make $8.

The Dirty Few Dozen

The kits changed over the years. In 1975 there were twenty of them, but over the years there were about thirty different kits. In fact, the shortwave radio was a few bucks more than most of them, although there were a few that were even more, but — in 1975, at least — none of them were over $9.

The kits all had a few common features. You were told to use your soldering iron to make holes for the things like pots. Made a mess of your iron and also released oh-so-wholesome fumes. There were little aluminum terminals used for off-box connections. You can see them in some of the pictures above. They had springs that you would push down, insert a wire, and then the spring would clamp the wire.

If you want to see all the kits, there is a site with scans of many old Radio Shack catalogs. This page and the next one are where I pulled the data for 1975. But there are other years, too. There were also other kits that didn’t use P-Box, including a bunch of PCBs for a buck or two for projects like power supplies and stereo preamps. That didn’t include other parts though, but — of course — you could buy them all at Radio Shack.

And Today?

It is true you can get lots of beginner-level kits today. But many of them have tiny components, ICs, or rely on some complicated “magic chip” (a preprogrammed IC). These projects were simple and useful and inexpensive.

They were also available. Heathkit, for example, had great kits with amazing manuals. Sure, they cost more, but they generally looked like something you bought ready-made if you built it right. On the other hand, the cheapest shortwave receiver in a 1976 Heathkit catalog was nearly $70. Sure, it looked like a real radio and probably performed better, too. But $70? Might as well have been a million for the kids buying P-Box kits.

Even if you had the money unless you lived near a Heathkit store — there were a few — you had to order something and that was a lot harder and took longer without the Internet. You probably sent a check, waited for it to clear, and then waited for the parcel to arrive. Maybe you were smarter and got a money order or placed the order COD (cash on delivery), but it was still going to take time.

Radio Shack, on the other hand, was right around the corner. Well… about 30 miles around the corner for me, because I grew up in the sticks. But it was very likely you lived within an hour’s drive of a Radio Shack. You could take your birthday money, go to the store, and have near-instant gratification. That counts for something when you are a kid.

Rebuild

If you wanted to build your own version of any of these kits, the Sparktron website has scans of most of the manuals. The handily have a schematic and a bill of materials for each kit in the manuals, of course. Usually, the parts list was with the layout that showed you where to put the parts. You might have to cross reference some Radio Shack part numbers, too. Here’s the schematic for the FM radio, for example.

None of the kits were very complicated as they were meant for a kid to build in one or two sittings. Some of the parts might be a little hard to find, these days, but we’ve seen people manage.

The real question is what to build it on? You could use a piece of real perfboard, of course, but that seems like cheating. It would be near sacrilege to produce a PC board for them. It seems like it would be worth at least trying to make the perfboard red, as [Netzener] does (he’s rebuilt at least three P-Box kits in the modern day).

I’m afraid I don’t have any of the half dozen P-Box kits I built back in the day. But [robssk885] has one and he shows it off in the video below. If you want to see more, there is a gallery of contributed photos on the Sparktron site (towards the bottom).

76 thoughts on “Retrotechtacular: Remembering Radio Shack P-Box Kits

    1. From the manual:
      In this circuit, transistor Q1 operates as a superregenerative detector. With no signal present, pulses of current flowing from the collector circuit of Q1 establish an average value of collector current. When a signal is received, the pulse frequency changes, causing the collector current to vary at the audio rate. The resulting audio signal is coupled through audio transformer T1 to the base of transistor Q2 where it is amplified. Capacitors C8 and C9 in the audio amplifier stage help to filter some of the high-frequency hiss which would otherwise be objectionable for extended listening.

      From Wikipedia:

      The superregenerative receiver uses a second lower-frequency oscillation (within the same stage or by using a second oscillator stage) to provide single-device circuit gains of around one million. This second oscillation periodically interrupts or “quenches” the main RF oscillation.[38] Ultrasonic quench rates between 30 and 100 kHz are typical. After each quenching, RF oscillation grows exponentially, starting from the tiny energy picked up by the antenna plus circuit noise. The amplitude reached at the end of the quench cycle (linear mode) or the time taken to reach limiting amplitude (log mode) depends on the strength of the received signal from which exponential growth started. A low-pass filter in the audio amplifier filters the quench and RF frequencies from the output, leaving the AM modulation. This provides a crude but very effective automatic gain control (AGC).

      Superregenerative detectors work well for wide-band signals such as FM, where they perform “slope detection”.

  1. I know it was bound to happen, but it’s a shame that the “new maker movement” that began 20 years ago has shifted from making things from discreet parts to buying a few pre-built modules from Sparkfun or Adafruit and plugging them together.

    1. I’m going to argue that that’s not quite a fair complaint in that discrete parts still exist and people still make things from them, but the plug-togethers are a good, simple starting point to get many people interested enough in the results to pursue the rest into the more frustrating and arcane avenues of experimentation. This was the putative aim of the RS box kits after all.

      Also the discrete parts themselves have changed – if we could have gotten our hot little fists on things like an ATTiny/Arduino/Pi we would have in a New York minute. As it was, op-amps, 555 timers etc. were available and used for these kinds of projects and probably got the same complaints (“why aren’t they using individual semiconductors?”).

      1. Agreed. I grew up in that “P-Box” era when we were mainly using discrete components plus maybe a few analog or digital ICs. I still like doing stuff with discretes (including tubes), things like regen radios, preamps, etc… but I also have a small stockpile of Arduinos, ESP8266s, and other assorted modules and I really enjoy creating stuff with those too.

      2. Also today’s plug-together components are often at a much higher level of functionality than would be practical or even possible with discretes, significantly raising the level of projects that can be built for a given investment of effort and money.

        1. It’s much better today with all these ready modules. Children are getting so much more understanding than their children will in 20 years ;-)

          Sorry but I’m with Thinkerer – functionality is the key here.

          1. I work with university students in an Electronics Engineering program and can tell you that this is 100% incorrect. Students think you need an Arduino to blink an LED, and that engineering consists of copying a Fritzing schematic and downloading code from GitHub. Very few who identify as electronics enthusiasts can identify basic components and only a handful can calculate voltages, resistances or capacitance. The modules are not an aid to understanding they are a hindrance.

    2. You could say the same thing about kits back in that area using prebuilt capacitors/inductors/batteries/bases/transistors etc. Everything is made of smaller parts, and gatekeeping “you didn’t build this out at the molecular level” kind of thing is not helpful.

    3. So what?
      I would have killed for a shoebox with $30,– worth of Aliexpress modules when I was a teen.
      The stuff you can do with an ESP32 or even an Arduino UNO – while mainly focussing on coding and not debugging giant analog circuits that cost you your last penny as a kid.

  2. “The real question is what to build it on?”

    I’m a little confused about the originals. Did those boxes use regular perfboard material as their tops? If so then of course you would use perfboard! If you can’t find perfboard with those big, widely spaced holes then I guess you might find a board with no holes and drill them. I’d use a CNC for that in order to get the positioning perfect and to not go insane drilling so many. I would imagine that even a 3d printer with a dremel attachment could do that job.

    In the photos it almost looks like a molded piece of plastic. Is that what it is? If so then I see a future OpenSCAD project. 3d printed plastic of course would melt under a soldering iron but you might get away with it if you are fast. and careful. It helps if all the solder joints are on the under-side where a little bit of melt marks might not be seen.

      1. I’m not one to discourage people from 3D printing things at will (I do it regularly) but surely there is a more efficient way to come up with a plastic box with some holes in it.

      2. Yes, I was considering 3d printing one. The nice thing is you can add the holes for the pots instead of burning them with your soldering iron. Or scale the overall design to just the size you need.

      1. Yes, it melted like butter, but gave off particularly acrid smoke when heated. Sounds like polystyrene. Very easy to end up with holes that were too big or not round. I recall dreading that part.

  3. When I was 10-12 I built half a dozen of them, and the only one I recall working the first time was the night light. Why not? I had no education in electronics, no test equipment, and no mentors. If I put a polarized cap in backwards, or a diode, or swapped two resistors then it wouldn’t work. So I’d double check and triple check my work and eventually I’d figured out my problems most of the time, but there were a couple, like the “light beam communicator”, I never got working. Still, it was magical.

    1. The same thing happened to me, at age 10, except I bought parts for the projects. The first few didn’t work, and in retrospect, I knew so little that I would take the magazine literally, so if the coil I bought at the store was different, I’d not know if the pinout was different, same with the transistors. My soldering was awful, but I didn’t know that till later. And I had no troubleshooting skill.

      Ironically, things started working when I used parts taken off scrap boards. I knew more by then, so I had a certainty about some things.

      Michael

  4. One thing I absolutely miss about the loss of Radio Shack, even in this day of Internet ordering, is if I find myself short of some small, cheap component, I could run down to the store and have a good chance of getting some same-day, with no extra shipping charges.

    1. Yeah… that’s why it’s useful to build a small inventory of common stuff, and also to grab discarded electronics when you can and steal parts from that. Though it’s near impossible now to salvage useful stuff from modern surface-mount PCBs…

      1. I don’t think Radioshack was good at all for building an inventory of anything, even a small one. My experiences with the Rat Shack do begin around 1990 though. The “older oldtimers” make it sound like it may have been a whole lot better in the 70s. A soldering iron might have damaged my mother’s womb so… I guess that was out for me.

        Anyway… if your project is stuck waiting on a part and it was a common one then yes, RadioShack was great for that! Why would you ever stock up there though?!?! They sold specific parts in blister packs of 1 or 2. ! or 2!!! Those blister packs cost as much as a baggie of somewhere from 10 to 100 off the internet.

        They did have a little value in their variety packs. Their resistor variety packs may have been ok, not great but ok. Their electrolytic variety packs were expensive. I bought a transistor variety pack and most of them had no markings! Likewise for an inductor variety pack. Their ceramic disc variety pack had those ambiguous markings where the last digit may be a power of 10 or it may be the ones place. Do you know what transistor, inductor and capacitor testers cost in the early 90s? Do you know how much that is in “kid who occasionally gets an allowance dollars”?

        If you want to build an inventory then my recomendation would be a hamfest. It’s cheap like the internet but you get to be there in person, see touch, feel, taste (ok, don’t do that) the merchandise in person. Best of all, if you don’t mind doing some manual sorting (ok a lot of manual sorting) there is a very good chance that somone will give you a large box full of components for free. That’s right, FREE!

        Or, if you just want to make it easy on yourself. Pick the values plus quantities you want and it’s all labeled and sorted already for you then just use the internet. I know there is a lot of concern about counterfeit parts but when it comes to the super common stuff, passive components and semiconductors that have had good generic available since before most of us were born… even FleaBay is pretty safe and if you can wait (and wait and wait) for it it’s pocket change. You might want to aim a little higher for your more advanced semiconductors like micorocntrolers, serial to usb converters, etc… Not that high though. Dx.com perhaps?

        Believe me, I lament the fact that real world, physical locations that I can go to shop for parts are so rare and far away now. I do value stores and I do get that they have to charge more due to overhead. RadioShack though.. at least in MY lifetime… their prices were bat shit insane! It is no wonder that they didn’t make it. So long!

        1. I bought some OP-amps one time, but paid a premium to get them when nothing else was open. Radio Shack’s prime was probably the late sixties, bought by Tandy they were expanding and right when transistors were taking over. They’d basically print a catalog ever few months in Elementary Electronics, all kinds of neat stuff. But that was before they had stores on every corner.

          By the time they came to Canada, I’d found the local parts stores, so Radio Shack was always “too expensive” though maybe some of that was being in Canada. They were a great source of some interesting parts, especially when on sale, and maybe the next year when they were clearance items. But yes, they lacked completeness, even if the prices had been better. They had cheap books, often rebadged from other publishers, so I’d buy those. I got lots of tools at Radio Shack, something easy to ask for at birthdays and Christmas, or again when on sale.

          Ironically later when I had money, I bought equipment there. I could read about it in the catalog, and buy on sale, so I did buy my first printer there, and some computers, and some stereo stuff, and my first DMM, I voujd go in kniwuping exactly what I was buying. And it was a great place to get “cutting edge” electronics for some time, it was nearby, and before bug box stores sellingbtfe same stuff. Radio Shack was niche, but more available than the hobby electronic places hidden away in a basement. So it thrived as new things came along, digital watches, computers, the mainstreaming of CB, metal detectors, pzm microphones, sampling keyboards and so on. That allowed them to profit on every corner, and keep the parts in stock.

          Michael

          1. let me share my prespective….1978…WHAT Internet…..let me…tell you about sneaking into the science building at Cal State Stanisluas and playing Othello on a DEC teletype like terminal whose output was on 17″ wide green and white striped “computer paper”…that terminal was connected to a DEC PDP8 (irrc) that ran RSTS/E and talked to a host at SLAC that was interconnected to about 40 other hosts around the US and Europe…..that Othello program?, it was written in Dartmouth Basic and was hosted on a computer at Princeton….in those days I bicycled past the only Radio Shack between Modesto and Fresno and as a tech besotted 14 year old that store was a treasure of parts and ideas…..my only other parts source was scrapping old or broken equipment but that was also a valueable resource to the local repair shop…so i had to get lucky and hope that what ever i found was light enough to carry home…..gas was 60 cents a gallon and a color TV cost at least 2 weeks wages

          2. WHAT Internet…? 1970’s had no internet. There was sneakernet, which meant walking down to Radio Shack or the mail box to order parts from Jameco or that new place called Digikey, with the 100 page catalog.

            Reading a lot of the earlier post one thing stands out. Some of you seem to think that microcontrollers with free development tools have always been around. Certainly NOT SO. Until Microchip started to give away its IDE microcontroller development kits were the sole realm of electrical engineers, and at the grace of their company. Development kits were expensive ($500+, I’ve seen kits over $3500 ), were product-specific to a family of 1-4 micros and required an entirely new toolkit ( hardware AND software ) if you switched to another micro. You all just now getting in on electronics are spoiled by the Adafruits and Sparkfuns of the era, where the difficult work has been done for you when all you have to do is plug parts into a breadboard, hook up a couple LED’s and download code. You got there on the shoulders of engineers who pioneered these tools, as they got where they were on the shoulders of the transistor generation, etc, etc, etc.

        2. I was a kid in the 70’s and radioshack was pretty good. They had plenty to keep a kid who was interested in electronics and had paper route money busy enough. They were decent up to the early 80’s. If left the states for twin overseas tours (83-89) and when I got back they seem to have started to change for the worse, though there were still bright signs (10 meter ham radios, etc) But the seemed too interesting in trying to be a Jr version of Circuit City as opposed to being a hobbyist mecca. Didn’t work out too well for them.

          1. They were really an electronics hobby store until about 1985, about the time they discontinued the TRS80 lines and started making the Tandy PC clones. They lost their sh*t over the PC movement. That was when all the radio and electronics stuff first got shoved aside, when a passer-by could be forgiven for thinking they sold nought but PC clones and perhaps R/C toys. This was kind of a prelude to the morphing into a cell phone store in the early 90s that everyone remembers

    2. I work in IT and feel the same way about the loss of the local computer shops. It’s really frustrating when you need a relatively common (or at least used to be) cable or whatnot while on-site at a customer’s location, and you have to tell them you’ll be back in two days to finish because you need to order a $5 item because there just isn’t anywhere you left you can go pick one up from.

    3. Arrow sells a lot of things with free next-day shipping. You can even order one $.25 capacitor and get it FedExed for free. I don’t know how sustainable that is, but that’s what they’re doing.

  5. There was a RS in a strip mall with a Walmart when I was a kid in the 70’s. My mom would drop me at the RS, and she’d go shopping and pick me up later. It was nice back then. The RS employees “knew their stuff”. You could ask and receive some pretty good info.
    Right before RS closed for good, I went in to get a replacement capacitor for a switching regulator that was leaking.
    Kid asked me “can I help you”. I said I needed a 1000mf electrolytic cap @ 250 volts.
    Deer in the headlights look… He pointed me to the components and I found it myself.

    1. For a long time, it was a place where people interested in electronics, be they students or hobbyists, could find part time work. Other than the employee discount, it likely wasn’t that different from other part time work, but it aligned with your interests. I knew two or three people at school who had jobs there, maybe others. Since it was their interest, they paid attention, so could be helpful. Later, it seemed like the employees were detached from what was in the store, they would have been the same way at the shoe or clothing store, but they landed at Radio Shack.

      Michael

    2. When I was a kid in the late 70s, early 80s, I was building a project from a magazine and I had an RS part number of a resistor I needed. I went to the local store and found a resistor of the same value, but not the same part number. I ask the lady behind the desk if this resistor was the same as the part number I had, and she said I had to make sure if they were regulated the same. I just thought “Wow, there is a whole aspect of resistors I know nothing about”. I wasn’t until later I realized she was talking about the power rating.

      At least where I grew up, RS employees in the olden days didn’t “know their stuff” any better than they did in the final days.

  6. I had one of the big kits, like 100-in-1. Once I got through the fun projects, liked experimenting with the radio receivers and transmitters, fundamental electronics, even some simple logic gates and a memory cell. It ate through batteries like an SOB, remember substituting the bulb with the LED to cut down power usage. Good times.

  7. Wow, this brings back memories. Yesterday I was cleaning up some of my old stuff and ran across all of my RS P-box kits. They are pretty beaten up after being bashed around in boxes for 40+ years. But their affect on me when I was 10-11 was immeasurable. The first one I built was the AM radio and it was missing the germanium diode that was used as the detector. I naively thought I could just stick in an IN914 silicon diode and it would work the same. It didn’t and the sales guy at Radio Shack pointed this out to me and explained why. He didn’t have any germanium diodes in stock but he had a junk transistor radio that we salvaged a diode from to get the thing working. I might try to clean them up and get them working again. Probably have to replace all of the electrolytic caps. All of the transistors look like self biased germanium as well. Would be a fun project.

  8. Waves of Nostalgia! I bought the P-Boxes with bags of pins back then. My Arduino Uno R3 now resides inside it as a “breakout box”. The plastic box prevents shorts to the Arduino board, and has D-Type connectors mounted in the P-Box to interface to the Amateur Radio HB Rig.

    1. I got my oldest son (who was 8 at the time) a vintage RS 200-in-1 kit. Haven’t found anything similar to that for what I want the kid to learn. (https://www.ebay.com/itm/Radio-Shack-Science-Fair-Exploring-Electronics-Lab-200-in-one-Project-28-265/192693186582?epid=2254421225&hash=item2cdd68b016:g:xcIAAOSwl3xbx8aS:rk:3:pf:0)

      As he grew older, I gave him my copies of the RS Transistor Projects books. These are getting a bit hard to find, though (https://www.ebay.com/itm/VINTAGE-1975-TRANSISTOR-PROJECTS-RADIO-SHACK-VOLUME-1-96-PAGES/372510453232?hash=item56bb5a6df0:g:CsgAAOSw68hbfvXE:rk:4:pf:0), but again well worth almost any price.

      He is 16 now, and regularly uses an Arduino Projects kit that was recommended to me by a HaD regular a couple of years ago.

  9. I used to work at a ‘shack. When mine closed (long ago) I scooped up box of random electronics parts for $20. There were two p-kits: goofy lights (cool circuit relying on neon bulbs as active elements), and a 100Khz crystal oscillator (HUGE crystal) that I beat against a SW station and continue to use as a frequency reference. I thought those p-box projects were very well done AND very inexpensive. Yes, the perf board is plastic and very easy to melt even by accident soldering the component leads.

  10. I still have a bunch of SAD1024s that I bought on clearance after they discontinued the Reverb kit. Never finished building that all the way, young me ran out of money to buy the transformer, case, and knobs to finish it. I still have my Strobe Light built from their kit.

    Loved those P-Boxes. I had fun with constantly rewiring the Goofy Light.

  11. I had the SW receiver kit shown here. The tuning coil was designed to be wound over an AA battery – quite a clever idea, given that was something everyone would have had. I still own the kit and shudder when I look at the awful solder joints. I used to enjoy using it to listen to ‘illegal’ CB in the early 80s in the UK as it would tune up to 27Mhz. And of course back in those days, the Russian Woodpecker all over the bands.

  12. I had the AM radio kit shown here when I was 10 years old. My cousin partially built it, and he gave it to me, and I finished it.
    I am an electronics / RF engineer today, and that kit was part of my education.

  13. My first was a Lionel (trains) radio with a real transistor! My older brother’s train transformer with it’s 6 to 12 volt “throttle” was my first power supply. Poly Packs was the first connection to cheap parts for me, snail mail. We had a local parts store that’s still around in it’s same location and Grahams from Indy, it’s local store was called Lafayette radio supply. Of course it often got confused with the mail order outfit of a similar name, of which it had no connection.

  14. I had a lot of the pbox kits growing up. I did one of the goofy light kits and took the idea a bit further and built one of the random ones from scratch but used lots of NE2’s and built it on a 2×4 foot piece of masonite with 2×6″ lumber surrounding it and a piece of that frazzled clear plastic they used to put in front of built in fluorescent lights on the front. It was really cool up on my wall back in the day. Makes you wonder if we all just a lot more easily amused back then?

    Decades later I got a girlfriends-sisters-kid one of the 200 in 1 kits for christmas. I got him very interested when I was there as we would take the things they had as projects and expand on them. I dunno if it ever got much use after that. I hope that it did. I would have killed for one of them at his age.

  15. In Australia, we had the Dick Smith stores and their ‘Funway into Electronics’ kits.
    There were three ‘tiers’ each with a book of all the projects in the respective tier, and you would go to the store and buy the prepacked bag of parts for the respective project you wanted to buy.

    First tier was simple circuits with springs screwed to a plastic breadboard similar to the article.
    Second tier was slightly more complex circuits like in the article but on proper PCB
    Third tier was more complex logic and TTL etc level stuff on PCB.

    I also used to mess around with the electronics, robotics and programming books published by the UK based Usborne Publishing, who recently scanned some of their books for free download. Oh the nostalgia! My favourite was the Computer Controlled Robot one. I should build it again one day with my son when he is a bit older.

    https://usborne.com/browse-books/features/computer-and-coding-books/

    Good times.

    1. I recently picked up all three books as well as a complete Funway 1 kit with another copy of the book all sealed up. I don’t know weather to keep it as a collectible or to do a YouTube series for each project.

  16. I remember my uncle who never bought gifts for anyone bought me the Goofy Lights kit. I was missing a Cap…. Went to Radio Shack and they did not have the exact component. The guy sold us 2 Caps and showed me how to wire it so it should work and why. That one light flashed a little brighter and faster than the rest. He was close. That was then.

  17. That takes me back. I did a few. Same problem as related before. I also got my boost into electronics, twiddling my way through analog stuff. I still do some of that, sorting out why certain MOSFETs behave the way they do, including the specs on the datasheets. Now I build digital stuff, in fact some of parts were bought from RS as they were being spun down. In fact the batteries I use, good old 18650s all came from those stores. Darned fools, selling those batteries and oblivious to the holders that would be needed.

  18. Anyone else build the one-tube receiver only to be stymied by finding a 22.5V battery? My Dad tried to tell me it would probably work on 24V (which, beinga ham, he just happened to have on hand), or that we could series up any combination that added to22.5, but I was 8 so it just had to be what was called for.

  19. As an 8-year-old kid, I remember begging my dad for the RS 50-in-1 kit for Christmas. The kit was $17 in an era when he could fill his Beetle’s gas tank for under $3, pricing it way beyond my reach (and darn near out of his!) He asked me a lot of questions to make sure I was going to play with it, and yes, it ended up under the tree that year.

    I built circuit after circuit with that kit, playing with it well into high school, and eventually using the parts in other projects. I can’t imagine that a $17 investment in education could have been better spent.

  20. I built the RS Micronta dual + & – power supply with their parts and PC board. It had one diabolically evil flaw: when you turned it on, the output went to maximum for a fraction of a second, so it would burn out anything sensitive that it was connected to. A 6 volt lamp would flash like a strobe light when it powered on. Pissed me of! I finally cut some traces and added some resistors and capacitors to fix the problem. It was a very badly designed circuit!

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