A Queen Mystery: The Legend Of The Deacy Amp

It sounds like a scene from a movie. A dark night in London, 1972. A young man walks alone, heading home after a long night of practicing with his band. His heavy Fender bass slung over his back, he’s weary but excited about the future. As he passes a skip (dumpster for the Americans out there), a splash of color catches his attention. Wires – not building power wires, but thinner gauge electronics connection wire. A tinkerer studying for his Electrical Engineering degree, the man had to investigate. What he found would become rock and roll history, and the seed of mystery stretching over 40 years.

The man was John Deacon, and he had recently signed on as bassist for a band named Queen. Reaching into the skip, he found the wires attached to a circuit board. The circuit looked to be an amplifier. Probably from a transistor radio or a tape player. Queen hadn’t made it big yet, so all the members were struggling to get by in London.

Deacon took the board back home and examined it closer. It looked like it would make a good practice amplifier for his guitar. He fit the amp inside an old bookshelf speaker, added a ¼ “ jack for input, and closed up the case. A volume control potentiometer dangled out the back of the case. Power came from a 9-volt battery outside the amp case. No, not a tiny transistor battery; this was a rather beefy PP-9 pack, commonly used in radios back then. The amp sounded best cranked all the way up, so eventually, even the volume control was removed. John liked the knobless simplicity – just plug in the guitar and play. No controls to fiddle with.

And just like that, The Deacy amp was born.

The Sound

Now guitarists love the term “tone”. It’s used to describe the overall sound of the guitar, amplifier, and any effects devices in between. Words like “mellow” and  “crunchy” come into play. It can be hard for a non-guitarist to keep up. John’s amp had a nice warm tone, slightly distorted – yet pleasant to the ear. He used it for awhile, then brought it along to a practice session with his Queen bandmates. Guitarist Brian May took an interest in the amp. Now Brian is a hacker in his own right. His guitar, the Red Special, was built as a father/son project when Brian was a teen. The Red Special deserves an article all its own, so keep your eyes peeled for that one. Brian often played through a treble booster. This is a single transistor circuit acting as a 30 db preamp. It guarantees any amplifier plugged in will have its input stage driven to distortion.

Plugging this setup into the Deacy amp changed its sound even more. The overdriven amp sounded different from anything they had heard before. Not quite the warm sound of an overdriven tube amplifier, but much smoother than the clipping sound that came from distorted transistor amps of the time. It also had a sustain to it. The Red Special suddenly sounded like a violin, a cello, or even the human voice. Brian loved the sound and kept experimenting with the amp.

Queen’s sound guys loved the amp as well. It was very consistent, which made it suitable for layering tracks in a recording studio. Guitars are typically recorded by connecting them to an amplifier and then pointing a microphone at the amp’s speaker cabinet. Exactly how to place the microphone and amplifier, as well as the settings of each is as much art an art as it is a science.

The dusty Deacy Amp hard at work in 1998. Image Source Glen Fryer

Brian quickly adopted the amp, and it became an integral part of Queen’s early sound. You can hear it in classics such as God Save The Queen, Killer Queen, and the more recent A Winter’s Tale. In my humble opinion, the most interesting use of the Deacy amp would be Good Company, from Queen’s album A Night At the Opera. Brian layered track after track with the Deacy. In the end, he reproduced the sound of an entire brass band, just using his guitar.

And that’s how things stayed – Brian used The Deacy in many recording sessions from the 1970’s all the way through the 90’s. It never failed or needed adjustment. In fact, the amp was never opened after John Deacon built it. That all changed in 1998, While recording “Another World” Greg Fryer asked Brian about building a replica for the now aging Deacy. May agreed, and work soon started on studying the original.

There is a certain level of stress an archaeologist must feel when peeling back layers of dirt at a dig site. Greg Fryer and Pete Malandrone must have felt the same way when first opening the Deacy. The pair had no idea what they would find inside this decades-old hack. There was a real chance they could mess this up, and a working piece of rock history.

Carefully removing the back, the two found a single circuit board. It was a four-transistor circuit. The power section was a class B amplifier in push-pull configuration. The power transistors were AC128, germanium devices. Both input and output were transformer coupled, with the power transistors mounted above the two multi-tapped transformer cores. It was a bit odd, both electronically and physically, though some parts of the circuit seem to have been taken directly from the Mullard transistor manual.

Cloning an Original

The board was definitely from a low-cost mass-produced piece of consumer electronics. Replicating the basic design would be easy. The hard part would be replicating the transformers. The two transformers were cheaply made and had multiple taps. One could measure the resistance of each tap, but short of unwinding them, it was impossible to know exactly what material the core laminations were, or exactly how many winds there were.

The pair closed the amp up and began designing the replicas. The first try had a similar sound to the Deacy, but wasn’t quite there. Greg continued to refine the design in his spare time. Each iteration getting closer to the Deacy’s sound. By 2003, replicating the amp had become a mission for Greg. He enlisted Nigel Knight to help with the effort. The hope wasn’t just to provide a few amps to Brian but to create replicas which could be purchased. There are thousands of Queen fans out trying to replicate the sound of Brian’s guitar setup. This would be as close as they could get.

In 2008, Brian gave the OK to completely tear down the amp, and determine what exactly was going on. The transistors were individually tested. The transformers were examined and tested by transformer manufacturers who came on board to help. Loops of wire were wrapped around the transformers, creating yet another secondary coil. Injecting and signals on the unknown primaries and reading the output on the known secondaries helped determine the transformer’s performance.

Many parts were found to be wildly out of spec. The AC128’s were both at the far opposite ends of what the datasheets called nominal. In a push-pull amplifier, you would want a matched pair of transistors. This pair was about as far from matched as one could get. The result was that for a sinusoid waveform input, the lower peaks of the waveform would begin clipping long before the upper peaks. This was one of the keys to the Deacy’s sound.

The result of Greg and Nigel’s work was the Knight Audio Technologies Deacy Replica. This wasn’t a cheap unit, pricing at well over 1,000 pounds sterling. It still sold well and satisfied just about everyone, including Brian May himself.

The Origin Mystery, Solved

The mystery still remained – where did the amplifier come from? Nigel postulated that it was originally part of a baby monitor or intercom of some sort, as it was a stand alone amplifier. Usually a radio or tape player would have placed all the parts on one circuit board. Both Greg and Nigel posted photos of the Deacy internals in the early 2000s. This brought the greater Internet on board. Surely the Internet would be able to find the origins of a common circuit board like this.

Unfortunately, the answer was no. The years went by, and curious searchers, including this article’s author, found nothing. That is, until January 2013. [Mitch, aka PBPP] on the antique radio forum dropped a bomb of a post. He had found the origin of the Deacy amp board. It was the amplifier section of a transistor radio after all, specifically the Supersonic PR80. He took it a step further and found documentation on the beast, in SAMS Photofact Transistor Radio Series TSM-60, published October 1965.

Supersonic was a company which built consumer electronics in Africa. They manufactured in Rhodesia and South Africa during different periods. Still, this particular model of radio is relatively rare to find. So far, only [Manuel Angelini] has come forward with photographic proof of his own PR80 amp board.

So, while the mystery of the Deacy amplifier origin story was solved, the actual components were just as hard as ever to find. Germanium transistors are becoming quite rare. Soon, the only way to get that Deacy amp yourself will be to fire up some DSP software and simulate it.

56 thoughts on “A Queen Mystery: The Legend Of The Deacy Amp

  1. Interesting story. Another point that was not mentioned (AFAICT) is that Ge transistors had leakage, that is significant collector current would often flow with no base current applied. This would actually lower the crossover distortion in class B output stage.

      1. That’s your own opinion, and you are welcome to it.
        However, I didn’t use the word “best”, I used the word “iconic”. Anyone who says that Queen isn’t one of the most iconic rock acts obviously hasn’t been paying much attention to the rock scene. Most rock and metal acts of the last 30 years list Queen among their influences. Whether you like them or not, they are iconic.

        1. Spot on. And in terms of pushing recording technology to the max, nobody can come anywhere close. And song constructions-lyrical flair and musical brilliance-simply the very best. My 12yr old son who’s into creating Electronic Music, looks up with a WOW when I play Queen songs are played. Generations will honor them.

      2. It’s ok to have an opinion Sheldon. But why do you have to only post negative stuff? Your reputation precedes you girlfriend… This is very cool and historic content that can’t be matched by power chord thumpers that you probably revel. But don’t get me wrong, I like those guys as well. Send us all a link to you playing the entire Bohemian Rhapsody track, or anything equally creative, and I’ll eat my words. Boofs like you just need to be unplugged. You probably have been.

        I recently built a relic parts-caster strat with the inline Burns Tri-sonic pickups and phase switching electronics that Brian May used on the Red Special. It’s a bitch to put together, but a revelation when you hear the tone. The effort that went into this, and the music Queen produced should not be diminished. There’s a differentiation between this axe, it’s sound, Queen’s portfolio, and everybody else. While I appreciate your opinion of Queen not landing in “YOUR” top 10, you are 99.3% crazy if you don’t appreciate the work they’ve done.

      1. In his Rock ‘n Roll days, during a recording session for Marty Robbins, a capacitor failed in the Bass Guitar amp.
        It was not discovered until they replayed the tape. Marty liked the unique distorted sound it made and kept it in the final cut.

      2. The original “Blueberry Hill” song has a section where the recording tape stretched and when played back you can hear the slowed down vocal. Most recording studios after that used acetate based recording tape because it would break rather than stretch. A break was an easy fix, a stretch was not.

  2. i built a crunch box (not a pedal because why would i want to turn it off) with an insane amount gain. sounds great even though i didnt have the correct value components. i learned how palm muting works and now i can play thrash metal.

    i never liked queen or their sound, but im the type that consider SLAYER!!! to be easy listening lounge music. but i can totally respect the art of chasing that tone you want.

    1. I guess it falls more into the arena of modding and circuit bending, but I had good luck using computer speaker amp circuits for distortion and overdrive. A couple of pots and a stomp switch and it worked so well, I ended up building a few more for fun as gifts for my buddies.

  3. Great write up and article :) Very interesting reading. I had always heard myths about the Deacy it seems. Probably the best was that it contained the heating elements of his toaster as some coil wrapping (you should have seen my face when hearing that too). My other fave that I actually heard from 3 people independently was that it had a pencil as a resistor that worked like a tube when heated with current or somesuch bs. I just assumed the speaker had some sort of small tear or failing or saturated cap but boy was I wrong. I love the ingenuity of rock n roll legends :)

  4. “fire up some DSP software and simulate it” are you kidding? when it comes to stuff like that, nothing but the real vintage parts washed in unicorn tears assembled with tools no less than 40 years old is going to sound right. Musicians can be even more silly/superstitious than audiophools

    1. “Formed in the Forge of Time by the First Gods with the concentrated creamy thigh-sweat of nude elven virgins in flowing Mithril capes riding unicorns on a rainbow under the light of a Blue Moon with the furious creation of the Universe erupting in the sky.”

      …I think it was depicted on an Asia album cover at one point, or at least a jacket.

  5. Great article.

    I’ve always been tempted to build some kind of guitar effects thing, but since I don’t play guitar it’s always been “too hard” because I can’t test it. Maybe I should just build some shitty amplifier and sell it as a distortion pedal!

    1. yeah just have a go! I once just put two “microphone pre-amp kits” of the type that teach you how to do soldering in series, and it gave a pretty nice crunchy sound.

    2. Build yourself a CBG or just snag a $20 single coil POS on goodwill to test things with :) Hopefully that will remove the hesitation to plug in and shake the walls :) I would be happy to help you get started but most folks just go for a kit and modify that. Best of luck and keep on rocking :)

  6. This is Mitch (PBPP) from the antique radio forums. I solved this mystery in less than thirty minutes time since I had indexed numerous schematics from the Sam’s Transistor Radio Series. Whoever contacted me for help, (using a fictitious name) stole the information and deleted his posts.

    This person is the lowest life form on earth. You have my permission to vaporize every molecule of flesh in his body.

    ~ Mitch ~

      1. As soon as I saw Yuri deleting his posts, I grabbed what information was left and reposted what I could. One of the moderators immediately locked the thread when we realized what was happening. You can read the entire thread here, less what was deleted by this thief.:


        I strongly suggest you do not have any dealings with this rip-off artist.

    1. :(
      Given how fast you found it, it Goes to show that knowing who to ask (or what to ask – don’t Google “measuring cup size” if you want to know he size of a US cooking cup…!) can be 9/10 of the answer.
      The middle-men like this guy who connected the question with the correct guru rarely gets noticed or credited – unless of course they do something scummy like this :(
      Some credit to him – had he not asked you, we might never have had the answer.

    2. Thanks for stopping in, Mitch! Thank you for solving this mystery. You’re absolutely right about “Yuri” being a scammer. I didn’t want to give him an ego boost by mentioning him in the article. The irony is that he brought the amp to your attention, and you solved the mystery. So he did play a role, before showing his true colors.

      1. Fabio,

        I want to personally thank you for writing this article. Like a good journalist, you did some excellent research and checked all the facts before putting pen to paper. Kudos!

        I also want to thank a fellow antique radio member, Jason, for bringing this awesome article to my attention. Otherwise, I wouldn’t have known my efforts were recognized. I’m a bit humbled to play a part in solving this and it’s cool to have a little something to be proud of.

        I’d really like to see this story hit the Associated Press. It would be a refreshing change of pace from the other junk you read in the paper or watch on TV.

        Thank you for not mentioning Yuri in the story. Even though he did it under false pretenses, without him posting the question to the correct group of people, the mystery might not have been uncovered.

        Again…thank you,

  7. Amazing that that sound came from a pile of hacked together junk, some of which had been thrown out as garbage. Even more amazing that it’s stayed working for 45 years.

    If he’d taken a different route that night, or if a yowling cat had distracted him from spotting the wires hanging out of the skip – Queen might not have come to anything.

  8. A transistorized audio amplifier–and not a good one, at that–straight out of Popular Electronics, c.1960.
    Oops; sorry, PE, this wasn’t you, for you had impeccable engineering know-how and would, at the very least, have designed proper biasing networks for the germanium transistors.

    I have a serious problem with a transistorized amplifier found in 1972 which contained germanium transistors not biased to mitigate thermal effects, the techniques for accomplishing this being very well known as early as the mid-50s
    For obvious reasons I suggest this become known as the Piltdown Amplifier.

    What’s your next try at creating an urban legend, Hackaday?

  9. Great story! I still have a SONY AM radio from the late 60s that I got as a kid. In my teen years I figured out how to tap into the volume control to use it as an amp for stuff, including guitar. The sound was distorted yet creamy… very unique. Great things happened when playing fourths and fifths. I also believe the magic came from – transformer overload nonlinearities, the speaker, and the germanium characteristics. Raid your grandparents’ basement for any 60’s era portable radios or tape players; they’re likely to have similar amplifiers.

    If you still want to play with germanium transistors, there’s still quite a bit of new-old Soviet germanium devices on the ‘bay.

  10. I am also a denizen of Antique Radio Forum (where the information about the origin – which, by the way, was unequivocally correct and amazing detective work from Mitch). I have to say, what happened in this case is an egregious case of taking advantage of someone, one of the worst I have ever seen ing 20+ years of hobby forum behavior, back to the Compuserve era. Mitch/PBPP was trying to be helpful and someone, essentially under false pretenses, abused Mitch’s helpful nature. The guy behind this is persona non grata and scum.

    BTW, I can confirm Mitch’s account of the affair to the letter, I saw the entire thing play out at the time. The output board was beyond a doubt exactly the same down to the product number from the TSM Mitch posted.

  11. I wanted it to end with them finding out the original was a replica bought by a timelord to use in a Dalek-stopping machine, & subsequently dumped in the skip. Why else would the transisters be that way? The doctor adjusted them, & because of the time feedback loop, they were perfectly adjusted for to stop the Daleks!

  12. Of course by the time HaD got around to publishing this article, the Deacy replicas were all sold out, despite the site saying the last 50, they, nor anyone else, has any for sale – except one listed very recently as used, at almost double the original $1,300. How many of these were made?

    The most ridiculous part of the replication process was having to laser blast off the old lead solder from the transistor legs for RoHS compliance. As though the sub milligram amount of lead on 12 transistor leads, sealed inside a $1,300 device that nobody is ever going to open up let alone throw away, would ever be a threat to anyone. But hey, government is rarely known for exhibitions of common sense.

  13. I’m a little surprised that no one has suggested reducing the negative feedback loop. Doing so would increase the natural distortion. Neg fb is more important in normal amplifiers than in instrument amps.

    Also, props for the use of the transformer phase splitter. I built a small tube guitar amp with one years ago, it had great sound, got talked into selling it. Wish I had it back. That approach is underrated.

  14. A late update to the Deacy amp story – as Adam suggested at the end of his excellent article, a software emulation might be the best choice and IK Multimedia, after working with Brian and his gear tech, have introduced an AmpliTube collection of Brian’s rigs. It includes a Deacy amp and even a battery voltage control because Brian explained to them that on some of his tracks he prefers the more crunchy sound he gets when the battery is running low! Brian, in addition to being a really fine fellow according to those who have met him, is also very picky and ran the IKM engineers through a number of iterations while developing simulations of his gear. And he approves of all the emulations including the Deacy amp model, so if anyone wants to play with such an iconic cab, there is now a good software solution approved by the man himself.

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