Brian May Deacy Amp Replica

Little known outside the Queen and Brian May enthusiast community, Queen bass player John Deacon built a small battery-powered amplifier around 1972 from a bookshelf hi-fi speaker cabinet containing an ELAC 6RM/202 speaker, an ELAC TW4/17 tweeter and part of a vintage transistor radio (either a Supersonic PR-80, Kolster Brandes International KR016 or RGD International RR214 model) which he found in a dumpster in London. It is ironic that with the myriad choices of expensive guitars and amplifiers available to professional musicians, the multilayered guitar sections on some Queen songs including The Millionaire Waltz were recorded using two home made pieces of musical equipment: Brian May’s Red Special guitar and what became known as the [legendary] Deacy amplifier.

Knight Audio Technologies (KAT) hand built around 165 authorised replicas of this amplifier from around 2011 to 2019 with production being ultimately limited by dwindling supplies of vintage germanium transistors with the correct Hfe gain values required to replicate the exact characteristics of the original printed circuit board.

I was fortunate to find unit with serial #0065 offered for sale in as new condition complete with its original packing carton and optional DABS PP9 battery simulator unit on U.K. eBay in February 2013. I was the only bidder and won the amp at the seller’s starting price – a genuine bargain. Displaying his synonymous generosity and professionalism, Nigel Knight followed up via e-mail to register me as an owner and offer me the balance of the manufacturer’s warranty.

Although there are other options to create tones with the recognisable Deacy ‘honk’ at 600-650 Hz, I appreciate and cherish my KAT Deacy replica, not least because of its relative rarity but also the massive intellectual R&D effort from initial work by Greg Fryer and then by Nigel Knight with expert assistance from Ian White of Celestion and others which was required to realise a production-ready unit.

I find the KAT Deacy sounds best when driven by treble boosters with lower gain germanium transistors such as the VPW replica Dallas Rangemaster pictured in the gallery above. When powered by a PP9 battery, the amplifier is isolated from the 50 or 60 Hz mains supply and is therefore versatile enough to be used remotely. The Brian May Deacy Amp Replica comes with a 38 page, A5 size booklet with foreword written by Brian May. Nigel Knight has made a PDF version available on his website: but the file is corrupt. However, you can download his original file and my scanned version from the links below:

Please check out some professional and amateur videos below and listen out for those distinctive parts recorded with the Deacy amp on a Night At The Opera and A Day At The Races which led Steve Vai to describe Brian May as “the most brilliant and innovative guitar orchestrator that has ever been sent forth from the Universe.”

“Brian May is the most brilliant and innovative guitar orchestrator that has ever been sent forth from the Universe”

Steve Vai, brilliant and innovative guitarist
KAT Deacy Review by Jamie Humphries for Guitar Interactive Magazine
Brian May Deacy Amp Replica Video Demo Guitarist Magazine
Brian May Red Special Enthuiast Meet 2018: Martin Pitcher & Julian Hemingway Demonstration
Brian May Red Special Enthusiast Meet 2019: Deacy Style Amplifiers Comparison Part 1
Brian May Red Special Enthusiast Meet 2019: Deacy Style Amplifiers Comparison Part 2

Technical Specifications

Amplifier Section
Form: Four transistor, transformer coupled push-pull amplifier
Output Pair Operating Class: B with asymmetric gains
Output Power (Undistorted): 750 mW RMS
Power Requirements: 9 V DC
Reverse Polarity Protection: Yes
Current Consumption (Quiescent): 12 mA
Current Consumption (Full Power): 168 mA
Transistors: 1 x AC125, 1 x AC126, 2 x AC128

Speaker Section
Form: Twin driver/passive crossover
Loading: Infinite baffle, sealed box
LF/MF Unit: 30 W Celestion 6″ twin cone 25 mm voice voil
HF Unit: 15 W Celestion 3″ Paper cone 15 mm voice coil
Crossover Device: Non-polarised capacitor
Crossover Frequency: 5 kHz

Cabinet Section
Construction: Sealed chipboard box with mitered corner joints
Finish: Sapele veneer
Cabinet Walls: Matched A/B veneered chipboard
Front Baffle: Material 12mm bare chipboard
Rear Baffle: Material 12mm bare chipboard
Joints: Biscuit-jointed mitres
Baffle mountings: 12 x 12 mm battens
Internal HF Damping: 25 mm acoustic wadding

Battery input: Flying lead with integral PP9 clip assembly. Internal strain relief.
Guitar input: Switchcraft 2 pole jack

Further Reading

Greg Fryer has published a full web page dedicated to the history of the development of the Deacy Amp replica and his involvement with it. It contains many interesting photographs and sections detailing the origin of the circuit board, his notes on his telephone discussion with John Deacon, information from French enthusiast Manuel Angelini of DoxyWorld who was the first person to track down an original Supersonic PR-80 radio from Zimbabwe (formerly Rhodesia) and the section which Greg wrote for the booklet included with the KAT Deacy replicas:

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