Cliff Brown founded 633 Engineering to pursue a long-term obsession with producing the ultimate in electric guitar amplification.

His amplifiers represent the culmination of more than 30 years experience working in Pro-Audio, designing, building, servicing and customising backline and professional audio electronics and over 35 years of playing electric guitar.

He wanted to create an amplifier that would allow each guitar's unique voice to be heard without masking its tone in any way. He wanted an amp that could have its sweet spot at any volume level and that would allow him to use the guitar's volume and tone controls to maximum effect. It had to be reliable and give consistent tone night after night.


It also had to be a thing of beauty.
633 amplifiers are designed and built to the highest no-compromise standards. Classic designs have been refined and new features added to give the player another level of tonal response, touch sensitivity, versatility and reliability. 

Using the very best components they are built to last a lifetime. The designs have been tested and refined over many years and have proved themselves time after time on the stage and in the studio.
Cliff Brown

“Best amp I’ve ever heard or played”
— Stuart Dixon, guitarist, producer, engineer


The Custom 44 is a fully featured amp based on the Safire. This example and its matching 2 x 12 cab were specified in Teal Blue with a stunning oiled ash front to the head.

Based on the 36-watt Safire, the '44' has a beefier solid state rectified power supply that gives a little more headroom and punch at the low end. A change in the voicing on the preamp extends the lows a little.  


The bias-modulating tremolo comes with a foot switch-able speed control so the player can switch between fast and slow modulation.  The change in speed is not instant but takes a few seconds - just like a Leslie speaker.




This amp also features the foot switch-able More control adding more preamp gain and switching in a master volume control that has both attenuation and gain.  This simple control opens up so many tonal possibilities adding refinement to traditional "rhythm/lead" switching, maintaining the character of the single channel amp but with the required increase in gain, compression and volume.




The More function is linked in with the studio quality reverb, allowing the size and level of the reverb to be changed when switching adding another level of sophistication.

It puts out 44 watts through a pair of 6L6s and has a variable headroom control that allows the sweet spot to be found at any volume.


Three control preamp with Volume and High and Low tone controls
Three-position Voice switch:
Bass light - keeps things really tight when the amp is pushed hard
Mid focus - great for fattening up single coils
Deep - big round cleans with vintage style break-up when pushed hard


Unique 'More' control
Bias modulating Tremolo with foot switchable speed
Lush studio quality reverb with four-way interaction 
Variable output headroom


Transformer balanced Cabinet Simulator Output
44 watts from 4 x 12AX7, 2 x 6L6
515mm x 211mm x 214mm, 15kg
All hand built in the UK












Guitarist Magazine gave the Groove King a whopping 9/10 and a 

Choice Award and the Custom 36 a staggering 10/10 and a Gold Choice Award. 

To find out why check out the comprehensive review in the August 2016 edition or online at Music Radar:-

Groove King Review