For anyone interested in going the modern Fairchild route, I’d check out the latest magic death eye compressors. Ian has spent the last 3 years tweaking the design to make it work with 12AU7 tubes to make it way more easy and affordable to maintain.
magicdeatheye.com/“New design Magic Death Eye Stereo Compressor
With the cost of 6386 tubes skyrocketing because of only one company (JJ) making them, and other difficult manufacturing hurdles, I spent 3 years redesigning my compressors.
The new models use the very abundant and still manufactured 12AU7 dual triode. This is not a remote cutoff (vari-mu) tube. It does have the widest bias range of all the common 12A(X)7 type tubes.
The 12AU7 can still deliver 5mA of current at -20 volts bias at 350v plate. A 12AX7 shuts off at -3 Volts.
All this means is that the 12AU7 can be slowly turns off over a wider control voltage range, closer to how a vari-mu tube like the 6386 or 6BC8 works.
So I set out to match the performance of my old design with a new design. I rewound transformers, introduced discrete op amps, amassed piles of prototypes and after 3 years, finished a design I’m proud of.
Both the stereo and mono use four 12AU7’s per channel flanked by an input and output transformer.
The stereo has a new EQ loosely based off the Sontec, using a discrete op amp (Jensen 918 circuit) with the filter circuit in the feedback loop.
There is 6dB of cut and boost for both high and low bands. Each band has 2 frequencies. There is also a 20Hz 24db/octave low cut filter.
I made sure the unit is very serviceable and robust in design.“