Fender's Harmonic Vibrato is my latest Covid-19 interest. It was included in Fender's high-tier brown face amps (I think).
Did Alembic ever reproduce the circuit in any of it's preamps?

No vibrato in any Alembic preamp ever.

I think Jorma mentioned his preference for those Fender Vibrato amps in a recent Fur Peace Ranch Online performance.

I have had some playing time with a 1961 Fender Concert amp with that circuit. It had a unique tone. The vibrato is way cool, a little darker sounding the the average later vibrato, sorta wet and bubbly at faster settings..

I've had tremolo on my first real amp, a Heathkit TA-16 that I built when I was 13, and later had vibrato on a Blackface Pro Reverb.   Other than putting a mic through the Heathkit and singing "Crimson & Clover", I never used it.

Bill, tgo

If you want a killer one, get a vintage Ampeg Gemini amp. That is the amp that they pushed the vocals through for the original song Crimson and Clover.

Funny you should mention that.  I used to play through an Ampeg Gemini in the late '70s.   It was a friend's who wasn't using it and lent it to me for a year or two.  Nice amp.  And I never used the vibrato on it either.
I'll have to ask my friend if he still has it.  (The guy never throws out anything.  He hasn't allowed anyone else in his house for the last twenty years!)

Bill, tgo

One of my biggest regrets is selling the cream colored Fender Tremolux and early 60s Blackface Vibrolux Reverb amps I owned. They were both great amps, the Tremolux cabinet had Altec Lansing 12" speakers in it, one channel was thick and dirty sounding and the other totally clean. At the time (1985/6) you could find the same amps cheap everywhere, the whole collecting thing had not taken hold yet and I thought that I could always get another 60s Fender amp cheap if I wanted one. Little did I know what was coming...

I used to have a brown Fender Pro, and that vibrato is amazing. Total Univibe feel. Overall, that amp was harsh to my ear so off it went. Now I've been home playing with my new to me Showman!