Part of Zappa's rack gear, as mentioned in this interview for the May-June 1979 issue of Guitar Player (as transcribed on Zappa Wiki Jawapa). It was restored by Charlie Bolois of Telefunken in cooperation with Dweezil Zappa, as specified in this July 2007 Telefunken article.

Guitar Player, May-June 1979, “Shut Up And Play Your Guitar”

What's in the large console you use on stage? It looks very complex.

Well, actually it's not all that complex. It's a little rough to maintain. Things can get broken where it's shipped around. It's got a pair of Dynaflangers, a pair of MXR Flangers. It's got one input and four outputs – two dirty outputs and two clean outputs, all stereo. There's also two Big Muffs, Systec Harmonic Energizer – all these things are in pairs – Oberheim ECF, Eventide Harmonizer, MXR DBL, Mutron, DBX 162 compressors, Gain Brains, Kepexes, a Theremin and a Biphase. That's about it, and there's about 24 switches on the floor. I add to it every year. The Dynaflangers are on the newest thing. Oh yes, there's a Mutron Octivider and a DBX Boom Box.

Telefunken, July 2007, “Telefunken USA Completes Restoration of Zappa Microphone Collection”

After the restoration of the microphone collection, Dweezil unearthed various family treasures, including the rare Systec Harmonic Energizer guitar pedal. The pedal, like so many of Frank’s other guitar stomp boxes,” Bolois explained, “was originally customized by installing the basic unit onto a circuit card and creating a module that could be plugged into a ‘lunch-box’ style stage box chassis. This kept the pedals off of the floor, out of harm’s way and closer to the amp, allowing a quieter and more reliable system. One power supply fed all of the effects units to eliminate battery worries and to insure reliability. The effects modules plugged into the main chassis and received power and I/O signals via an edge connector buss system. Of course, there was no documentation and no main chassis or power supply available for reference. A custom chassis was fabricated with a suitable external power supply.” Bolois restored the unit to working order and Dweezil identified it as one used by Frank in the 1970s “Roxy and Elsewhere” album period. He has incorporated it in his current “Zappa Plays Zappa” concert tour.

“There is just nothing like it, and it’s definitely a treat to have this for our performances of Frank’s music,” Dweezil remarked.” It is hoped that Telefunken | USA will be able to reverse engineer and recreate the unit, as they have done with numerous vintage microphones of the past.

Mentioned by former Systech president Greg Hochman in Analog Man's Guide To Vintage Effects, as transcribed by Joe Gore in this December 12, 2012 tonefiend.com article.

We did a custom preamp for a guitar that Greg Lake had. We were in Kalamazoo, where Gibson was….Ritchie Walborn had designed it; others asked us to build one for them. It eventually became what we called the Harmonic Energizer. It was a variable-state filter, which was kind of high-tech at the time, and it got a pretty good following from Joe Walsh to Jan Hammer….It allowed you to dial in up the Q of the filter, and by changing the frequency of the filter, you actually had the ability to choose what key you were going to have sustain and feed back. The thing actually had 55dB of gain when you got it up to a high-Q filter, so it didn’t allow you to be subtle onstage. It was dangerous, but it had a unique sound to it.

He had this with him in the studio during the recording sessions of Pork Soda.

In an interview with Premier Guitar, Steven Drozd discusses his collection of guitar pedals, including the Systech Harmonic Energizer.

Mentioned by former Systech president Greg Hochman in Analog Man's Guide To Vintage Effects, as transcribed by Joe Gore in this December 12, 2012 tonefiend.com article.

We did a custom preamp for a guitar that Greg Lake had. We were in Kalamazoo, where Gibson was….Ritchie Walborn had designed it; others asked us to build one for them. It eventually became what we called the Harmonic Energizer. It was a variable-state filter, which was kind of high-tech at the time, and it got a pretty good following from Joe Walsh to Jan Hammer….It allowed you to dial in up the Q of the filter, and by changing the frequency of the filter, you actually had the ability to choose what key you were going to have sustain and feed back. The thing actually had 55dB of gain when you got it up to a high-Q filter, so it didn’t allow you to be subtle onstage. It was dangerous, but it had a unique sound to it.

According to an article by Joe Gore on tonefiend.com, the Systech Harmonic Energizer was used on his guitar tracks for Tom Waits's "All Stripped Down" and on "Jets" by Action Plus.