If you have read erik_squires misinformation, please understand that he does not even know what a MOV looks like. https://forum.audiogon.com/discussions/what-shunyata-and-furman-smp-have-in-common-inductance
Erik is merely trying to hawk his affiliate links for profit. If you are interested in the Furman PST-8 that he promotes, this is the only link to use AFTER clearing your internet browser of cookies:https://www.amazon.com/Furman-Aluminum-8-Outlet-Protection-Conditioning/dp/B000YYVLAK
Here is a summary of the relevant information:
Furman does not license series mode surge technology. They were sued by Zero Surge - the originators and license owner of the series mode technology patent - and lost. Furman was forced to call their technology SMP (Series Multi-Stage Protection), which still uses MOVs. https://www.furmanpower.com/furman-technologies/series-multi-stage-protection
SurgeX, Brick Wall, and Torus Power are the only licensees of series mode technology that I'm aware of. McIntosh - with the MPC1500 - appears to use series mode surge technology as a repackaged Torus. "Torus Power Technology under license from Plitron Manufacturing Inc."https://www.mcintoshlabs.com/-/media/Files/mcintoshlabs/DocumentMaster/us/mpc1500om05L.ashx
"Zero Surge® was incorporated in March 1989 by J. Rudy Harford." He is the founder, and was the former owner and president. And yes, he’s the license owner.https://zerosurge.com/about-us/
Look at the SMP circuit linked below. There are clearly MOVs. The same circuit board is used in all Furman products with SMP. https://www.furmanpower.com/sites/furmanpower.com/files/_/Power-Report/smp-circuit.jpg
Still don’t believe me? "Furman’s Series Multi-Stage Protection Plus (SMP+) addresses some of the shortcomings of traditional MOV-based protectors by employing a variety of circuits to clamp, absorb, and dissipate transient voltages without having the device sacrifice itself. The company claims that MOVs used in a properly designed circuit will not fail.
Furman’s SMP+ circuitry takes pages from both shunt-and series- mode playbooks and adds its own twist. Along with a high-voltage MOV and a high-amperage thermo-fuse varistor, SMP+ uses a tuned circuit that includes series inductors, a bridge rectifier (which con- verts AC to DC power), and high-voltage capacitors."https://zerosurge.com/wp-content/uploads/2016/10/Sound_and_Vision_July2007_Zero_Surge.pdf
"SMP allows Furman products to offer this protection without damaging any of their own internal components—that is, they are virtually non-sacrificial" Virtually, meaning not quite.https://www.mixonline.com/technology/furman-sound-implement-smp-technology-381312
"• Zero Surge’s patented filter technology protects sensitive electronics from even worst case surges, repeatedly, without degradation or failure. MOV-free."https://zerosurge.com/wp-content/uploads/2017/09/zero-surge-brochure.pdf
" • No sacrificial or wear components (no MOV’s)"https://www.brickwall.com/pages/the-worlds-best-surge-protectors
The series mode surge technology patent states, "Provides an inductor system as the first means of protection."
"A branch circuit SPD (Surge Protection Device) using an MOV in front of, in back of or sideways of, a small ferrite core series inductor, labeled as ’series something’, is in my opinion, a marketing persuasion by our competitors intended to ride on our back and confuse you, and the only way to promote a product ’looking like ours’ without violating our patents. Are you a Switch or a Filter?
An MOV is a semiconductor switch. Switches will wear out and can suddenly fail when stressed. The monitoring of these switching devices over time as ’functional’ is tedious and a guessing game at best. A filter properly designed for its application will not wear out and will only fail if misapplied. Think about your passive LC subwoofer crossovers...when will it wear out?...perhaps when you wire it up to 440V just for fun?...or when you listen to too much music?" Michael McCook, SurgeX International
Furman purposely added MOVs to create a hybrid surge protection device that does not violate the patent. Due to the patent, Furman can not call the design series mode technology, and renamed it SMP+ in 2005. The whole point of series mode technology and the reason it was created is to avoid the use of MOVs. It’s fully ironic to use MOVs and call it series mode. It would be akin to saying you’re dying of thirst, and then eating the saltiest food you can, or calling a fat guy slim.
SurgeX does not have the same basic technology as other series mode designs. They have added ASM (Advanced Series Mode) technology. This adds an extra winding to the air-core inductor to further improve the surge protection and lower the let-through voltage.https://www.ametekesp.com/-/media/ametekesp/downloads/white-papers/surgex-ametek_white-paper_advance...