Wilson Sabrina X ... oh my God! and Jadis... or?

@daveyf: Did you mean to say "MF" (which to me means Musical Fidelity), or rather "MR" (for Music Reference)? If MR, do you remember which model? The RM-9 is pure tube, the RM-200 a hybrid (solid state input stage, tube output). The RM-9 is a classic unbalanced tube amp, the RM-200 balanced, with only XLR input jacks. Both are push-pull designs, though Roger also made single ended tube amps, which at the end of his life he was quite enthusiastic about. He also offered his own version of an OTL amp.

Modjeski thought highly of the Acoustat ESL panels themselves (I recently learned that Roger Sanders was involved in their design), but not their transformers. He actually deigned a replacement for them, and iirc even a tube version to replace the stock ss one.

Roger’s death was a great loss to hi-fi, but his talks at the annual Burning Amp Festival in San Francisco are available for viewing on YouTube.

Here’s his 2015 talk, misspelled name and all:

The first viewer comment below the video is well worth reading.

Brooks Berdan Ltd. sold Jadis when Brooks was still living, as well as Wilson speakers. But he also sold Music Reference electronics, which he held in very high regard. Brooks had some customers who bought with their eyes, others with their ears. He carried Music Reference for the latter group. Sure, he would happily sell you a Jadis if you wanted one, but he recommended Music Reference to his friends (one of which I was proud to be. His wife Sheila hired my band to play at his 50th birthday party).

The thing about mating a Wilson with a Jadis is:

1- Jadis amps (in fact most tube amps in general) don’t "like" low impedance loads. Tube amps produce their highest distortion at low frequencies.

2- Wilson speakers present amplifiers with a very low impedance load, especially at some frequencies.

3- Perhaps worst of all, Jadis amps have a pretty high output impedance (low damping factor), which makes the frequency response of the amp react to the varying impedance of the speaker load. The Result? The amp changes the sound of the speaker in terms of frequency response. John Atkinson’s Stereophile test bench results on this issue are included in all his amplifier reports.

The above is why---contrary to the common wisdom that an OTL amp is the best for use with the original QUAD ESL, the exact opposite is true. The QUAD has one of the most wildly-varying modulus-of-impedance curves in the history of hi-fi (from below 2 ohms to over 100, depending on frequency!). Used with a high output impedance amp like all OTL’s, the frequency response of the QUAD is drastically effected. Not good, obviously. I originally used a Bedini 25/25 (solid state) with my QUADS, a classic combination.

Roger Modjeski was a big fan of the QUAD ESL, and used that classic speaker in the development process of designing his RM-10 amplifier, which is THE amp for driving the QUAD. I replaced my pair of OTL’s with an RM-10 Mk.2, and learned first hand that Roger was correct and the common wisdom was not.

But the 35w/ch RM-10 is certainly not appropriate for a Wilson loudspeaker. Roger had already designed and marketed a classic 100w/ch tube amp using EL34 tubes (four per channel)---the RM-9, still in use in many fine systems. But he knew there was a need for a tube amp designed to be a better match for low impedance speakers.

His answer was the RM-200. You can read the review by Michael Fremer of both the original version and the revised Mk.2 in Stereophile. Fremer declared the RM-200 to be his choice for the best "reasonably-priced" tube amp available, keeping it in his reference system and giving it an A grade in the mag’s recommended components list, where it remained for twenty years. Twenty years!

But Roger didn’t stop there. He was (RIP) a tube expert, and came up with a way of using just a single pair of KT-88’s and/or 6550’s to produce 100 watts. EVERYONE else uses a quartet of those tubes to produce 100 watts. So what, he runs the tubes hard to produce more power (a common tactic)? No, with clever design. The pair of output tubes (in each channel) last between 5,000 and 10,000 hours!

Atkinson’s tests revealed that the RM-200 produces more power at 4 ohms that at 8---unique amongst tube amps, and that it has an unusually low output impedance (for a tube amp). These two facts make the RM-200 an excellent choice for use with Wilson’s. No, the amp doesn’t carry the cache of a Jadis, but you can’t hear cache.

Roger left Music Reference in the hands of a trusted and knowledgeable associate, who continues to provide product support. If I just had to have a Wilson speaker (or one like it), and wanted to run a pair with a tube power amp, my first choice would be a Music Reference RM-200 Mk.2. They occasionally appear used for around $3,000, a true bargain.