Loudspeaker designer/manufacturer John DeVore shows reviewer Ken Micallef his system.

Here is a video of Modjeski’s seminar at the 2015 Burning Amp get together in the Bay Area. It’s an hour and a half in length, and contains a lot of Roger’s thoughts on tube amplifier design. Some humour too.

https://youtu.be/io_yZENYlxY?si=fm15uYzIkfnWjVro&t=1

And here’s his shorter talk (just under an hour) at Burning Amp in 2018. This one is more about tubes themselves. Stereophile reviewer Herb Reichert---who himself has some experience at designing and building tube amps---is in the audience.

https://youtu.be/1pU3jNquDUo?si=oxppxXCRj8Hddysg&t=1

@clio09: Van Alstine used GE 5751 tubes (in place of the stock 12AX7's) in his modified Dynaco PAS pre-amp. Better than the ARC SP-3! 

And thank YOU @clio09, for both your post and keeping the Music Reference name and products alive.

Though reviews of tube amps in professional hi-fi mags commonly contain little exploration and explanation of amplifier circuit design, reading Modjeski’s writings on the subject (as well as other subjects ) is a free means of gaining a knowledge of what to look for in an amplifier. After Roger moved from Santa Barbara to the San Francisco Bay area, he offered a class in tube amp design at a local adult education facility. Students were not only taught electrical engineering, but also assigned the task of designing and building an amplifier of their own.

Positive reviews of tube amps that produce poor performance numbers raise a number of questions, questions to which Modjeski was willing and able to provide answers (in his AudioCircle Forum and at seminars he gave). Audiophiles tend to view the sound an amplifier produces---and the sound of the tubes in amps---being partially determined by factors other than good electrical engineering basics. Parts quality is one such factor.

While high end consumers look for boutique parts in their products, Modjeski was concerned first and foremost about parts ratings. He was an advocate of using a part with a voltage rating 10 times what that part would see in a circuit. I learned the wisdom of that approach when I turned on my factory-fresh ARC SP-3 the first time. I heart a "Pop!", then smelled smoke. I took it into my dealer, who found a resistor had blown when faced with the turn-on voltage rush. That resistor was of a voltage rating of only twice what the circuit called for. Roger didn’t make those kinds of mistakes.

Not to pick on ARC, but when the SP-3 was replaced with the SP-3a, Frank Van Alstine discovered that what was new and improved in the "a" version" were not the boutique parts claimed for it, but corrections in it’s circuit design, including the inaccurate RIAA response curve that Frank was already offering a correction for in his SP-3 modification. No "magic" parts required, just excellent electrical engineering.

That’s what Roger Modjeski was all about. It’s great to learn that @clio09 will soon be offering Music Reference products; for those who can’t wait, know that Roger "approved" of the tube electronics designed and built by Mike Sanders (Quicksilver) and Tim DeParavicini (EAR-Yoshino).

@tomic601: Right you are, pal o' mine!

@jasonbourne71: While doubting a pair of EL84’s can produce 35 watts, you failed to question a pair of KT88’s producing 125 watts. And yet Modjeski did just that in his RM-200 amplifier. For proof, read the test bench results John Atkinson got in Michael Fremer’s Stereophile review of the amp, in both original (100 watt rating) and Mk.2 (125 watt) iterations.

Few hi-fi tube amp designers have/had the depth of knowledge about vacuum tubes that Roger Modjeski did. Luckily a lot of his wisdom on the subject survives in the pages of AudioCircle (in the dormant Music Reference Forum). He designed his first amplifier (a single-ended triode) as age 6! He started repairing hi-fi electronics at a retail store while still in high school, and studied tubes for the rest of his life, visiting many tube manufacturing plants in England, Europe, and Eastern Block countries..

He then went to work for Harold Beveridge, the ESL loudspeaker designer/manufacturer. When that endeavor ended he started RAM Labs, RAM Tube Works, and finally Music Reference. His final product was a direct-drive ESL loudspeaker (no input transformer), the ESL stators and diaghrams driven directly by an OTL amplifier. WOW!

That’s the common wisdom @jasonbourne71, but one of Modjeski’s goals in designing the RM-10 was to prove that it is not a fact but rather a fallacy. Modjeski and David Manley got into a heated debate in the pages of Stereophile on this very subject back in the 1980’s, I believe it was. Manley took the RCA tube manual literally, Roger unable to convince him that the manual was merely an application guide, not a tutorial on every tube's ultimate output potential.

If you read the technical reviews of the RM-10 by numerous publications, you will learn that the RM-10 does indeed produce 35 watts from a single pair of EL84’s per channel, and doing so with the amp operating in Class A for a portion of it’s output. That’s one reason DeVore chose it as his push/pull medium-power tube amp. Roger later made a special version of the RM-10 that was rated at 25 watts per channel pure Class A, again from a single pair of EL84s per channel.

By the way QUAD ESL owners, the RM-10 is a great amp for use with your loudspeakers. Unlike OTLs, the RM-10 has a low (for a tube amp) output impedance, so doesn’t interact with the insane impedance swings of the ESL the way OTLs do.

@toro3: Hey, John has the same cassette deck as me, the Nakamichi BX300. Thanks for the link. It’s interesting; he has a lot more gear and LPs in the listening room at the DeVore factory that at his home. I’ll bet he spends more time at the former than the latter.

The turntable, arms, and phono cartridge collection at the factory are incredible! His wall of LP’s there looks like mine, but our musical tastes are miles apart. I’m sure John also has a wide variety of music in his collection, to also use in his loudspeaker design process.