Price Paid:  $0.00 from Swapped for Stax DA-

Summary:
These wonderful amps are driving my Magnepan 3.6R with ease up to real live sound levels and believe me, the Maggies are real power hogs. When I bought the Maggies from the original owner I brought my 549s for listening test and they shamed the expensive Mark Levinson stuff that guy used.
I had them rebuilt by a specialist with the help of Tim de Paravicini as there exist no schematics any more. We used even better parts throughout and increased the power caps by 60 percent. I also replaced the original driver tubes with NOS RCA triple mica black plates and Telefunkens with amazing results.
Everything the other review says about the 509s the 549s have in spades, they are built symetrically and twice as powerful, 200W/channel and were originally designed to drive the master cutting lathes in recording studios, apparently The Exchange in London still uses them. These are my last amps, period.
Even when I drive them until their clipping indicators blink continuously the sound stays absolutely clean, perhaps it gets a tad warmer and only then they exhibit a bit of that "warm tube sound" otherwise they are absolutely neutral with much more natural timbre and transparency than even my Stax DA-100M monos (100W Class A/ch.), those were the best sounding transistors I ever heard.
Their bass is in a league of its own. I always thought tubes couldn't produce deep bass which is also taut and fast. This has kept me from using tubes until 5 years back.
If you can find them buy them! You'll never look back.

Strengths:
Best allround amps I know. Can drive even very demanding speakers like the big Maggies to more than adequate listening levels. Fast and deep bass. Transparency, detail and "rightness" with all music. Subjectively much more powerful than the nominal 200W. PL 519 Power tubes are still available cheap.

Weaknesses:
Very rare. Bias adjustment with built-in LEDs is inaccurate and has to be done by hand after opening the case.

Similar Products Used:
Sansui AU-919
AVM M1, AVM M3S monos
Stax DA-100M monos
Klimo Linnet tube monos
DIY tube monos with EL34