Which high power SET

For me, #1 priority is amp's ability to drive speaker sufficiently. If not, SQ will suffer whether low or high listening levels from my experience.

Could not agree more.

Atmasphere,

Small signal bandwidth is 7Hz - 66kHz, -3dB; the OPT is of course the limiting factor and those are the actual test results provided by Monolith Magnetics. When I checked the amp with a .05V signal using TrueRTA on my laptop, which only measures from 10Hz -20kHz, it was less than 3dB down at 10Hz, and still pretty much flat at 20kHz. At full power, saturation occurs at 32Hz; I can honestly say that I don't notice any frequency limitations soundwise even at very loud volumes. I had an old friend visiting for the past weekend and we listened into the wee hours to everything from Sonny Rollins to Black Sabbath, and it all sounded great...when we cranked up Yello the walls and floor were shaking from the subsonics.

That is quite impressive to get that sort of bandwidth out of an SET of that sort of power! Do you know the configuration- by any chance is it a parafeed circuit?

06-30-14: Atmasphere
That is quite impressive to get that sort of bandwidth out of an SET of that sort of power! Do you know the configuration- by any chance is it a parafeed circuit?

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I designed and built it, so I'm very familiar with the configuration. It's a series feed two-stage direct-coupled single-ended design; no parafeed. The driver tube (the excellent Russian 6E5P tetrode, triode strapped) has an active gyrator/mu follower load to supply the grid current demanded when the amp goes into A2.

You can see the LTSpice schematic in the first post of this thread:

The Midlife Crisis

I simulated both parafeed and series feed as I was brainstorming this build; both have their advantages and disadvantages as you well know, but I decided to go for broke and make it series feed, which required me to get very expensive custom gapped transformers from Monolith (these are now part of their Summit line). I could have used a less expensive, smaller transformer with parafeed but then I'd need a custom plate choke to handle the voltage (which could swing to nearly 5000V!) and a high-voltage capacitor as well so it ends up not being much of a cost or weight advantage for parafeed. I opted for the simplicity of series feed.

As I said, the OPT is massive to be able to handle such high power; here's a picture of the wound core before strapping and potting, with an ECC83 tube for reference:

Core

Each monoblock weighs about 180lbs, and is built on a Landfall Systems aluminum chassis.

By the way, the actual schematic of the build differs slightly from the one in the first post of that thread (evolution!). The actual amp uses the AOT2N60 instead of the original AOT1N60 for better power dissipation, there are gate to source protection diodes around the 2N60, the resistor to the gate voltage supply is slightly larger, and there is a 6000V gas discharge tube across the OPT primary to protect it in case of overvoltage.