Packing Up The Lab


Life happens, as they say. We’re getting ready to move, so I’m packing up the lab today. I’ll probably be out of commission for awhile. Still reading email and glad to help if you have questions, though I may be a little slower than usual to respond. Hopefully, later this Fall I’ll have a workbench again. 🙂


Achievement Unlocked: 75 Watt Class A Zero Feedback SIT Circlotron

Soft clipping at 75W

Because of the high input capacitance of the 2SK180’s and the gain of this circuit, we have to pull out all the stops to get our 75W beast to make audio bandwidth. Here you can see that each SIT is getting its own transformer and buffer.






Here’s the 75 Watt V-FET prototype on the bench. More wires than Keith Emerson’s Moog! Edit: Just a few days after I wrote that caption, Keith Emerson passed away. RIP Keith. Thanks for all the music.



Here’s the THD at 1W and 10W 🙂

Here’s the simplified schematic for V-FETRON. There’s a 20 Watt version and a 75 Watt version. I think I’ll give them clever names like: V-FETRON 20, and V-FETRON 75. The 20 Watt amp uses either 2SK82 or 2SJ28. The 75 Watt amp, created for our friend Tim, uses 2SK180. I have a few more transformer types on order to evaluate, then I’ll let you know how I addressed some of the various issues involved. Muhahahaha, more later.


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