Acoustat Trans-Nova Twin-200 biasing

[EchoWars]

Tweaking one up for a buddy, and I've got a schematic, but no information on bias setting. This MOSFET amp uses three pairs of 2SK135's/2SJ50's on each channel, and no source resistor. There is a fuse on each of the +/-72V rails, so I can pop out a fuse and measure the total current going to all three devices.

At the moment, there's about 330mA crusing through the output stage (so about 110mA per device, if they're shaing well). Is that about right? Or should it be set to something else?

 

[anatech]

Hi Glenn,
That's in the ballpark. I think the target value is 100 mA per device, so 300 mA in yours.

Are you smiling yet?

-Chris

 

[EchoWars]

Smiling through chattering teeth after shoveling the driveway and walk...all that wonderful snow you sent down here.

Nice sounding amp for sure. I like it. Simple, but blown transistors would be a problem to locate. I dunno how familiar you are with this, but its the first 100% MOSFET amp that I've looked at. Very simple design, but with a wierd 'Delta-Y' thingie (tech-term) in the feedback loop. Seems to do the job though.

I heard that these are supposed to be 'The Thing™' for difficult loads...

 

[anatech]

Hi Glenn,

Smiling through chattering teeth after shoveling the driveway and walk...all that wonderful snow you sent down here.

No. You guys are sending it this way. It's been around 50 ° for a week here (in US measurements). It's just starting to get cold now. But don't worry. It will get miserable around here soon enough.

I didn't like the sound of it at all. It has it's own sound for sure, and not my cup of tea. KBK has one.

-Chris

 

[ilimzn]

blown transistors would be a problem to locate.

Not too much of a problem if you are willing to mount TO3P devices instead of TO3 (which is possible in most cases)...