Power scaling redux
I admit it: I can be stubborn. Hard headed, even, and I sometimes to refuse to give up when wiser folk would have walked away from a problem. Such it is with power scaling. I really, really want power scaling to work with the DC30. Yeah, the amp has separate volume controls for each channel and a master volume but I want more. I want good tube amp sound at low volumes, the kind of volumes I might play in my living room late at night when my kids are sleeping upstairs. I want power scaling.
The information included in the power scaling kit just wasn’t enough so I spent a ton of time yesterday and today on the 18Watt site, scouring the power scaling threads, trying to get a clue how I might get it to work. I discovered answers to a couple of my big questions in the “poor man’s power scaling” thread. Specifically, I re-read some of Mickey posts and realized that the output transformer is scaled along with the power stage of the amp, and the B+ voltage for the output transformer is taken just before the power stage filter caps. One mystery solved.
I also figured out that I could use the stock Ceriatone filter caps for the preamp stage and use separate filter caps and resistors for the output stage. Why didn’t Kevin O’Connor include this in his documentation??? Regardless, the poor man’s power scaling thread also linked to some good schematics that got me thinking and moving in the right direction. (Join the 18Watt community if you want to take a look.) I’m still going to use the second Ceriatone filter cap board piggy-backed on top of the stock board, but instead of including all the filter caps, this board will house the power scaling components and filter caps for the output stage.
Here’s what it will look like:
Much cleaner than my previous layout.
And, instead of crucifying a second turret board, I ordered up a proper turret staking tool and large turrets from TurretBoards.com. These, along with a more resistors, zener diodes and mil-spec 2W potentiometers from Mouser should be here this week so I can have a clean go at power scaling.
‘Cause you know I will get this working.