Power scaling no more
Am I in over my head? I thought adding power scaling to the Ceriatone DC30 would be simple enough—hell, I bought a kit, how hard could it be? Add a couple of transistors, a handful of resistors, a pot and some additional filter caps and voila, power scaling. To say it isn’t working out as planned would be, to borrow Bill Bryson’s phrase, flirting dangerously with understatement.
Part of the problem is the “kit” from London Power. Not to slam Kevin O’Connor or London Power, who by all accounts is a great guy, but I’m not sure I would call a small bag of unlabeled electrical components and four pages of photocopied instructions—hand drawn schematics and all—anything more than the merest hint, outline or sketch of a “kit.” I understand the problem of selling a kit that needs to be easily adaptable to many different amps, either as retrofits or incorporated into a new build, since each amp has unique requirements. But the hand drawn schematics are very difficult to follow for a novice. There are also some big questions that go unanswered: If you’re power scaling only the output stage, do you power scale the output transformer or not? The instructions go into some detail about building a small circuit board to hold additional filter caps, resistors and diodes to filter the preamp section of the amplifier, but wouldn’t it be easier to leave the stock filtering in tact and add new filter caps, etc, for the output stage?
I thought I had a handle on most of these questions and drilled the mounting holes for a TO-6 socket on the chassis, and drew a layout for a small circuit board for the power scaling components. I still planned on using the second turret board I purchased from Nik at Ceriatone for the filter caps. The circuit board is only about 1.25” x 3.25” and should have fit neatly between the mains transformer and the rectifier tube sockets. There are even two small holes already drilled in the chassis—one is the 6.3V heater connections and the second is a ground point—where I could attach standoffs and mount the board. Easy right?
My first power scaling layout:
11
And the board:
Looks like crap, don’t it? This is what happens when you try to make a turret board without the right tools. Worse still, the small turrets aren’t big enough to accommodate the 20ga hookup wire I’m using. Damn, damn, damn. To further complicate things, using the existing holes means re-locating the terminal strip that connects the 6.3V heater leads from the mains transformer to the sockets and pilot lamp. But there’s no good place for the terminal strip. And I’m still wrestling with how to setup the filter caps.
I need to take a closer look at this and see if I’m missing something fundamental. In the mean time, I will probably remove the TO-6 mounting sockets and will begin the long process of changing the amp back to it’s stock configuration of a 1/2 power switch. Stay tuned….