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Original Message

RE: Was: Re: PAS Transformer Replacement

Posted by sbalfour on March 22, 2011 at 17:43:29:
Wow! Nice iron, dood! When I started to build my own project amp,
I did exactly that - a separate outboard power supply. My stereo rack
space limits what I can do with the existing equipment, though. For
existing boxes, everything needs to fit in the box.

But I need to make a correction to my last post in the thread, adding up
the current draw on the PA211 12V winding. The 12ax7 spec says 150ma@12.6v
for each 12ax7, and we're drawing from a 12V winding, so current needs to
be rated at the winding voltage. There are 4 12ax7's, each drawing 150ma
at the winding voltage, and it doesn't matter series or parallel arrange-
ment in the circuit. So that's 600ma for the 12ax7 filaments. Plus 300ma@12v for the rectifier, and at least 300ma@12V for the lamp =
1200ma or 1.2A. And there's still the I^2*R losses to consider. These are all resistive loads and don't depend on signal, so the current is
RMS. That indeed looks grim for a tranny rated 800ma@12v. (Norm Koren's
figures that I referenced are also incorrect - yes even the high and mighty can have a bad hair day).

Now somebody check my numbers and tell me why we aren't all having a
meltdown?
Stuart