On Tue, 25 May 2010 18:49:19 -0700, David Nebenzahl
wrote:

On 5/25/2010 4:39 PM Paul G. spake thus:

That's funny.... when I was visiting my daughter in Ottawa, I
spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed
a Techics (!) "new class A" amp, and a Technics CD player, and
stuffed them in the trunk of the car for the 1200 mile return trip.

Hey, my current amp is one a'them Technics "new class A"s, a SU-V6X.
What's yours? Got mine really cheap years ago at a Starvation Army store.

Mine's a SU-V7B. I imagine there's not a lot of difference... I used
the schematics for SU-V98 to change some of the circuitry. That was
the only close schematic I could find on the internet. It wasn't quite
the same, but the reference designators (like R520, C123) were good
enough to locate things.
The original fan was irritatingly loud... I can't imagine how
anyone could put up with it.
It uses a hybrid module to drive the output, and I imagine only
much earlier models would use discrete transistors. I found it to be a
surprisingly powerful amp for class A, but their "new Clas A" just
slides the biasing up and down so that at low power it's still class A
but biased low enough to stay cool. There is an art to doing that, and
keeping the system well behaved and linear. I imagine there could be
problems if the amp is biased for quiet music, and a sudden loud
passage comes along that requires fast changing the operating point.
There are probably a good number of patents that relate to that bias
circuitry.
I've had no complaints about it, except for having to replace the
on-off switch (a low power switch that controls a relay which switches
the AC line). Because of the weird shape of the switch, and it being
alternate action, I had to jury-rig a small toggle switch with an
extension on its handle.
I used ductape to channel the air flow over the heatsink, to
improve the cooling. Running full output, the heatsink doesn't get
overly hot, and the exhaust air is quite warm. The fan I used was a
12v small quiet fan, similiar to those used on smaller CPU's.
Typical for much electronics, it's the mechanical stuff that seems
to fail first, or isn't properly designed to last.

Paul G.