On Tue, 17 Nov 2009 19:21:10 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Jim Lesurf wrote:
Could be class H. This is a power saving scheme that uses two power
rails - one low for normal listening, and a higher one that gets
added on when the power requirement is higher.

Right - but if you removed the 60 volts you'd get no output?

So the lower voltage is only for the earlier stages? OK, not class H
then.

Hard to guess without the diagrams, etc. But two things came to mind here.
One was that the output stage has voltage gain. e.g. bipolars with
collectors to the output and emitters to the rails. The other was FET
devices with an aburdly high resistance or minimum source-drain
requirement. However I'm also wondering... does the above mean *only* +60
for the output and not +/-60?... Curious.

Here's the diagram of the offending amp.
http://s139.photobucket.com/albums/q...kies/A2070.jpg

Ah, they have followed the application note in the data sheet

http://www.datasheetcatalog.org/datasheet/nec/UPC1225H.pdf'

pretty well. They have dropped some of the good stuff, though, that
could well do with going back in. The output stability choke and
resistor plus Zobel network, for example, which you will find on page
10. Anyway, there are not too many bits to check, the bases and
collectors of all those transistors will do, and compare them with a
good channel. Most likely it is the IC that has keeled over.

d