"Alex Bird" wrote in message
oups.com...
Arfa Daily wrote:

I personally, have never had a problem here with counterfeits, as far as
I
know, although I did have a problem just this week, with some 7915's.

One guy had opened the cases of some and found the silicon die to be a
quarter of the size of the proper part, they didn't last very long!


The emitter resistors that I referred to, are usually white ceramic
square
bodied types, rated about 4 watts,

Ah, I think I knew at the back of my mind I should have checked them.
The night was wearing on, I got the amp for nothing, and I skipped
ahead to the substitution.

I'll check it out.

As far as the bias goes, I would not expect there to be much difference
between the original failed transistors,
snip However, when you fit the new ones,
they may have significantly different characteristics, and require the
bias
to be set.

Especially as I cannot get the original part, I'm still not sure what
the best replacement pair is. The part numbers in
my original post turn out not even to be a pair!
If I could find a data sheet for the originals...
I've emailed grandata anyway to see if they can suggest.

In general, if the heatsink temperatures remain about the same to
the touch between the channel with original transistors in,
snip
Hope all this is helpful to you

Yes, much appreciated. I know I'm not the first person to open this
amp, so I'll probably be checking out both channels.

Could I feed a tone in and tune it looking at a spectrum display? The
one I have is basic but fine for audio.

Alex


Yes, you could do that. Any serious distortion would soon show up as
harmonics. Providing the generator produces a reasonable sine wave, you
could also look at the output on a 'scope, paying particular attention to
the zero crossing, where you will see the bias setting having most effect.

Arfa