[Arny Krueger]

wrote in message
oups.com
It seems that you have do have different schematics to
the one that is in my SP8 manual. I looked at the one on
the ARCDB and it is from a later version. From the
photos on that website it seems I have a Mark I preamp. I
don't know whether it's revision 2 or 3, but the
schematic does mention changes made in 1981, so I would
assume it's not the original version - called revision 1
on the ARCDB (although how the first version of something
can be a revision, I'm not sure!).

Anyway, my manual does not show this resistor no. 27 in
this position. Rather, resistor 28 is in a similar place
to resistor 83 and there is shown a line parallel to it
that has a gap in it. The lines end in circles with
crosses in them similar to the ones at either end of your
r27 on the ARCDB site. This is the place where it says
that r29 should go if needed. I also note that the gain
reduction quoted here is 10 dB's rather than the 6dB's
mentioned for my 39.2k resistor.

If you look at the photo of the Mark 1 SP8 internals on
ARCDB you can see the bottom of 2 of the posts I was
referring to where they protrude from the other side of
the double sided circuit board. Frustratingly, there is
no photo of the underside of the board & mine is very
different from the underside photo of the later amp that
is shown.

Here's how you find them:
If you locate the yellow Wondercap to the far left, below
the mains transformer, you can see the shiny edge of the
heat shield I referred to. Now, between the Wondercap
and the heatshield there are 4 solder tracks that go
under the cap. The left hand one goes under the left
hand end of the cap, leaving 3 more going under the upper
edge of
it. The track to the left and the one to the right show
the bottoms of these posts as shiny discs. I think r29
should be soldered across these posts because I measured
the resistance between them and found
39.2, which I assume to be the value of the paralled
resistor, r28. If you then look to the right of these
posts, there is a black resistor with its left hand wire
going into a spot of track with no begining or end - I
think this is r28.
If you want to see what the posts look like from above
there are two more over near the top of the amp between
the topmost psu capacitor (one of the upright ones) and
the transistor mounted in the heatsink. There is a black
device soldered between these posts - not sure if it's a
resistor or not. The lower of the two posts is easier to
make out than the other one.

I wonder if anyone looking at this has a similar vintage
SP8 with a resistor across these posts on their amp?

Probably not anybody who posts here regularly.

It appears to be that you are either underequipped, undertrained, or too
timid. If the shoe fits there are probably skilled professionals who can
serve you.

If you've got some traces on a circuit board that go who-knows-where, you
can always power the unit up, maybe send a tone through it, and probe around
with a scope and/or a meter.