Darkness
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Do it Yourself
Darkness
DarknessFrom detritu--(at)--x.netcom.com Tue Oct 22 09:25:45 CDT 1996
From: detritu--(at)--x.netcom.com(Lord Valve)
Newsgroups: alt.guitar.amps
Subject: Why Don't We D-Do it in the Dark...
Date: 22 Oct 1996 07:00:46 GMT
X-NETCOM-Date: Tue Oct 22 12:00:46 AM PDT 1996
It occurred to me that some folks might not know these tricks, so...
Bias...
Whatever method you prefer, here's a tip that may save you some grief
down the road: When installing a new set of tubes, wait until
night-time. Put 'em in, bias 'em up, and turn off the lights. Wait
for 10 full minutes, until your eyes are fully adjusted to the dark.
Then, observe the plates in the output tubes. You can sometimes find a
hot-spot that indicates trouble down the road, or observe that the
whole set is running hot; regardless of the specs, you might want to
back the current off a little. Many times, these hot-spots just aren't
visible in normal room lighting, and especially not in the lighting
many techs use on the bench. (I use a whole lot, I'm damn near blind.)
Arc-hunting...
Another thing to do in the dark: Chasing arcs is always a bummer...
sometimes, you have one that's caused by a wire broken inside the
insulation, or one that's between the fiberboards, or even one inside a
cracked resistor; I even found a coupling cap that was arcing
internally this way... Again, power up the amp and turn off the
lights. I like to do this with a test load connected, so you can
possibly HEAR the arc as well as see it. After your eyes adjust to the
dark, beat the chassis with a rubber hammer. (I also occasionally
excite the chassis with a finishing sander...after removing the
sandpaper, of course.)
If anything's sparky, you're gonna see it plain as day. Even arcs
inside wire insulation and components emit enough light for you to
plainly see them, once your eyes are sensitive enough. I once found an
arcing standby switch in an old Marshall with this technique, after it
had flummoxed damn near every tech in town. As for arcs between
fiberboards, sometimes you can see the light that's emitted outwards
>from the crack; if not, get as close to edge-on as you can when you
observe them.
By the way...be DAMN careful where you put your fingers when the lights
are out. (Ouch!)
Fat Willie
detritu--(at)--x.netcom.com
(Lord Valve)
STILL not as big a sumbitch as folks may say...
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