"Gregg" wrote in message
news:8rFMd.555$rB6.134@edtnps91...
Behold, Tim Williams scribed on tube chassis:

snippage

Steel is stronger, cheaper and all the other things that usually go with
it (like solderability).

Exactly!

Steel can encourage the "ground it anywhere" technique - what we want to
try and avoid :-o

Oh Greggggg...
Just 'coz one can stick a pencil in his eye & poke it out, does it mean that
we should stick to real soft crayons?
Sure, it's possible to go very wrong with steel, but one can go just as
wrong with aluminum, if not worse. Most production gear relies on steel
chassis, and even uses those chassis for ground systems (when you're going
to mass-produce something, you can spend some R&D time figuring out just
*where* on the chassis the grounding points should be, and do what so many
manufacturers do (err... did.) - punch out little lugs at the precise points
where the ground points are. requires a bit of thought, but hey - try
bettering that ground scheme, & you'll, most likely, find out that you
can't.
And hey, you could think of the steel as an electromagnetic shield, if you
wish. If the chokes /transformers are stood off by as little as 1/8 of an
inch (something which is not often done in cheap gear, economic reasons),
you can avoid the nasties you get with transformer cores *touching* the
steel, if steel hardware is used (which is, strangely, not always the case),
you could avoid creeping electrolysis, which makes aluminum chassisage weird
& generate intermittent problems. That white powdery stuff is a good
insulator, you know...
There's all kinds of stuff in favor of steel, even if you forget cost &
resistance to fatigue (Tim the child-pilot could tell you about metal
fatigue in aluminum plane parts, and how thousands of rivets have to be
drilled out & re-riveted when old planes are brought back up to being
flight-worthy... The special primers needed to prevent corrosion & make any
paint stick.
This, of course, is all moot for folks like us, who can't afford chassis
punches, modify the layout 20 times, and have crap for tools (I use a
carbide-tipped table saw to cut & do basic horizontal milling on aluminum
plate, and use a regular plunge router to cut clean holes & as a substitute
for a vertical mill (neither recommended - even if you're good, you'll hurt
yourself eventually - I did, more than once). The stuff cuts nicely,
there's always a good supply of plate from both metal salvage & dumpsters,
small square stock could be used for joining plates together (look at any
one-off chunk of early lab gear - gorgeously done chassis without any use of
metal breaks), etc., etc.
Of course, I always stuck with steel for guitar amps, which have a totally
different set of requirements. Nothing beats a welded steel chassis
there...