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<p>It was a photo process using high contrast film and photo-resist.</p>
<p>You'd actually use red, blue and black tape on a clear mylar
sheet. We'd also always do our boards at 2X resolution too. Traces
on both sides of the board were done with black tape, one side
with red tape and the other side with blue tape. You'd take the
layout somewhere where and they would make a 1X high contrast film
(can't remember if negative or positive) for each side. They'd use
red light to make the black and blue traces come out on the film
for one side and blue light to make the red and black traces come
out for the other side's film.</p>
<p>You'd then take the films and put them on a board with
photo-resist, expose with UV light, etch and plate. Can't remember
where in the process drilling and through-hole/via plating was
done.</p>
<p>Jay S.<br>
</p>
<div class="moz-cite-prefix">On 2/14/2020 3:14 PM,
<a class="moz-txt-link-abbreviated" href="mailto:rsdio@audiobanshee.com">rsdio@audiobanshee.com</a> wrote:<br>
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cite="mid:CAE84779-9499-49BD-89DB-532BF21D7D85@audiobanshee.com">
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<div class="">Is there any documentation of the black versus
red/blue Mylar tape process?</div>
<div class=""><br class="">
</div>
<div class="">I’ve long assumed that the curved traces were
hand-drawn with solder resist pens, or some other, similar
process that was mostly manual. I also assumed that Mylar was
cut with X-Acto blades. How would the black “crepe” tape be cut?
… and how is the width controlled?</div>
<div class=""><br class="">
</div>
<div class="">Despite the obvious pedantic tendencies, I actually
believe it would be historically important to document these old
processes. It seems that a number of computer history museums
are gathering documentation of these early events, and I’d like
to see PCB design as a part of that effort.</div>
<div class=""><br class="">
</div>
<div class="">Brian</div>
<div class=""><br class="">
</div>
<br class="">
<div>
<div class="">On Feb 14, 2020, at 11:39 AM, Harry <<a
href="mailto:hbissell@wowway.com" class=""
moz-do-not-send="true">hbissell@wowway.com</a>> wrote:</div>
<div class="">
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<div class="">
<div dir="auto" class="">Ok most of that is hooey! The
curved traces were because the layouts were done with
black "crepe" tape on Mylar. Curves are easy to do. That
was superseded by red/blue Mylar tape which does not do
curves. In short, for audio frequencies there will be no
difference. A good two layer or multilayer board would way
outperform anything from the 1970's. <br class="">
<br class="">
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<blockquote type="cite" class="">On Feb 14, 2020, at 2:10
PM, Harry <<a href="mailto:hbissell@wowway.com"
class="" moz-do-not-send="true">hbissell@wowway.com</a>>
wrote:</blockquote>
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<div class="">
<div dir="auto" class="">
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<div dir="ltr" class="">
<div dir="ltr" class="">
<blockquote type="cite" class="">On Feb 14, 2020, at
1:50 PM, Jimmy Moore <<a
href="mailto:jamoore84@gmail.com" class=""
moz-do-not-send="true">jamoore84@gmail.com</a>>
wrote:</blockquote>
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<div dir="auto" class="">
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<div dir="ltr" class="">
<div dir="ltr" class="">This came up on the AH
"behringer RD-6" thread:
<div class=""><br class="">
</div>
<div class="">>>Until the PCB traces are
curvy (like on a 2600 or SEM) it's never going
to sound authentic. Electrons don't like
corners.</div>
<div class=""><br class="">
</div>
<div class="">I had picked up similar folk
knowledge from my first engineering job working
alongside techs, EE's, and designers. I went
looking for a more technical explanation on why
this is the case, and it turns out it is NOT: </div>
<div class=""><br class="">
</div>
<div class=""><a
href="https://resources.altium.com/pcb-design-blog/pcb-routing-angle-myths-45-degree-angle-versus-90-degree-angle"
target="_blank" class=""
moz-do-not-send="true">https://resources.altium.com/pcb-design-blog/pcb-routing-angle-myths-45-degree-angle-versus-90-degree-angle</a></div>
<div class=""><br class="">
</div>
<div class="">(Notable exceptions being RF, high
speed, or high voltage layouts)</div>
<div class=""><br class="">
</div>
<div class="">This and <a
href="https://electronics.stackexchange.com/questions/226582/pcb-90-degree-angles"
class="" moz-do-not-send="true">another</a> resource
debunk the pcb corner myth on EMI effects. </div>
<div class=""><br class="">
</div>
<div class="">Is there any other tangible
(audible) impact this decision could have for
music electronics? I think not, but I'd love to
hear from other more experienced engineers on
this (hopefully not tiresome) topic.<br class="">
</div>
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