So lets say you have an extra Amplifone vector
monitor and a Tempest that needs a vector monitor. The only problem is,
all Tempests were designed around the Wells Gardner 6100 monitor. While
the 6100 and the Amplifone are pin compatible, the Tempest PCB compensates
for the pincushioning that was inherent in the 6100 design. Wells Gardner
vector displays (such as the WG 6100, 6102, and 6400) use a slightly concave
CRT. Combined with the neck configuration of the tube, this results in a
visible "bowing" effect where the side of the screen appears to
pinch inward where straight vertical lines should appear. The Amplifone
vector monitor does not have this "bowing" and therefore the games
designed for these monitors (Star Wars, Quantum and Major Havoc) do not
have this correction circuit built in to the PCB. Additionally, there is
no actual "correction circuitry" in the Amplifone, it was done
through a combination of tube design and yoke design. Mostly the yoke.
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Disabling the pincushion correction on the Tempest PCB is pretty easy.
Jed Margolin suggested connecting R141 and R161 to a fixed voltage rather
than A/B13 pin 14 and A/B12 pin 14 in the XY output section. The voltage
you need is about 10 volts. Conveniently enough, R142 and R160 provide
a 10v source you can tap into.
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So, if you look at the picture on the right, you will see that all I've
done is jumpered the two resistors together thus disabling the pincushion
correction. Measure pin 4 of C12 and C13 before and after you make the
change, it should be around 2.05v. The difference is pretty small, but
you may consider putting a 10k pot in place of R141 and R161 to determine
exactly what resistor to use in order to make the voltage the same. I
would also suggest not plugging the monitor in while doing it.
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(click for a larger image) |
| After making the change, you'll probably need to adjust the
XY-linear pots because you're lines may not be exactly straight. One other
thing you might want to know, I used a Wells Gardner monitor frame to mount
the tube. I'm sure any 19" frame would work though. The Amplifone tube
is also slightly longer than the Wells Gardner, but you can still close
the door with about an inch of clearance. Zonn told me someone (i.e., he)
banged the door into the tube on his game and broke the neck. Ouch. Just
something to watch out for. |
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