DRIVE SPEED: Alps vs. Shugart Disk II (update)

[buggie@musca.unm.edu (stephen e buggie)]

I wrote an article in II ALIVE (Summer 1996, Fall 1996) describing my 
enhancements to Disk II and its clones.  The enhancements are BUGG-SWITCH 
(3-way write protect switch) and BUGG-KNOB (front panel speed adjustment 
knob).  These features will be added to your drive for $5 each, both for 
$9.00, plus return shipping cost.  Or, but a drive with both features, 
$24 plus shipping.


WILLIAM WINGFIELD wrote an article on DRIVE-SPEED CONTROL in COMPUTIST 
magazine in the late '80s.  Privately by e-mail and in person, I'd been 
bragging that Wingfield's article was filled with technical errors and 
that his circuit design would not work.  My original circuit was simpler 
(therefore elegant) and actually worked.  Wingfield's design called for 
an awkward array of buffering resistors that was unworkable.

My criticism of Wingfield's design was harsh.  Now, I realize that his 
design does work, but is limited to the rare SHUGART mechanism used in 
some early Disk ][ drives and clones.  The drive-speed hack is focused on 
the Disk ][ daughterboard, and the Shugart mechanism has a very different 
circuit than the more common ALPS drive used in 90% of Disk ][s.

Wingfield's design, presented in his article, replaced the 5K ohm 
adjustment potentiometer with a front-panel 1K ohm potentiometer, buffered
on each size with 2K ohm fixed resistors. This arrangement works on 
Shugart Disk ][ full-height drives, only.

My BUGG-KNOB circuit is simple and applies to ALPS mechanisms:  Desolder
the 50K ohm adjuster from the speed daughterboard, noting that only two
solder points are used.  Then solder the 5K front-panel potentiometer IN 
SERIES with the 50K daughterboard resistor.  The series circuit allows 
perfect centering of the front-panel potentiometer because the 
daughterboard adjuster becomes a trim-adjuster.  That's it!


So, William Wingfield, if you are reading this, I now acknowledge that 
your circuit published in COMPUTIST was correct, but it works only on 
rare Shugart Disk ][ mechanisms.  My series-circuit for speed control 
works on ALPS mechanisms used in most Disk II drives, and likely will 
work on ALPS mechanisms in other drives such as Disk IIC, platinum 5.25 
drive, DuoDisk, etc.

I'd write to author William Wingfield directly, except that no address is 
available.

Stephen Buggie	200 College Rd	Gallup NM 87301	      buggie@unm.edu