Re: Apple 5.25" drive vs Unidisk 5.25"

["Michael J. Mahon" <mjmahon@aol.com>]

Roger Johnstone wrote:
> In <0tGdnaAuM5HTdwHZnZ2dnUVZ_uqdnZ2d@comcast.com> Michael J. Mahon wrote:
>
> > rob wrote:
> >
> > > What are the differences between these drives apart from the Unidisk
> > > requiring 12v ?
> >
> > There isn't any difference, except daisy-chain cabling and the case.
> >
> > Both require +12v., +5v, and -12v.
> >
> > -michael
>
>
> Hmm... I remembered reading that the reason the Apple IIe card for the 
> Macintosh LC could only use the Apple 5.25 Drive for its 5.25" drive was 
> that the Mac LC didn't have a -12V supply.
>
> This article claims that's the reason.
> Apple IIe Card: Which Drives are Supported
> http://docs.info.apple.com/article.html?artnum=8807
>
> But then this one says the drive does need -12V.
> Apple 5.25 Drive: Specifications
> http://docs.info.apple.com/article.html?artnum=7886
>
> But then again maybe it's just an incorrect copy and paste of the 
> specifications of the older drive.
> UniDisk: Specifications (Discontinued)
> http://docs.info.apple.com/article.html?artnum=1189
>
> I suppose I could satisfy my curiosity by opening up one of those Apple 
> 5.25 Drives by my feet...

Actually, the only thing that -12v was *ever* used for was to allow a
bias adjustment for the head amplifier to go both positive and negative.

If Apple switched to a different head amplifier than the MC3740 (?),
they could have dispensed with the -12v supply.

-michael

Parallel computing for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

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