acorec said:
From the best analog multitrack tec out there (Eddie Ciletti):
"...Note: Modern high-output tapes are not a good match for older pro or narrow-format semi-pro machines, which may not have enough current to fully erase previously recorded material. Compared to older generations of tape, modern tapes can be an additional half-mil thicker than the original "1.5 mils,"
He's not talking about the difference between 456 and GP9. This should be obvious, as 456 is not 1.5 mils thick, but -- wonder of wonders -- about "half a mil thicker." The "modern high-output tape" he's talking about
is 456.
The rest of what he says has to do with the electronics, not tape tension. Whether your deck will bias up for GP9, or has enough headroom to even use the extra headroom on the tape without the electronics distorting, is a whole different question. A great many machines that were built for 456 can.
That is an open question. As I said, not everything you originally posted is wrong ... it was about half right.
"....Professional machines have a generously wide adjustment range, and many narrow-format machines have extremely limited range. Many Tascam MS-16s do not have enough range in the bias control to accurately find the peak at 10 kHz. Most Fostex machines have a continuously variable bias capacitor. Without a voltmeter or oscilloscope, it is possible to be on the wrong side of the bias peak...."
More stuff about electronics. The fact a machine might not bias up for GP9 is a good point. Of course, you didn't even mention it in your original post.
Home machines are much tougher to align than pro machines. You really need an O-scope if you want to make the job easier (or sometimes possible).
Nonsense.
You need an oscilloscope if you want to adjust azimuth quickly and accurately. That's the case if you're using 456, or GP9, or 406, or hand-cut strips of paper rubbed with iron oxide. That's the case if you never change the tape you use. It's got nothing to do with the choice between 456 and GP9.
You can adjust bias without an oscilloscope. If you use an oscilloscope to adjust bias, all you're doing is using the oscilloscope as a voltmeter. You can use a voltmeter to do the same thing. You can use the machine's own VU meters. I'll take Mr. Ciletti's word that "it is possible" to be on the wrong side of the voltage peak when adjusting bias on "most Fostex machines." This, of course, is irrelevant to those (like the guy who asked the question in the first place) who don't have one of those Fostex machines, doesn't say either a voltmeter or an oscilloscope is necessary, and doesn't say an oscilloscope is necessary at all. Indeed, while it is slightly different from what Ciletti says, it seems that with a continuously-turning bias pot, it's possible to be on the wrong side of the peak if you
do use a voltmeter.
If you quote something, then misstate what it says, you're just confusing people.
Two head machines are the hardest to align.
That, on the other hand, is true enough. Of course, a
Tascam 32 is not a two-head machine ....
... for mix-down to stereo onto 1/4" Tascam 32 15ips. Which tape is better quantegy 456 or GP-9? Well, I know some general deal about what these tapes are. I happened to stock some 7" GP-9s ...and getting pretty good result. But it looks like 456 is couple bucks cheaper and I've seen 10" reels available. so I was thinking ...maybe 456 is the way to go... the same (similar) as GP-9 ...or maybe even better with tascam-32.? Or maybe GP-9 isn't good for tascam 32... or no big difference? ...heh heh 
The perspective of messing with calibration with my deficit of knowledge and experience with these machines isn't very sun-shiny to me 
..that's sounds like I've stockpiled wrong tape for being lazy'a%s
