Another bias question (logging tape vs grand master)

[Blue Jinn]

I didn't want to hijack the other thread. But the "logging tape" question has been making me think.

Here are the published specs for several Ampex/Quantegy tapes.

8206:
Coercivity 350 ±10% Oe (27.9 ±10% kA/m)
Retentivity 1260 ±10% Gs (140 ±10% mT)

632:
Coercivity 310 Oe (24.7kA/m)
Retentivity 1100 gS (110 Mt)

406:
Coercivity 330 Oe (26.3 kA/m)
Retentivity 1300 Gs (130 mT)

456:
Coercivity 320 Oe (25.5 kA/m)
Retentivity 1500 Gs (150 mT)

499
Coercivity 350 Oe (27.7 kA/m)
Retentivity 1650 Gs (165 mT)

GP9:
Coercivity 370 Oe (29.5 kA/m)
Retentivity 1600 Gs (160 mT)

I've always read that 406 and 456 are 'bias compatible' or 'interchangeable' except for levels. Same with 632. IOW that if a machine is calibrated for 456, you can use 632 or 406 without re-biasing as long as you mind the level.

Question 1: how close is close enough? With 632/456/406 being "compatible" +/- 10 Oe but 499 at 350 requiring a rebias.

Question 2: Based on the above, it looks like the logging tape would be fine on a machine biased for 499, but at +3 instead of +9. On paper it looks like, with noise reduction, it would be a fine tape for music.

Yes/no/maybe?

 

[RFR]

I dunno but I have bunch of 406 and now some logging tape. I hope it’s ok