Tape thickness ... I'm so confused!

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famous beagle

famous beagle

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Ok, so, this is from my Fostex R8 Owner's Manual:

"The R8 is designed for exclusive use with 7 inch or 5 inch reels. Since a 7 inch reel of 1 mil (35um) tape is 550 meters (about 1800 feet), the maximum recording/playback time is approximately 22 minutes.

The bias and equalization of the R8 have been factory aligned for use with Ampex 457 or equivalent high-quality tapes (such as Scotch 227).


So I thought, "Ok, I need 1 mil tape, equivalent to Ampex 457." But then, after having an issue with playback speed (as described in my thread "Fostex R8 issue... please help"), I downloaded the R8 Service Manual. And it says this:

Tape:
1/4 inch (6.35 mm) tape width, 1.5 mil (35um) base
AMPEX 457 or equivalent


First of all, why does this say 1.5 mil when the owner's manual says 1 mil? And also, why are two different abbreviations used for millimeter (mil and mm)?

And to make things more confusing, this is from RMGI's site:

SM911 Tape
This is the excellent RMGI SM911 from Holland. The choice of archives worldwide (along with ATR Master Tape), this precision slit and coated tape is similar to 456 in operating level (+6) ... Each tape is 1200' in length of 1/4" 1.5 mil back coated tape on a standard RMGI 7" plastic reel. ... Bias Compatible with 456/457

and then, LPR35 Tape
This is the 1 mil RMGI LPR35 and is similar to AMPEX 456 and SM911 in operating level (+6). Each tape is 1800' in length of 1/4" 1 mil back coated tape on a standard RMGI 7" plastic reel. ... Bias Compatible with 456/457


So ..... my question (aside from the few above) is this:

Can the R8 accept either 1.5 or 1 mil thickness? And is the 1.5 mil thickness only available in 1200 feet rolls (on 7" that is)?

Thanks
 
I'm not honestly sure what 1.0 mil is short for, but it's certainly not millimetres.

1.0 mil tape on a 7" spool will run to about 1800ft, 1.5 will be 1200. 2400ft goes on a 10.5" metal spool which the R8 can't use.

I've run an A8 on 456 tape before, so you probably could use SM911 at a pinch, but the LPR35 tape is a lot closer to what the machine was designed for, and you'll get more recording time per reel (24 minutes vs 16).
 
I could be wrong but i was led to believe that 1 mil is a thousanth of an inch.
Dont ask me where i saw that. I've read so much on tape lately i don't know my arse from my elbow.
 
Ohhh ok ... I didn't know that about the "mil" and "mm" thing.

So ... I have the RMGI LPR35, and that should be good then, right?
 
famous beagle said:
Ohhh ok ... I didn't know that about the "mil" and "mm" thing.

So ... I have the RMGI LPR35, and that should be good then, right?
Click to expand...

Yes. Somewhere in the quotes above is a typo, 457 is 1.0 mil tape. There is debate here as to whether or not you can/should use 1.5 mil tape on the machines designed for 1.0 mil tape, like the Fostex narrow gauge machines. You will be technically out of spec for wow/flutter, and the tape may not ride across the head as well, so you may have some freq response degradation. I've never had a problem w/ running thicker tape on e.g. a Teac A-3300SX. However, the Fostex transport isn't all that stout, so I'd recommend you stick with LPR-35, or NOS 457. (Note also, you want NOS Quantegy 457, or Ampex 457 manufactured after 1995. )
 
famous beagle said:
Tape:
1/4 inch (6.35 mm) tape width, 1.5 mil (35um) base
AMPEX 457 or equivalent
Click to expand...

This is simply a typo in the service manual or... possibly they are using the measurement of what the tape thickness actually is after the oxide and backcoating are applied... 35um (micrometers), which is closer to, but not quite 1.5 mil. 457 is considered 1.0 mil referenced to base-film thickness before oxide and backcoating are applied and that's how most tape companies measure tape thickness. One exception was Maxell. UD 35-90 (35um x 90 minutes) would be considered 1-mil tape by Ampex/Quantegy because the base film is about 1.0 mil. So Fostex is really confusing the issue here by expressing thickness in terms that Ampex never used. Nor did 3M/Scotch, AGFA, or BASF/EMTEC. However, hardly any tapes have a base-film thickness of exactly 1.0 mil or 1.5 mil. It's just an approximation for general category. Otherwise the numbers would be all over the place, which would be difficult from a marketing perspective.

Base-film matters most with tapes that have both 1-mil and 1.5-mil versions because the oxide and backcoating are the same thickness. For example, 456 and 457 have the same amount of oxide and backcoating.
 
Does this help:

mil (ml)
A unit of length in the US Customary System equal to 1/1000 of an inch (0.03 millimeter), used chiefly to measure the diameter of wires.

Don't forget that the total thickness is the Base film + Oxide coating + Back coating.

Cheers

Alan.
 
I used to use a Fostex R8 and I always used either Quantegy 456 or RMGI SM911 tape. I tried out the thinner tape (457 or Zonal) and it didn't seem to run as well. I know that this machine is designed to run with the thin tape but it sounded better and had far fewer dropouts (which are a constant fear when using the R8) when using 456 or SM911. The worst tape was definitely the Zonal. I got loads of dropouts and the sound was not very good. I watched the tape running through the machine and it seemed to be terribly slit. It was riding up and down the heads where the 456 seemed to stay completely still.
 
Beck said:
This is simply a typo in the service manual or... possibly they are using the measurement of what the tape thickness actually is after the oxide and backcoating are applied... 35um (micrometers), which is closer to, but not quite 1.5 mil. 457 is considered 1.0 mil referenced to base-film thickness before oxide and backcoating are applied and that's how most tape companies measure tape thickness. One exception was Maxell. UD 35-90 (35um x 90 minutes) would be considered 1-mil tape by Ampex/Quantegy because the base film is about 1.0 mil. So Fostex is really confusing the issue here by expressing thickness in terms that Ampex never used. Nor did 3M/Scotch, AGFA, or BASF/EMTEC. However, hardly any tapes have a base-film thickness of exactly 1.0 mil or 1.5 mil. It's just an approximation for general category. Otherwise the numbers would be all over the place, which would be difficult from a marketing perspective.

Base-film matters most with tapes that have both 1-mil and 1.5-mil versions because the oxide and backcoating are the same thickness. For example, 456 and 457 have the same amount of oxide and backcoating.
Click to expand...

Ive never had a problem that I remember of back when i was using 456 are 499 , didnt even bother knowing are caring what the milimeter was,tha only one i was concerned about were on cassette,I always used the shorter lengths cause always was told it was a thicker mil. and less likely to get "ate up" buy the transport......needless to say i had no troublw whatsoever with either format(RR or Cassette) and cant wait to start making music with all of my analog gear again !!!
 
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