Claim that 641/642 similar to 406/407

[Blue Jinn]

Found this on TapeOp.

"A great example is Ampex 641/642, a tape which Steve Smith at Ampex/Quantegy verified is "very, very close in construction to 406/407" (a notorious tape for sticky shed) but without backcoating. Mr. Smith verified some years back that the oxide binder used in these two tape lines was essentially the same. 641/642 tapes of the exact vintage 406/407 from the 70's do NOT exhibit sticky shed, and you can read all over the web regarding comments that state "600 series tapes never shed and are if nothing else, reliable."

I don't know if the author is mixing up 632 with 641. But I found this interesting.

 

[drrats]

bump for a super old thread! Anyone care to speculate further on this?

 

[pdmillar]

632/642 (1.5 and 1mil) are low-output (185nWb) 1960s kind of tapes. They continued making them right up until the end of Quantegy. As far as I know they do not stick or shed, but the oxide formula is definitely NOT equivalent to 406 which takes more bias and has a 3dB higher operating level (250nWb). My experience mixing stuff to some NOS 80s or 90s 632 tape I had a while back was that the saturation characteristic was distinctively softer and "pillowier" than the "modern" +6/9 type tape I usually use - probably a lot of hi-freq self erasure or something. Definitely would recommend trying it if that's the sound you're after and don't mind a bit of hiss.

 

[ethyrvalve]

John Klett's archive has the tech specs for both:
http://www.technicalaudio.com/pdf/Quantegy_tape/Quantegy_600series.pdf
http://www.technicalaudio.com/pdf/Quantegy_tape/Quantegy_406_407.pdf
Not sure how similar the chemistry is but the oxide coating thickness is very different (7.9µm for 632 vs 10.1µm for 406).
I really like 632 but like pdmillar is said, it is a lower output/lower headroom tape.
However I've had the opposite experience with hi-freq response. I think 632's thin coating helps it have a very good 'head wrap' which can lead to an elevated treble response (on some old machines, like my Ampex AG350, you cannot turn the record EQ down enough to get a flat repro without modification) and this extra record treble can be your friend when it comes to hiss (you can roll off the highs a little bit when you mix and it might still be flat).
I haven't tried 632 on a 388 but I suspect it might be quite overbiased which would make it dull-sounding (and hissy if you try to brighten things after the fact) without recalibrating the bias (not fun on this machine). Another minor nuisance is the the lack of backcoating makes the tape really static-y in some situations.

 

[drrats]

Excuse my ignorance but why is static a bad thing?

 

[pdmillar]

Static discharge is heard through the repro amplifiers as pops/clicks. Seems to happen more often with poor quality cassettes. The backcoating on studio tapes has a finite amount of electrical resistance by design to prevent static from building up.

 

[drrats]

yeah okay that makes sense. What do you people do to minimise the static on non-backcoated tape? Or can nothing be done?
also... nice sounds on the bandcamp btw

 

[lonewhitefly]

Best thing to do might be to grab a handful of different tapes on eBay (they're cheap and you can get them in lots sometimes) and try them on your 388. Of course, avoid sticky shed tapes like Ampex 456/406, and Scotch 226 ... but non-backcoated tapes generally will not give you serious trouble like that (though some have their own set of issues).

All of this stuff can be unique. Different tape formulations with different bias settings on different tape decks can perform differently. I didn't like mixing to Scotch 206 on an Ampex AG-350, yet I liked it for multi-track recording on my 8-track version of a similar machine (AG-300). 202 was my favorite on my Ampex 440 mix decks, but didn't suit the Teac 3300 in my opinion. I also didn't like the few examples I played around with of those old non-backcoated Ampex tapes as much as the Scotch ones.

You never know, you might discover something no one else has found yet.