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Author Topic: ampex 641 tape "professional"  (Read 18638 times)

Offline funbebop

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ampex 641 tape "professional"
« on: April 11, 2009, 10:59:07 PM »
Hi tape folks,

just wondering what kind of consensus with NOS sealed ampex 641 "professional" tape is for "home" recording purpose, not "mastering".

thanks in advance for any replies...

Offline ironbut

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Re: ampex 641 tape "professional"
« Reply #1 on: April 12, 2009, 01:07:02 AM »
641 was a "voice grade" red oxide tape. It is the 1 mil version of 631. It's a pretty old formulation (1960's) so it won't have very good spec's. It shouldn't have any problems with sticky shed but it wouldn't be a first choice for recording music for several reasons. It will be pretty noisy compared to modern tapes and although voice grade tape was formulated to minimize print through, it may have stretching or breakage problems because of the thin backing. The frequency extension wouldn't be anything to write home about either.
I've never used it myself but some recordists have favorite old tape to record with and perhaps this is true with 631/641. But, unless that's the case, I would guess that it doesn't have much going for it.
Like I said though, this is some pretty old tape stock and I'd worry about how it's been stored all these years.
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Offline Ben

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Re: ampex 641 tape "professional"
« Reply #2 on: April 12, 2009, 02:04:32 AM »
Do the older tapes have any specific recording speed set for them?
From what little I remember of R2R in the late 70's was Radio Shack advertising
how long the blank tapes could record rather than hi-fi quality.
I do know that pre-recorded R2R tapes was a item I never knew about
until last summer off of ebay.
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Offline steveidosound

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Re: ampex 641 tape "professional"
« Reply #3 on: April 12, 2009, 08:35:10 AM »
Do the older tapes have any specific recording speed set for them?
From what little I remember of R2R in the late 70's was Radio Shack advertising
how long the blank tapes could record rather than hi-fi quality.
I do know that pre-recorded R2R tapes was a item I never knew about
until last summer off of ebay.


To the best of my knowledge, no.
Thinner tapes - 1 mil. - .5 mil. tended to be used at lower speeds for long recording time for voice, especially on smaller reels. There were many battery portables that used 5" or even 3" max reel size.
Studios have always tended to use the thickest 1.5 mil. tape for less stretch and print through problems.
All the speeds we have now have been around since at least the 1960s. 
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Offline funbebop

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Re: ampex 641 tape "professional"
« Reply #4 on: April 12, 2009, 09:50:57 AM »
Hi Iron,

thanks for the reply...I'm finding this stuff fairly cheap and I suppose most people are looking for higher grade and thicker backing.  When did the higher grade of tape come out, like chrome tape for cassette?  And then later metal tape became available soon after the chrome?  I'm sure the price will be higher for better quality tape.  I know from many older recordings by the grateful dead they used some of the older tape and they're recordings sound pretty good.  Alot of their stuff was at 7 1/2 ips, but then later on certain projects they would upgrade to 15 ips.  I think I will still get a decent sound but with some "noise", but I do worry about breakage using 7 1/2 ips.  thanks again for the rapport

Offline ironbut

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Re: ampex 641 tape "professional"
« Reply #5 on: April 12, 2009, 11:45:23 AM »
I think it would be fun to do some tests of how well some of the tapes (pre70's) would do in a modern machine. I'm sure you're probably finding this tape for a song but like I said, this is voice grade tape and just about any other Ampex, 3M, BASF , Agfa, Audiotape etc. would be better for the demands of music recording. One of the problems that I think you'll encounter with using these older tapes is tape saturation. This is just my best guess, but I wouldn't think that they have very much headroom. I'm sure that this varies a great deal from tape to tape (type) but the amount of hiss that you find on old master recording and prerecorded r2r tapes seems to indicate that pretty conservative input levels were employed to avoid any saturation distortion. Of course, as the subscribers to the Tape Project can all attest, there is nothing wrong with the music that's contained on this old oxide.
As far as physical problems you might encounter with old tape, particularly if it wasn't stored carefully, would be loss of lubricant (drying out), warping/curling, and excessive oxide shed.

 LOL (loss of lubricant) is sometimes also called vinegar syndrome but personally, I think they're related rather than the same. Just like sticky shed, it is a change in the chemical make-up of the tape. It's easy to spot. When you first open a box or bag the smell of vinegar is evident. Many times, if it's stored in a cardboard box, when you remove the reel you'll see an image of it on the inside in a light brown discoloration. Actually, this discoloration is a good thing since it's evidence that the cardboard has absorbed the acidic acid that's been released from the chemicals in the tape (high school science will tell you that acidic acid is what vinegar is). If left unchecked, the loss of binder chemicals and the acid will totally release the oxide from the backing. I've seen pictures of sections of tape that all you can see is the clear backing in the tape path and piles of oxide slivers before the machine could be stopped. This is a very extreme case that's good for scaring restoration guys into being more careful during a first pass with an unknown tape but in reality, doesn't happen very often. What does happen is oxide shed of one level of another. In practical terms, oxide shed is more of a pain than anything else. You have to constantly clean the tape path and that's no fun.

Warping or curling is usually associated with an improper tape wind but this isn't always the case. With an NOS tape, storage is key. The tape winds are constantly trying to move to the center of the reel. Anyone whose wrapped a piece of dental floss around a finger can attest to the fact that even if you apply constant tension to the wraps, the tension at your finger increases with each one. Most of us throw away this floss in plenty of time before our finger tip turns black and falls off, but what do you think would happen if we put it on a shelf for say,.. 3 or 4 decades? For the most part, there isn't enough tension on the tape wraps to case any shifting of the tape but changes in temp. and humidity allows the tape to go into motion. What you end up with are sections of the tape wrap that are loose (allowing tape "pops" ) and others that are very tight. This motion of a stored tape is never linear so sections will stick out of one side or the other allowing curling to tape place. Even the looser winds have some tension and they still want to move to the center of the reel. This results in the outer edge or edges (if it's just a loose winding) to curl toward the hub. Any curling or warp will reduce the tape to head contact and result in a significant loss of signal.

How I do go on! Holy cow, I certainly don't mean to scare folks but once I get on a subject,.. well, I guess the evidence is clear to see!
In any case, set your machine to record with the lowest setting available and be conservative with your recording levels. You'll need to experiment a bit but you can conceivably record on any tape. Personally, after hearing a very early recording a few weeks ago, I'd love to find some 3M 111 to fool around with (Richard Link's Doc Evans tape was recorded on it as heard at Larry Toy's get together).
Regarding CrO2 and metal tapes, I'm not sure of the dates that those were used but it was for use with the slow speeds that are encountered with cassettes. Memorex developed them and I had a few friends who worked there. I never used their products again! (just joking)

Ben, the tapes that were sold under several names; Shamrock, Concertape,  and RadioShack , just to name a few, were B stock from any of the major players at the time (mostly Ampex and 3M). The reason they never include quality info is they never knew what was going to be loaded onto those reels when they printed the boxes.
steve koto
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Offline analogfan

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Re: ampex 406 Sticky-Shed
« Reply #6 on: February 28, 2010, 07:09:01 AM »
A good friend of mine is a musician and has three R2R tapes I am transcribing for him to CD-Rs.  Equipment is an OATRI B3 5050 and an Alesis ML 9600.  The tapes are "one of a kind".

The tapes are Ampex 406 and have sticky-shed.  They were recorded in the 70s and have remained stored since then.

1. How critical is it to unpack them before baking?  I am concerned about unpacking them on my OTARI (fixed guides and of course they will be in contact with the heads through un-packing).

I have a new (about 5 years old) electric Kitchen Aid electric oven with the built in convection baking feature.

2. Can/should I use the convection oven feature?

The oven has digital temperature controls and I also have an external digital thermometer.

Thank you, Analogfan/Bob Edwards