Mystery cassette tape

[cmjones01]

A while ago I bought a batch of mixed, used cassettes because it had some interesting tape types in which I wanted to experiment with. One of the cassettes appeared to be a BASF Chrome Maxima II, a type with an excellent reputation which I was looking forward to trying out. But on closer inspection, all was not well. The tape was broken.

I took the cassette apart to repair it and found something odd. The tape inside wasn't BASF chrome at all, but something which was shiny brown on one side and matt black on the other. I discarded the shorter part of the broken tape and reattached the remaining part to the other hub.

The tape plays OK, and contains some rock music recorded at a very high level, but it's definitely short of treble. It's sort of what I'd expect from a ferric tape put in to a chrome shell and thus biased as a chrome tape by a cassette deck.

But what is this tape? It clearly doesn't match the shell, but is it a back-coated ferric type? Did they even exist for cassettes? It reminds me of the tape used in 8-track cartridges with its lubricating coating on the back.

I did wonder if it was ferrichrome tape, but comparing it with an actual Sony FeCr tape the colours are the wrong way round - the FeCr is black on the recording side with the underlying brown ferric coating visible from the rear through the clear base. Maybe it's ferrichrome inside out and I'm just seeing the ferric layer? But that surely wouldn't play properly. The recording that's on there definitely plays the right way round, so it was presumably recorded with the tape in this configuration and not mirrored.

Any ideas? I attach two pictures - one of the mystery tape looped out of the cassette, and the other of a genuine unmolested Sony Ferrichrome tape so you can see what it looks like.

Chris

[TIMTAPE]

The only example I remember noticing of a back coated cassette tape was in a specialised test cassette for use with biasing high speed cassette duplicators. The company was the US Audio Telex but the tape itself was probably made by another US company, maybe Ampex or Scotch..................... ... .... .. I guess manufacturing a back coated cassette tape wouldn't have done any harm but it wouldnt have been as necessary in ensuring an even tape wind or tape 'pack' as with say open reel, as cassettes already used 'slip sheets' to gently guide the tape into a smooth tape pack.. ............. ....
... Back coating can also reduce static discharge 'clicks' which did sometimes occur in cassettes I saw when recorded at high speed in duplicators. I remember particularly a Maxell cassette which did this in an Audio Telex duplicator, but again we never found out what specifically caused the static buildup or discharge. We just changed to another cassette brand an all was well.. .. . ................ .Some open reel tapes used a black oxide and brown seen through the base material. Once I was fooled by this and played such a tape brown side to the head. The muffled playback and especially absence of tape hiss was the giveaway. Flipping it black side to head fixed it.

[paulsherwin]

Given that a pressure pad is part of the CC standard, it seems unlikely that anybody would use back coated tape stock.

[TIMTAPE]

Good point, unless they were used in a Nakamichi with pressure pad lifter. Although even there the tape's back side still unavoidably scrapes against multiple fixed points in the cc shell.

[DrStrangelove]

Originally Posted by TIMTAPE

Some open reel tapes used a black oxide and brown seen through the base material. Once I was fooled by this and played such a tape brown side to the head. The muffled playback and especially absence of tape hiss was the giveaway. Flipping it black side to head fixed it.

Hence the "Record on shiny side" instruction.

I don't recall ever seeing any Scotch audio cassettes with back coating despite all my laborious ferreting about in the returned goods for cassettes to repair and play on afternoon shift.

Used to hate the people who didn't write on the cassette.

Especially after the repair of the Nth iteration of "Band on the ****ing run".

Stone me, that was a while ago, a mere 45 years.

[TIMTAPE]

Originally Posted by DrStrangelove

Hence the "Record on shiny side" instruction...

In that particular case yes. Interestingly with cassettes, the early ones had the usual "dull side to the head". But on later cassettes such as a TDK SA I'm looking at now, both sides of the tape seem equally shiny! So no apparent visual difference but magnetically there is still a difference.

[Mooly]

For some totally obscure reason that totally eludes me and I'm suddenly remembering the unique smell of the Sony FeCr cassettes. Even after all these years I can recall it...

Also seem to remember the Sony tape never looked flat (flat as in geometrically) and had a curve to it when not under tension. Bizarre things to recall I know. BASF Chrome always looked a wider tape no doubt to it being flat.

[cmjones01]

I'm now wondering even more whether the tape is FeCr inside out. Some early chrome tapes did have a distinctly matt appearance. I've got a "Permaton" branded one here which I think is Agfa tape in a cheaper shell, put together in West Berlin when that was a thing. It's pretty matt but sounds perfectly good. I should try recording on the mystery tape both ways round and see what happens.

In the mean time I've found a couple of "Universum" (roughly the German equivalent of Curry's) branded FeCr tapes advertised cheaply locally so I've ordered those to have a look at. They look like they come from the Agfa/Permaton stable too, so I'm curious to see if the tape is matt.

Chris

[ben]

The old Scotch Dynarange cassettes (sometimes in semi transparent blue and orange shells) used a back coated tape, called 'positrack'.

I also have a BASF ferrichrome which is black backed but whose top layer is brown oxide, just like the tape in the OP, so this tape is likely original.

[bluepilot]

I had a cassette deck, an Aiwa ca. 1980 vintage but can't remember the exact model. It had a tape analysis mode. You inserted a tape and it would perform a test recording to determine what sort of tape it was. You could then record with optimized parameters. Maybe you could find a deck with such a feature and it would tell you what sort of tape it is.

[ben]

The Aiwa AD-F770 (and higher models in that series) and Revox B215 both have auto calibration, but good luck finding one at a sensible price!

[cmjones01]

I don't think the tape is original because it's in a "Chrome extra" shell with chrome identification knockouts which a ferrochrome tape wouldn't have. It's also got no leader so it's definitely a bodge job!

I like the idea of exploring the tape's characteristics using a suitable deck. My first choice would be my Sony TC-K81, a 3-head dual-capstan deck which has manual controls for bias and record gain, four different record EQ settings including one specially for FeCr tapes, and built-in calibration oscillators. I find the manual adjustments can give you a great feel for how the tape is behaving. This deck could probably make a competent recording on a roll of toilet paper if only its take up clutch worked properly, which it doesn't, so it's out of action for now. So I'll use the Denon DR-M22 which is currently on duty in the workshop. It's also a 3-head dual-capstan machine and has manually adjustable bias but less flexibility in EQ and record gain. It has auto tape type detection so I'll have to fox it with bits of sellotape on the cassette shell.

I'm looking forward to trying some recordings on the mystery tape, both ways round. If it doesn't work well on the matt black side then it may well be the Scotch Dynarange type, or perhaps FeCr with the layers in the opposite order to what I expected.

Chris

If

[DrStrangelove]

Originally Posted by ben

The old Scotch Dynarange cassettes (sometimes in semi transparent blue and orange shells) used a back coated tape, called 'positrack'.

Interesting. When did that appear?

[cmjones01]

Well, thanks to Ben, I think we have a winner. The tape seems to be a high-quality ferric with some sort of back coating, which makes that Scotch Dynarange a strong possibility.

Recording on the shiny brown side the tape behaves as a premium ferric. Chrome bias is far too much for it, but a bit of tape over the notch in the shell and it's much happier. Output level is 2-3dB higher than the Maxell UR my deck was set up with, but this tape needs a bit less bias than UR to give its best. That's an unusual combination - normally premium ferrics like TDK AD and AR need more bias in order not to sound too bright.

I laboriously turned the tape inside out by winding it backwards with a biro and tried recording on the matt black side. Whatever's on that side it's not magnetic - results were a total disaster with hardly any output at all.

I think it's unlikely that this is a ferrochrome. It doesn't have the bright sound I would expect from a ferrochrome biased as a ferric, and I can't see how a FeCr would end up with a matt black back because the black chrome layer would be visible through the clear tape, which ought to be shiny.

So, back-coated ferric it is, and that Dynarange looks like the strongest candidate.

Thank you, Ben, I think that might be a mystery solved!

Chris

[ben]

I also have some Scotch cassettes from the late 70s with a gold label that I forgot to mention earlier in the thread. These are more likely candidates as the oxide is light brown whereas the older blue dynarange ones I mentioned had a dullish, dark brown oxide.

What has likely happened is that the tape broke - or the splice gave way - and because these Scotch all had welded shells, someone broke it open and retrieved the spools.

[Simondm]

Agfa PEM 368 and 468 uxed to have a black back coating. Those are both 1/4" types. 368 being the thinner base. It looked very similar to your pictures (had printing on it tho, which is helpful for cut editing).

I'm not sure what the purpose of the back coating was, but I wonder if they used the same coating on cassette tape, in which case it's possibly ferric. I've used/owned very few AGFA cassettes, so its only a guess.

[DrStrangelove]

Ben is quite correct.

Having found some decidedly ancient Scotch audio cassettes some are, indeed, back coated.

It even states the fact on the case.

The pressure pad on the back coated tapes is no longer a pristine white or slightly brownish white, but a distinctly dark grey to light black.

However other Scotch tapes of the same vintage aren't back coated, one side being brown and the other being shiny.

I must admit that my increasingly elderly eyes found it difficult to see the back coating since it's remarkably thin and not particularly different in colour from the magnetic layer on at least one of the cassettes.

I found a rather interesting pdf on the manufacture of magnetic tape.

https://sbe.org/handbook/fundamental...netic_Tape.pdf

[TIMTAPE]

Originally Posted by Simondm

Agfa PEM 368 and 468 uxed to have a black back coating. Those are both 1/4" types. 368 being the thinner base. It looked very similar to your pictures (had printing on it tho, which is helpful for cut editing).

I'm not sure what the purpose of the back coating was...

As I understand it the purpose of the essentially carbon based back coat was to:

1. Allow a smoother tape "pack". Compared to the normally smooth surface of the tape's base layer, the rough surface of the back coat allows the air to escape more quickly as the tape winds fast onto the reel, preventing what is analogous to a car tyre "aquaplaning" on a wet road. The tape doesnt slip and slide sideways as much but grips the previous wind better resulting in a smoother tape wind at higher wind speed, which is especially safer for long term tape storage and transporting.

2. Prevent or reduce static electricity buildup.

3?

There have been ongoing discussions as to whether the back coating itself contributed to the "Sticky Shed' syndrome on many tapes made after about 1970 but it's been established that there were tapes manufactured without a back coating which still suffer from SSS.

[Simondm]

Originally Posted by TIMTAPE

As I understand it the purpose of the essentially carbon based back coat was to:

1. Allow a smoother tape "pack". Compared to the normally smooth surface of the tape's base layer, the rough surface of the back coat allows the air to escape more quickly as the tape winds fast onto the reel, preventing what is analogous to a car tyre "aquaplaning" on a wet road. The tape doesnt slip and slide sideways as much but grips the previous wind better resulting in a smoother tape wind at higher wind speed, which is especially safer for long term tape storage and transporting.

2. Prevent or reduce static electricity buildup.

There have been ongoing discussions as to whether the back coating itself contributed to the "Sticky Shed' syndrome on many tapes made after about 1970 but it's been established that there were tapes manufactured without a back coating which still suffer from SSS.

Those make sense, and some brands of cassette had carbon-coated sheets above and below the tape pack(s), to reduce friction and improve the wind.

I can see you'd get static buildup on 1/4", but 1 7/8" ips (normal cassette use) is very slow for that to cause a significant problem. So I guess the coating of the cassette in question, it was most likely to be for improving the wind/pack. Cassettes are pretty vulnerable to edge damage and stretching, and the tiny track width and slow speed really don't help.

Thankfully we never used Ampex during my audio career, however there was a faulty batch of red leader tape, circa 1982, that caused some tape machines to grind to a halt when it went around small diameter tape guides. I think it caused problems for Broadcasting House particularly, as they had a lot of Telefunken machines, which we never did in Bristol. I hardly used them, but I vaguely remember at least one narrow guide/tension detector in the Telefunken path.

I did once have some archival recordings disintegrate on me whilst being transferred. That was ancient "Scotch" tape (i.e. probably 3M) from the 1950s or 1960s. Longitudinal splits started appearing about 1/2" to 3/4" long, which rapidly became big flakes of the stock (including the base). We couldn't salvage it completely.

I think it was cellulose base though, not Mylar, and had been through a rough life (IIRC they were location recordings of Amazonian wildlife). The machine I was using at the time though was a David Lane Nagra (with the outriggers fitted for NAB spools), and they were extremely gentle, and spooled pretty slowly, and as I'm sure you know, there are not really any sharp corners in the Nagra tape path.

[DrStrangelove]

If it's "Scotch" tape it's definitely 3M until 1997.

There was also "Irish" recording tape but I don't know who made that.

Oh: https://commons.wikimedia.org/wiki/F...264546464).jpg

Irish brand magnetic tape was produced by Orradio Industries Inc. in the US.

In 1959 the company merged to Ampex.

Who'd have thunk?