How to tell if tape heads are good?

blhagstrom

Mad Scientist, fixer.
Subscriber
I get a lot of tape decks to flip.
People ask for photos of the heads.
All heads look OK to me.
I can understand commercial decks that may have passed millions of miles of tape and may show track wearing, but consumer heads?

What are they looking for?

Any photos of "bad" heads out here?
 
Looking closely at a junker I have here.

I see under a good light after a good alcohol cleaning that they look rough in the tape contact.
Now I see wear on a guide pin.

I think these are shot. Or at least unusable as is. I've heard of re-lapping but that's a bit advanced as a selling point.
Just another heavy piece of junk.
 
As much as I hear about the smoothness of heads, I also hear about the "dreaded opening of the gap". What causes the gap to open?
Thanks
 
This website has much information that may help you to understand this term.

http://www.jrfmagnetics.com/

The section on head reconditioning includes a cross-sectional drawing of a typical tape head. A open gap condition is reached when wear of the tape head reaches the point where the gap spacer is no longer held between the two poles of the head.
 
Some consumer decks got heavy use in the day. Some head materials were not as hard as others, so significant wear is often found. Akai "glass" heads were very durable, but sometimes failed in their own unique way. Even some cassette decks suffered from excessive head wear-mostly earlier models (say, mid 70's). The slow tape speed was a plus in their case, as wear is a function of head hardness and total tape length traveling across the heads. Some tape formulations are reported as being more wearing of heads, although I have never seen an actual set of test data to support this claim.

The JRF magnetics link does an excellent job teaching one about heads, wear, etc., etc.
 
I found a high end Teak RtoR in a local GW about a year ago. it looked fantastic but the heads had a huge groove worn in them, deepest I have ever seen. It looked like a gorge! Such a shame.
 
Sonically: when the midrange response starts to sound as if it's "overtaking" the rest of the frequency range; or if there's little sense of natural treble brilliance (unless you find you have to boost the tone control way past null and then just start getting A LOT OF HISS).
Visually: the worst case is when the gap becomes revealed as a thin, black line vertically down the center. If there's just a flat spot (and no line of the gap opening up) on the head (mainly the PB one): there's a good chance it can be resurfaced with 800-1000 grit sandpaper and polished with automotive wheel polish back to half as much (of original) life expectancy.
 
When I worked for CBS Records and Tapes we used a reel of 3m green lapping tape between quarterly relappings. Quarterly we used a lapping wheel and diamond compound. A fixture on the lapping wheel held the heads and would rock them back and forth allowing lapping of the entire recording surface. I've looked online for the green 3m lapping tape, but see only patches and squares. Anyone know where I can get a 1/4" reel of 3m lapping tape?
 
I recently acquired an RT-707 (for $0.00!) and the heads look like they are in need of some attention. But what I have noticed in my attempts to research this is that there seems to be a shortage of good photos of consumer deck heads- you can find lots of information about the big commercial machines, but not so much on your basic home deck- I really would like to see some clear pictures of heads in various states of wear.....
 
Run your fingernail across the head. If you can feel a ridge, the heads are worn.

That assumes that you have a nail, your sensitive enough to tell and can get you finger into the spot to do this. Highly doubt that’s was mfgrs had in mind.
 
I'd do the playback thing like with LPs, but first clean everything that moves (capstans, guides,
rollers) and where the tape goes over. then demag and then do a listen test.

I used to buy "broken" naks and replace idler wheels, clean (as above) and demag them
and give them away as intros to music - far easier than turntables and music - on cassettes
is far cheaper.

nowadays those 10-20 dollar low-end Naks are now flipped for 80-100,
dirty and needs its first head demagnetization since it was built in the 80s
and 90s.

an Audio Technica auto demag is the best way to go.
 
In the interest of continuing education :rolleyes: here is a photo of the head on the 707 I have acquired. You can see the "fingernail " ridge at the bottom, as Kevin suggested as a test. This unit apparently spent some time in a rather uncontrolled environment. This really isn't even a "before" picture- I had already tried cleaning it a number of times with alcohol and various solvents.

headcu.jpg
 
They should look like this (a 1976 Dokorder 1120 I just finished completely rebuilding since this past April; after getting it for $25):
vZG51f.jpg
 
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