Erase head question

F

Findlay

Member
I was a bit surprised a while ago looking at the erase head of my Tascam 244 - it seems the track layout is staggered and not in-line. I wondered why this is? I remember seeing that bias currents for some erase heads can be as high as 70 mA and working voltages as high as 20V or so. This would mean something like a Watt or more being dissipated for each channel. Is this heating effect the reason for the staggered design and is it common in multitrack machines? I'm surprised with this much power it doesn't lead to heating up of the tape when set on pause!
 
Stereo erase heads are often inline but with multitrack ones they are usually staggered. I seem to recall that the erase head on my MSR-24 is NOT staggered, which surprised me at the time.
I'd have to check that when I get home. And yes, I suspect it's to do with the heat dissipation. That's just a guess, though. It might also be to prevent the fields interacting somehow, the erase field most likely being the strongest.
 
The original erase headstacks on the 24-track Ampex MM-1000 weren't staggered. That was in the very early days of 2" 24-track. They had problems with them cracking due to the heat...later versions were staggered. Crazy stuff.
 
Is the current to the erase head cut in pause mode in most decks? Otherwise there would surely be tape damage?
 
Regarding the Telefunken erase head, that is how some manufacturers handled it, especially early on...the staggering. It's the same as IRIG data recorder record/play heads. Actually it's the same idea as the Tascam cassette 8-track record/play head.
 
I don't know the answer to that. And as to other question about pause mode...I guess I don't know that either. You'd have to look at the schematics to be sure. My hunch is that the answer is "yes", the current to the erase head is cut during pause mode. You could always measure the output of your bias amp in rec/play and then see what happens when you pause for your particular machine.
 
Thanks Sweetbeats. I'll try to measure up those values next time I open up. Not that it helps much, but I remember working on a late 70's JVC cassette deck a few months back and noting how rudimentary the pause control seemed - there didn't seem to be any electrical switching just a mechanical link to move the pinch roller. I never dreamed that a long time on pause could possibly cause a "hot" spot on the tape but maybe it could have....
 
I wouldn't think so on a cassette. The flux level necessary to erase Philips cassette tape operating level is a lot different than open reel +6 tape (for example).
 
erase head allignment

As for open reel formats my Ampex 440 1/2 inch 4 channel the erase tracks are aligned. My Tascam 80-8 1/2" 8 channel erase tracks are aligned.
Knowing how manufacturers operate i would guess it has more to do with cost than any other consideration.
don ward audio
 
Less of a need to stagger on a wide format machine like the AG-440-4, and later iterations of the Teac 1/2" 8-track headblock (i.e. 38, 48, 58, TSR-8 and ATR60-8) all used a staggered erase headstack.
 
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