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Author Topic: Technics RS-1500 Record Gap Length Q  (Read 5386 times)

Offline xcortes

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Technics RS-1500 Record Gap Length Q
« on: September 08, 2010, 08:33:46 AM »
I'm in the process of learning to rebias a machine for different types of tape. In this case a Technics RS-1520 with TdP electronics.

I think I basically understand how to do it. The problem is that the dB over @ 10khz specified for each tape varies with the record gap length (in a range usually going from 0.25 to 1.0 mils).

My question is: what is the record gap length for the Technics RS 15xx series?

Thanks,

Xavier

http://www.rmgi-usa.com/page3/assets/BiasChart.pdf
Xavier Cortes

Offline Tim

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Re: Technics RS-1500 Record Gap Length Q
« Reply #1 on: September 08, 2010, 10:50:03 AM »
My guess is .25 mils which would mean 3 to 4 db overbias at 10KHz depending on which tape you use.   This is for 15ips record.

JRF or Flux Magnetics may know the exact measurement for that particular head.
Tim Leinbaugh
Service Technician
with RTR specialty.

Offline xcortes

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Re: Technics RS-1500 Record Gap Length Q
« Reply #2 on: September 10, 2010, 05:32:13 PM »
The only information I've found is that on the Nortronics guide:

http://www.magneticheadcompany.com/NORTRONICS_GUIDE.pdf

The record head for the Technics RS1500 is specified as 9203. And the specs for 9203 show a Gap Spacer distance of 500 u I n. So if gap spacer is the same as gap length and mil is 1,000 u I n the answer is 500 mils.

I hope someone can help me confirm.

Thanks!
Xavier Cortes

Offline High and Outside

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Re: Technics RS-1500 Record Gap Length Q
« Reply #3 on: September 10, 2010, 08:56:00 PM »
I've got some help for you, even though I don't know the gap length of that head.

There is an alternative method of setting the bias that doesn't depend on the gap length. Just use 1KHz, and overbias by a quarter of a dB. Or two tenths of a dB if you're really picky. This works with any tape, either 7.5 or 15 IPS, and any head gap.

This is just as accurate as using 10KHz when you know the gap length, and much more accurate than using 10KHz when you don't know the gap length.

You can see a nice discussion of this in the MRL publication "Choosing and Using MRL Calibration Tapes" paragraph 7.1.
Paul Stubblebine
Managing Director, The TapeProject

Offline xcortes

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Re: Technics RS-1500 Record Gap Length Q
« Reply #4 on: September 10, 2010, 10:14:28 PM »
thanks Paul!
Xavier Cortes

Offline Tim

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Re: Technics RS-1500 Record Gap Length Q
« Reply #5 on: September 11, 2010, 01:03:43 AM »
After setting the bias for .20 db, 1KHz over-bias, switch your generator over to 10KHz and note the level.  Then start reducing the bias and see how many db the 10K level goes up until you reach the peak.   The db amount between the peak and the original level would be your equivalent 10k over-bias amount.  Might be in the 3 to 4 db range.  I find it easier to dial in the bias using the 10K tone only because 3 db (for example) is easier to see on a meter than .20 db.     
Tim Leinbaugh
Service Technician
with RTR specialty.