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Offline Homefire
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« Reply #270 on: August 24, 2018, 12:10:27 pm »
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  Welcome to the Forum.  Looking forward to your post.  What type of Metal Detecting do you Enjoy?  What are the Metal Detecting Laws like there in Iran ?  Are you even legally allowed ?  See you have lots to talk about. 

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« Reply #271 on: August 28, 2018, 03:12:53 pm »
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Hi, I finally found almost all the resistance values in 1% but they are 0.25W, does it work with this power without any problems?
Thanks.

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« Reply #272 on: August 29, 2018, 09:02:59 pm »
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Yes  1/4th W should work fine unless the schematic calls for higher power .  The Damping Resistor and other power related resistor would  be asking for more.  1/2 or 1W on some maybe.  Should be indicated on the Schematic I would think.

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« Reply #273 on: August 30, 2018, 01:31:36 am »
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Thank you Homefire, I can not find lf357 and MPSA14, are there equivalents for these. Something else, can I use potentiometers 50K and 500K   
or other values instead of 25K and 250K, thank you

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« Reply #274 on: August 30, 2018, 06:17:04 am »
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Quote:Posted by amitech1982
Thank you Homefire, I can not find lf357 and MPSA14, are there equivalents for these. Something else, can I use potentiometers 50K and 500K  
or other values instead of 25K and 250K, thank you

We have had lengthy discussions about the LF357. The LF means it is very low power, which adds to battery life. Virtually any op amp with the same footprint will work. Stay with a CMOS device if you want to remain low power. Gain in almost any op amp is identical. Purity of signal is also important but the LF357 is operated at very low frequency so any high grade op amp will do the job.

As to the MPSA14, dozens of sellers carry it on eBay. Also, they are available at

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http://www.futurlec.com

They part is a Darlington pair transistor in a single package. High gain, low power with a 1.2 amp current rating. This is important and will limit your choice of a substitute. Nothing less than an Ic (collector current) of 1.2 amps is essential. But, as I said, there are multiple sources.

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« Last Edit: August 30, 2018, 06:18:24 am by GoldDigger1950 »
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« Reply #275 on: August 30, 2018, 09:47:28 am »
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thank you gd, is the lf356 is suitable knowing that its gain is 5 Mhz while the lf357 has 20 Mhz gain.

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« Reply #276 on: August 30, 2018, 11:31:35 am »
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Mhz is a frequency, not a gain, but the frequency we use is much, much lower so as long as the pins are the same, it should work fine.

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« Reply #277 on: August 30, 2018, 01:55:17 pm »
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Thank you GD, I know very well that the Hz is the unit of frequency, but I do not understand why in the datasheets we find the GBW (Gain Bandwith Product) expressed in Mhz.For the lf356, according to the datasheet, is almost identical to his brother lf357, only deference is the GBW.

Posted on: August 30, 2018, 01:48:20 pm
excuse me, something else please, is the galvanometer indispensable? can we replace it with another instrument?

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« Reply #278 on: August 30, 2018, 06:38:44 pm »
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Dear all..
how is the comparison with XR71 ??

Posted on: August 30, 2018, 06:36:14 pm
I mean the comparison of its capabilities ... Boxing

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« Reply #279 on: August 30, 2018, 06:51:59 pm »
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   The main difference between the two circuits is intended use.  The XR-71 is primarily intended for use with a Large Coil 1m x 1m from what I've read. 

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