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Old 9th January 2016, 12:07 PM   #6011
jwilhelm is offline jwilhelm  Canada
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Quote:
Originally Posted by AndrewT View Post
A jFET on it's own is not an amplifier.

The jFET must be built into an amplifier circuit.
The circuit provides the input signal route.
Meaning they are either on or off like a relay?
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Old 9th January 2016, 12:14 PM   #6012
still4given is offline still4given  United States
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I have this meter. LCD Transistor Tester Diode Triode Capacitance ESR Meter mos PNP NPN LCR SZTM | eBay

It actually does a surprisingly good job at most things but jfet fool it. It will always find the gate but can't determine the source from the drain. I have also read that they can be inverted, though here some have indicated that in this circuit that may not be the case. I had thought to try inverting them just to see. I don't remember where I got these. I bought them for an older project. IIRC they worked fine.

The center pin is the gate so inverting them should be easy. Maybe I'll give that a try today just for kicks.
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Old 9th January 2016, 12:18 PM   #6013
AndrewT is offline AndrewT  Scotland
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Turn it over and read the number on the big chip. Does it say ATmega 328?

Now try measuring a jFET.
Swap it around the various holes in the zero insertion force device holder.
It should consistently tell you it is a jFET and it should consistently identify the gate lead, even though you have moved it from 1 to 2 to 3.

Quote:
It actually does a surprisingly good job
I don't agree.
I reported some months ago.
It consistently tells me that dozens of different BJT devices have the same hFE and the same Vbe.
Yet, when I test them manually, noting Ib & Ie I can see that hFE is different, sometimes by an enormous amount. In hFE respect it is worse than the DMM hFE test.
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Last edited by AndrewT; 9th January 2016 at 12:24 PM.
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Old 9th January 2016, 12:43 PM   #6014
still4given is offline still4given  United States
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Quote:
Originally Posted by AndrewT View Post
Turn it over and read the number on the big chip. Does it say ATmega 328?

Now try measuring a jFET.
Swap it around the various holes in the zero insertion force device holder.
It should consistently tell you it is a jFET and it should consistently identify the gate lead, even though you have moved it from 1 to 2 to 3.

I don't agree.
I reported some months ago.
It consistently tells me that dozens of different BJT devices have the same hFE and the same Vbe.
Yet, when I test them manually, noting Ib & Ie I can see that hFE is different, sometimes by an enormous amount. In hFE respect it is worse than the DMM hFE test.
As I said, it does a good job at most things. I find it agrees with my DMM fairly close I was surprised at how well it matched mosfets. I had a box full of irfp's that I had matched using a jig and it matched up with the numbers I had gotten to a tee. I was pleasantly surprised.

I have found reading hfe to be tricky anyway because temperature of the device changes it so drastically. I have often wondered how oem manufactures deal with that when they are building so many units. I wonder how close a tolerance they work with.
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Old 9th January 2016, 12:51 PM   #6015
AndrewT is offline AndrewT  Scotland
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Originally Posted by still4given View Post
....................
I have found reading hfe to be tricky anyway because temperature of the device changes it so drastically. I have often wondered how oem manufactures deal with that when they are building so many units. I wonder how close a tolerance they work with.
They either buy in duals and charge the customer for the priviledge , or they don't design for needing close matching.
Very few actually match themselves, but some will match. A tweak of a pot on the testing line is about as close as they get.
Speaker manufacturers went over to computerised measuring & matching many decades ago. I suppose some could be doing similar with semiconductors.
IC are now laser trimmed to meet guaranteed performance targets. That is a form of matching. Resistors too.
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Old 9th January 2016, 02:48 PM   #6016
jwilhelm is offline jwilhelm  Canada
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Quote:
Originally Posted by AndrewT View Post
They either buy in duals and charge the customer for the priviledge , or they don't design for needing close matching.
Very few actually match themselves, but some will match. A tweak of a pot on the testing line is about as close as they get.
Speaker manufacturers went over to computerised measuring & matching many decades ago. I suppose some could be doing similar with semiconductors.
IC are now laser trimmed to meet guaranteed performance targets. That is a form of matching. Resistors too.
I think the problem with these Ebay devices and most voltmeters is they only test at one preselected current flow. I'd like to design one that will test at a selected current that will match what is used in circuit.
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Old 10th January 2016, 08:03 AM   #6017
adamart is offline adamart  Philippines
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shalom... apex audio do you have a pcb in this nx16 NMOS amp? i like this design and is it possible to use your 555 speaker protect with this circuit? instead?
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Old 10th January 2016, 08:31 AM   #6018
gaborbela is offline gaborbela  Canada
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Originally Posted by abetir View Post
I made a quick sim of A Class PSU to find out if the SK devices will work.
I used SK117, a low noise jfet counterpart for SK246 (no model available in Multisim lib). All 2N devices for the small TO-92s and TIPs for the output regulator. It seemed to work without a problem, trimmer adjust is set to 80%.
At 100% it is outputting 32vdc.

Terry, perhaps one or two of the SK device is failing, have you tried replacing them with newer ones?
Can we use BF244 instead BF245 they are very similar.
3 X BF244A N Channel RF Amplifier Transistor Free Shipping | eBay
Very likely if has the same pin out..
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Old 10th January 2016, 09:42 AM   #6019
AndrewT is offline AndrewT  Scotland
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Pin out of my BF244 and BF245 are different, even though they are the same manufacturer !!!!

a, b & c are the Idss grades.
All are low gm, high pinch off voltage and make good cascodes for 2sk170.
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Old 10th January 2016, 11:07 AM   #6020
rohin is offline rohin  India
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Originally Posted by us1070 View Post
So i am thinking to skiping the Good Apex A Class PSU as it requires my time. So will this replacement work insted
LM317 LM337 Adjustable Filtering Power Supply AC/DC Voltage Regulator PSU DIY Kit-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

or You can suggest me any PSU in Aliexpress under $30

Its for my 2 x ML3 pre amp
use this psu for ml3 and see the quality difference .this is working 100% and very good.use bf 245 .
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