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Building a symmetrical psu B1 buffer
Building a symmetrical psu B1 buffer
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Old 10th February 2012, 10:46 AM   #2411
KatieandDad is offline KatieandDad  United Kingdom
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I've just bought a batch of 2SK170BLs (16 of them) for Igs matching.

I am somewhat confused that six of them have Igs = 7mA (ish) and the remainder are 2mA (ish).

Is this normal ?

I can accurately match pairs with Igs around 2.22mA.

This is tested at 10V with G and S shorted.
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Old 10th February 2012, 10:58 AM   #2412
AndrewT is offline AndrewT  Scotland
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Idss is the current that passes when Vgs is zero (i.e. G & S shorted together) when Vds = 10V and Tj = 25degC.

A 9volt battery and room temperature is acceptable for first batching.

Use a 1r0 1% resistor as your current measuring device.
Apply 9V to 1r0+jFET
Measure the mV drop across the resistor. That is your approximate Idss.
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Old 10th February 2012, 11:15 AM   #2413
KatieandDad is offline KatieandDad  United Kingdom
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That's what I did, except that the 1R0 was the internal resistance of the meter on mA range.

I'll try again with 1R0 and measure as you have suggested.
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Old 10th February 2012, 11:22 AM   #2414
KatieandDad is offline KatieandDad  United Kingdom
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The results are exactly the same..??
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Old 10th February 2012, 11:31 AM   #2415
Salas is online now Salas  Greece
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Building a symmetrical psu B1 buffer
Possibly fakes. They should all fall in the BL IDSS range, else very suspect parts.
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Old 10th February 2012, 11:42 AM   #2416
KatieandDad is offline KatieandDad  United Kingdom
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To others. Just beware - these came from www.dalbani.co.uk .

I will be phoning them shortly to see what they propose to do about the fakes.
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Old 10th February 2012, 11:46 AM   #2417
buzzforb is offline buzzforb  United States
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Neve done business with them but dabani supposedly has a good reputation, but those do sound fake. I have a 100 coming from a certified source. I will send you some at cost if you are willing to wait and pay shipping to the UK.
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Old 10th February 2012, 11:56 AM   #2418
KatieandDad is offline KatieandDad  United Kingdom
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Buzzfoorb.

I'll take you up on that offer please.
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Old 10th February 2012, 11:57 AM   #2419
wintermute is offline wintermute  Australia
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Building a symmetrical psu B1 buffer
I bought a batch of 100 from spencer and they ranged from about 6.5 t0 11. 2.2 is definitely very suspect.

Andrew, when did you start using 1R0? Isn't that a tad low? I used a 0.1% 100 ohm resistor and that seems to work quite nicely. Perhaps 100 ohms doesn't give quite enough resolution though for really close matching, a 10 ohm resistor would allow me to use the 200mV range on the multimeter rather than the 2V range... I assume this is the reason for going with such a low resistor value? Or is it because you can just use the reading without needing to divide by the resistance?

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Last edited by wintermute; 10th February 2012 at 11:58 AM. Reason: removed dumb comment ;)
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Old 10th February 2012, 12:00 PM   #2420
buzzforb is offline buzzforb  United States
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Quote:
Originally Posted by KatieandDad View Post
Buzzfoorb.

I'll take you up on that offer please.
I'll let you know when I get them.
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