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Old 26th March 2013, 03:51 PM   #741
AndrewT is offline AndrewT  Scotland
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quite a number of the jFETs in a DCB1 and in many of the Salas style shunt regulators do not need to be high gm, low pinch off voltage types.
Many of the very cheap and very available lower gm with higher pinch off are very suitable.

Some of the Salas regulators have a Vbe across the jFET. This one jFET must be a low pinch off type.

I have used bf244 a & b grades and have posted details in many replies/advices.
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Old 26th March 2013, 04:21 PM   #742
Salas is offline Salas  Greece
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They always need be low noise enough parts nonetheless so to make comparable builds.
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Old 27th March 2013, 03:53 PM   #743
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Quote:
Originally Posted by AndrewT View Post
quite a number of the jFETs in a DCB1 and in many of the Salas style shunt regulators do not need to be high gm, low pinch off voltage types.
Many of the very cheap and very available lower gm with higher pinch off are very suitable.

Some of the Salas regulators have a Vbe across the jFET. This one jFET must be a low pinch off type.

I have used bf244 a & b grades and have posted details in many replies/advices.
I can recall that I have read some of your replies somewhere before.
Yet, I need some time to find them out.

Anyway, your information is very useful.
I look up several datasheets this morning and I found that BF245B seems to be a good alternative to 2SK170BL. It has very low noise figure and low input capacitance.

Also, 2N5457 has similar specification except that its Idss is widely spread, i.e. 1mA ~ 5mA. For 2N5458, Idss range from 2mA ~ 9mA. It may be used for the SSLV where strict matching of Idss is not crucial. It is really dirt cheap!
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Old 27th March 2013, 03:57 PM   #744
Salas is offline Salas  Greece
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If you will end up to some candidates let me know before you build so to check the phase margin of the total circuit.
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Old 14th April 2013, 12:27 AM   #745
kop89 is offline kop89  United States
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Which four of the 2SK170 has to be matched? Are these the ones near the output relay at the center of the PCB?
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Old 14th April 2013, 12:47 AM   #746
Salas is offline Salas  Greece
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Yes the 4 in a row ones.
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Old 16th April 2013, 06:48 AM   #747
kop89 is offline kop89  United States
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Just want to make sure I understand this correctly. So the LED must be matched so that the sum of the voltage drop of each group is the same?

So I will group the LEDs as follow (measurement in Volts):

For the 3 LED rows:
Group 1A: 1.947+1.947+1.949 = 5.843
Group 1B: 1.947+1.948+1.947 = 5.843

For the 5 LED rows:
Group 2A: 1.952+1.955+1.956+1.957+1.959 = 9.779
Group 2B: 1.952+1.955+1.956+1.957+1.959 = 9.779

Do I group this correctly?

Thank you!
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Old 16th April 2013, 06:57 AM   #748
Salas is offline Salas  Greece
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Yes, but do you have options for settling 2A,B lower near 9.4V? That would be nearer 10V when 0.6Vbe is added from the BJTs. Not that is anything too important subjectively.
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Old 16th April 2013, 07:20 AM   #749
kop89 is offline kop89  United States
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Yes, but do you have options for settling 2A,B lower near 9.4V? That would be nearer 10V when 0.6Vbe is added from the BJTs. Not that is anything too important subjectively.
I guess not, I hope this would not be a problem.
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Old 16th April 2013, 05:27 PM   #750
Salas is offline Salas  Greece
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Not a problem. Small difference. Sits only at +4% the voltage it was "voiced" originally.
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