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Gyrator loaded Son of ZV9/F3
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Old 29th August 2018, 09:42 AM   #211
maouna is offline maouna  Greece
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I have already made a pcb for the previous schematic so i would like to give it a try but i dont have the specified part ,only BF245B!!!why you wouldnt recommend it??
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Old 29th August 2018, 11:24 AM   #212
juma is offline juma  Serbia
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Because the other one is better. The one from post #209 will work OK - use those BF245B that you have (Idss=8.8mA) without source resistor (R8,R17) or a very small one (10R) and adjust the value of R3,R21 so that you get half of the regulated power supply voltage at the MOSFET's drains (Q2,Q3).
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Old 22nd February 2019, 12:33 PM   #213
maouna is offline maouna  Greece
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I am almost done with the preamp of post #1 but i have question.
I see a resistor on the mini PCB on which BF862 is soldered.Does this resistor connects to the gate of BF862?
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Old 22nd February 2019, 01:06 PM   #214
maouna is offline maouna  Greece
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For the psu section i am going to use a shunt psu posted by Juma, with 24Vac transformer (35V after rectification). the current source fet bf862 has to be changed to something with higher Vds than 35V.What do you suggest? I have 2SK170,BS170.
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Old 22nd February 2019, 02:45 PM   #215
vdi_nenna is offline vdi_nenna  United States
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Gyrator loaded Son of ZV9/F3
Is the BF861B a suitable replacement for the BF862? What about any of these other jfets at Mouser?

JFET N-Channel SMD/SMT RF JFET Transistors | Mouser

What's the ideal jfet Idss for the circuit in post #1?

I would like to build it like the original circuit.
Are there any changes to the circuit in post #1?

I want to drive an F4 and MoFo power followers.

Thanks,

Vince
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Old 22nd February 2019, 02:53 PM   #216
vdi_nenna is offline vdi_nenna  United States
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Is Idss of 14 ideal?
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Old 23rd February 2019, 04:08 PM   #217
juma is offline juma  Serbia
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Quote:
Originally Posted by maouna View Post
...Does this resistor connects to the gate of BF862?
It's a gate stopper. It doesn't make a difference here because R3 (22k) does that job already.

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Originally Posted by maouna View Post
...bf862 has to be changed to something with higher Vds than 35V.What do you suggest? I have 2SK170,BS170.
2sk170 or 2sk246 (any grade will do).

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Originally Posted by vdi_nenna View Post
Is the BF861B a suitable replacement for the BF862?
BF861B with Idss >= 12mA will do OK.


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Originally Posted by vdi_nenna View Post
What about any of these other jfets at Mouser?
Got no time to browse through all those datasheets but you should look for parts with high gm and linear transfer curve. Although, with some effort, many will work OK.

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What's the ideal jfet Idss for the circuit in post #1?
12-15mA

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Are there any changes to the circuit in post #1?
I don't remember - did many different stuff since then. Maybe you should search/browse through thread(s).

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Is Idss of 14 ideal?
12-15mA
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Old 23rd February 2019, 05:29 PM   #218
vdi_nenna is offline vdi_nenna  United States
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Thank Juma.
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Old 23rd February 2019, 06:08 PM   #219
maouna is offline maouna  Greece
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Thanks for the suggestions.Juma,do you have any other shunt PSU like the one with TL431 but with 48V output and the same noise suppression results??.My load current will be max 22mA
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Old 23rd February 2019, 07:02 PM   #220
maouna is offline maouna  Greece
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If i want to put a coupling capacitor between input volume pot and R3,where should i connect the + of the 10u electrolytic capacitor?(i only have 10uF/50V electrolytic nichicon FW series)

Regarding the 470ohm gate stopper resistor,should i ommit it ithis case? i have already made space for the resistor in my small pcb.
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