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F5 Turbo Builders Thread
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Old 18th May 2018, 09:12 AM   #5161
Zen Mod is offline Zen Mod  Serbia
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F5 Turbo Builders Thread
https://www.google.com/url?sa=t&rct=...c-aLusOnIe5hq2
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Old 18th May 2018, 10:34 AM   #5162
dewdrop is offline dewdrop  Singapore
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Awesome ZM! Thanks.
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Old 18th May 2018, 11:40 AM   #5163
dewdrop is offline dewdrop  Singapore
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Another question: for rail voltage, do I need to measure the actual under load?
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Old 18th May 2018, 01:00 PM   #5164
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is there different way ?

measuring unloaded PSU is step , confirmation that everything is OK
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Old 19th May 2018, 02:25 AM   #5165
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Roger ZM.
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Old 27th May 2018, 08:29 PM   #5166
MrBoat is offline MrBoat  United States
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Is it completely necessary to match JFETS? I have parts to build this amp and others (not that I am going to anytime soon), gifted to me by a former EE/hobbyist but they are not all matched pairs. I have 3-4 pairs of matched 2sk170 but others like 2SJ74 are just a random group of a dozen or so.
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Old 27th May 2018, 08:41 PM   #5167
Zen Mod is offline Zen Mod  Serbia
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easy to test them for Idss

play safe
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Old 27th May 2018, 10:55 PM   #5168
Dennis Hui is offline Dennis Hui  Canada
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Mr Boat,

Definitely measure Idss of your parts since the spread for random parts is quite large. For measurement, please see setup here:

Transistor matching

If you don't have a meeting that can give you mA reading, consider replacing ammeter with 100 ohm resistor and measure voltage drop and infer current from that.

Dennis
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Old 28th May 2018, 12:33 AM   #5169
6L6 is offline 6L6  United States
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F5 Turbo Builders Thread
SenorBarco,

The way the F5(t) works and is designed, you don't need to match the Jfets, but everything further down the chain falls into place if you do match them, or at least get them as close as you can.

Considering measuring for Idss takes merely a 9v battery and your meter, I agree with ZenMod's advice to play safe and match them as close as you can, it will pay dividends later when you bias it.


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Old 28th May 2018, 06:02 PM   #5170
MrBoat is offline MrBoat  United States
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Quote:
Originally Posted by Dennis Hui View Post
If you don't have a meeting that can give you mA reading, consider replacing ammeter with 100 ohm resistor and measure voltage drop and infer current from that.

Dennis

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