how about using J111 J175 Jfets in F5

That's Idss I believe is not a drawback.

Papa explains it nicely on the F5T article (page 5)
Although I can't remember if vanilla runs on lower V.

At 8mA they operate close to 200mW
You can get away with a bit above that, but you have to ensure proper ventilation

20mA (will work a bit lower because of the degeneration) will push them close or above max power dissipation levels

So you will probably have to increase the degeneration resistors to tame them
 
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Papa explains it nicely on the F5T article (page 5)
Although I can't remember if vanilla runs on lower V.

At 8mA they operate close to 200mW
You can get away with a bit above that, but you have to ensure proper ventilation

20mA (will work a bit lower because of the degeneration) will push them close or above max power dissipation levels

So you will probably have to increase the degeneration resistors to tame them
will be hardly using in 2.5ma so I believe there is no need of heatsinking on them.
 
Official Court Jester
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xconductance , degeneration , Idss , thus value of drain resistors to open mosfets ..... at least OLG (and control of output gates) is going doooooown

no way Jose ...... plenty of factors to solve successfully , and to have much worse than original

as I sad 50 bucks for LSK is peanuts in overall sum , especially when you count what's price of original FW F5 ........ and we got all what's important ( both brain and ball$ ) for nuttin'

so , too much of cheapskatin' is on verge of disrespect ...... and deeply in foolishness

(said ZM, biggest cheapskate of all Greedy Boyz)
 
Official Court Jester
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I have approx. 500 of each - J309 and J271

even if these are on par with Toshibas (and LSK) with xconductance , I can use them instead of Toshibas only in stages where biasing is via CCS or something , without too much influence of degenerating resistance

in F5 ( and other stages where biasing is made through source impedance ) , Idss is of same importance as xconductance

F5 is soooooo optimized , that any change will result in practically completely different amplifier

doable , possible , even resulting in great amplifier ..... but task not for someone in need to ask simple questions

not mocking or disrespecting anyone , just stating the facts
 
I have approx. 500 of each - J309 and J271

even if these are on par with Toshibas (and LSK) with xconductance , I can use them instead of Toshibas only in stages where biasing is via CCS or something , without too much influence of degenerating resistance

in F5 ( and other stages where biasing is made through source impedance ) , Idss is of same importance as xconductance

F5 is soooooo optimized , that any change will result in practically completely different amplifier

doable , possible , even resulting in great amplifier ..... but task not for someone in need to ask simple questions

not mocking or disrespecting anyone , just stating the facts



[emoji23][emoji23], sometimes situation could be to gift an amp to one of your family member or a friend, because you loan Speakers from them....no way I am parting with my 2SK’s for a gift...want to live with guilt, but not JFET’s
 

PRR

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I see it in more datasheets from JFET's: "Sourced from process 51" .....
What does that mean? What is the manufacturer trying to tell us with that information?

There are 9,876 different JFET part numbers.

There are basically about 13 JFET masks (the Silicon layout).

Some parameter adjustment is possible "in the oven" with dopant concentration and cooking time, but not a lot.

Say you make a lot of cookies. Even using the same spoon, flour, lard, oven setting, they don't all come out identical. Soft, crunchy, plump, flat. Same in JFET processing. Vto and Idss will vary over a wide range. This influences Gm. Leakage and breakdown voltage also vary a lot.

So the JFET maker runs "process 50", and then *sorts* the resulting parts. Parts with "good" parameters are sold under "good" part numbers and should fetch "good" price (in an ideal world). Lesser parts may be plenty fine for some users, if they can pay less. That's how we got so many part-numbers from a limited range of basic Processes.

Processes 50 (51?) is perhaps the most popular. Just a good all-purpose size and parameters. My book is packed away. I recall another with very small size for low-low leakage, one of huge size for low Ron, and a dual (which seems to be obsolete).