Cubie - small F5 variant with GR grade JFETs and LatFETs

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G

gaborbela

Member
Joined 2005
juma said:
Center taped is usually made by internally connecting two separate windings. You can break that connection and you'll have two separate secondaries.
Or. make the cap. mult. with P-ch MOSFET for the negative rail so the GND goes uninterrupted from center tap.
Click to expand...

Thank you juma
I did checked the transformer (it is inside in old project) and yes I can separate the center tap wire.
There is two wire inside that tubing.
So happy :cheers:, now I can go on and collect some of the missing parts.
I do have all the mosfets including the J-fets.
Those are the hard to find parts.
Greetings Gabor
 
M

marconi118

Member
Joined 2008
juma said:
Measure them and calculate. Think like this:
Click to expand...

understood the schema, my difficulty is to calculate, or find the value per measurement of R1 and R2

in the "standard" F5 EUVL uses one J74 with idss 0,8mA more than the K170 and adds R1 of 5ohm to degenerate the J74 to have the same gm as the K170

This is because the J74 (even with matched Idss) is not a true complementary of the K170. the trick of EUVL is to add degeneration to the J47 to match the characteristic of the 170


In my case with 2x K74GR, should I still use 0.8mA more total Idss than the K170 and 5ohm for R1 and R2?

paralleling fets does increase the gm of the resulting fet?
 
juma

juma

Member
Joined 2005
How do you expect someone to give you a solution on a silver platter if you don't supply the basic data about the JFETs that you got ?
Use the search button, read Borbely's JFET articles, measure your JFETs - asking already answered questions over and over again won't take you very far...
 
juma

juma

Member
Joined 2005
I told you already (post #75) and you didn't read it. And how will that single piece of data help you when it's obvious that you lack basic knowledge on JFETs. And not being able to find Borbely's papers on JFETs tells me that you didn't even try...
So AFAIC, you are on your own, I give up ....
 
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marsupialx

marsupialx

Member
Joined 2004
Getting ready to build! :p
 

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marsupialx

marsupialx

Member
Joined 2004
Thank you!!! I have an even smoother version now. I had not printed it out actual size. If 25mmX65mm is correct, this thing is tiny!!!!! Man, drilling it will be some precision work. Bought a 4x6" piece of fr4 on Ebay. I can screw this up repeatedly and not run out of board. Lats are on order. I have the jfets. WhooHoo!!! This is fun. Thanks, Juma!
 
G

gaborbela

Member
Joined 2005
Be careful you have 2PC of Pc board together!
You have to dived into two piece so you writing in wrong place also you have to mirror imaged.
My lay out for these fantastic little amp!
Only post that so you can see :)
It need to be resized at print out.

Greetings
 

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marsupialx

marsupialx

Member
Joined 2004
Both channels are identical, one is rotated 180degrees from the other. I plan to build it so the lats stick out from each side. As I posted, I am not intending to divide the board. The layout is per juma's post, which says it is copper side view. So no mirroring should be necessary, unless I do a laser print transfer. I could easily arrange them side by side, so the lats would be in a row. Now that I realize how small this is, I may decide to do that. Nice layout!
 
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