F5 power amplifier

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#1,581
2SJ74 and J108 will be discontinued?

I had heard the infomation on a Japanese blog that 2SJ74 will be discontinued .
It means ,J108 ,almost same with J74,will be also discontinued .

Then,I saw the website of Toshiba-semiconductor and serch J74 and J108.
But any results was not found...:bawling:

They may be a lot of stocks over the world ,
but you should buy them before sold out.

While ,what will be the replacement of them ?J103 and K246?or J104 and K364?
We have only few coices left.
It will be disscuss on Japanese web too.
 
#1,583
unfortunately, i think the big picture that we don't see is Toshiba really doesn't make much profit on those jfets, especially considering the numbers of other devices like memories, mosfets (for switching supplies), microcontrollers, etc. their bean counters prefer to sell. discrete semiconductor sales to high performance audio manufacturers is insignificantly buried under the noise

too bad some of the other premium jfet manufacturers haven't got high performance p channel devices.

allegedly, they're working on it. but the word is don't hold your breath ...
not to mention all our screaming at the high prices if/when they do.

:bawling:

mlloyd1
 
#1,584
Jfet Matching

I have my boards nearly populated and eveything wlse ready to go. As far as I can tell matching the P to N mosfets isnt so critical. Is the JFet matching critical ? I am unsure of how to test them for idss ( I have searched alot for a diagram of a circuit ) Im just chuffed to bits that my first homemade pcb worked and Im on a roll !

dave
 
#1,591
Nelson Pass said:


Matching P to N channel devices is not practical, but using the same
selection codes (BL, GR, V) is desirable.

I don't match P to N devices, just like types.
Click to expand...


Thats the general idea I was getting , as it dosent mention matching in the F5 article. Looks like imight be powering up a channel later today then !
cheers
dave
 
#1,594
jackinnj said:
Erno Borbely also has a pair of articles archived on his site -- which includes a JFET tester circuit.

http://www.borbelyaudio.com/adobe/ae599bor.pdf

and

http://www.borbelyaudio.com/adobe/ae699bor.pdf

Somewhere in this mess of an office I have a USB Based JFET analyzer based on the Measurement Computing data acquisition card -- it's written in VB.net
Click to expand...


You got my interest, I have measurement computing DAC's
laying all over the place. I also have .net.
Tell me more please.
 
#1,595
got my F5 fired up today--1amp fuse, used variac, got to 115v,checked rail voltages +- 26volts-all looked good-turned the pots alternating- 1/2 turn at a time went to .25v 0 offset-all good-put in 1 1/2 sloblo fuse hooked up to speakers and preamp-played music for 1 hour-got warm -turned bias to .40v 0 offset all good-set bias to .59v o offset-did fine.i then bolted the amp all together and hooked to a different set of speakers turned it on and lost the right channel-dang!! took it apart-slightly melted the fuse but still had conductivity.put in 1a fuse and used variac--left channel okay but right has 22vdc offset p-fet has .4volt bias and n-fet has 0 and the pots don't seem to have any effect--what did i blow up?????helppppp!!!!
 
#1,597
i measure .4v across R11 and 0v across R12 when i have the variac at 115v. when i have the variac set at zero and start to increase to 20v the offset increases and the pots have some effect but past 20v the offset shoots up and the pots have no effect-the offset reads 22v when the variac is set to 115v--please tell me what else to measure and i'll sent back the info-thanks mark
 
#1,599
variac to the complete amp--took board off and had a look around and put back on-have the pots at minimum-turned on the variac when i got to 60-70 volts the offset was at 20v and R1 the 10 ohm resistor was smoking!!!!! that should narrow the search down-any clues to what part is defective? ( besides R1 )🙂
 
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