2SK134/2SJ49 for output of Counterpoint SA-12??

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kilohertz

kilohertz

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Joined 2006
#1
Hi Gang,

Apologies for moving this post...I put it in tubes as the amp has tubes...but thinking about it, this is more of a solid state question. Sorry for the dupe post.

And now, on with our show....:smash:

Relatively new here, but been building hi end audio since the early 80's...

I have just dug out my old Counterpoint SA-12 after 10 years of storage and found a bag of MTM12N10's strapped to the side. Mmmm...seem to remember something about one channel failing??

Well, upon removal of the FET caps, I see that it has been repaired before with IRF130's and the /\/\ mentioned above. Well, knowing how fussy this amp is with using matched output devices, it's time to fix it properly. I have searched the web for the last 2 days and can't find any hard evidence of reasonable subs. I believe the original MOSFETs had PTC characteristics, and that seems to be hard to find in complementary pairs. Then I remembered I have 2 flats of 2SK134/2SJ49's sitting in my pile of valuable junk in the shop and thought I'd dig up the specs on those. Can't find temp curves but it looks from reports, that these had positive temp coef. as well. They are rated at 7A instead of 10 or 12, but they were still sucessfully used in pairs in 100WPC amps.

Your thoughts? Can I just drop these in, rebias to around 100-200mA and go? I think the drain source pins may be reversed on htese but that is an easy fix.

Cheers

Paul
 
#4
Depends at minimum on the voltage on the rails and how much voltage the devices will see across them...

Positive tempco? Not sure this is correct, they turn off as they get warm... up to a point, beyond which they can't turn off anymore. But in a properly designed and heatsinked amp they don't run away.

The bias set on the amp may not have enough range to turn off enough to properly bias the Hitachi devices, as the IRFs take more voltage.

I have the spec sheet on the Hitachi devices, but not handy and not in a form I can post very easily right now - I am about 25mi from them until the weekend. They ought to be out on the web?

Worst case they blow up?

_-_-bear
 
#7
turnA_zpoint,
reducing Crss is a big and important improvement (8/18pF instead of 10/40pF), extremely impressive, good for linearity. The input capacitances (Ciss) are not much smaller (600/800pF, before 600/900pF) so they are not much easier to drive.
Do you know anything about the manufacturing?
 
#8
Hi Lumba Ogir
I don't know about the manufacturing the MOS FET process.

But for designing a circuit,some .. many Guy may know already ... ,from my TEXT book following
******************************
"Then ....Ciss=600pF and Crs=70pF, the input resistance for DC over 20Mohm
So input resistance(Impedance) is due to the input capacitance (Ciss) and input frequency,

2.38Kohm in 100KHz
23.8Kohm in 10KHz
238Kohm in 1KHz

But In the state of working actually,
the input capacitance : to 1/(1+|Yfs|*R(load)) because it decreases.

for example |Yfs| =2S ,R(load)= 8ohm
the actually capaciance becomes 1/17,So, 17 times input impedance rises.

　In this case, if the output impedance of the voltage amplification steps is low, the influence becomes small though the input impedance will change by changing of R(load)."

********************************
So low Ciss MOS FET is able to less driver step.

Though,driver is not simple,
I use 2SK3497/2SJ618 (Ciss = 2400pF/3500pF) ,it's better than using 2SK1529/2SJ200 (Ciss = 700pF/1300pF) in my room.

I think this may be the |Yfs| of 2SK3497 is 12 (standerd!) ,so have high danping facter ,and so on..

Regards
 
#11
turnA_zpoint,

2S2SK134/2SJ49
2SK2221/2SJ352
2SK60/2SJ18
2SK1529/2SJ200
2SK2955/2SJ554
2SK3497/2SJ618
represent superior Japanese technology.

2SK1529/2SJ200 High resolution
2SK3497/2SJ618 Powerful
Right.
You need much power, lateral FETs are more restricted in that regard.
 
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