sub for 2sj50/2sk135

[sasha]

Hi Guys,
Did anyone successfully replace 2sj50/2sk135 with something
I can find easy for 2-3 dollars a piece? I am asking this because I need
a lot of mosfets.
Regards.

[djk]

Lateral FETs are expensive, USD$6.81 in 20+ is about the best you can do.

http://www.profusionplc.com/cgi-bin/...artno=ECF10P20

http://www.profusionplc.com/cgi-bin/...artno=ECF10N20

[sasha]

Hi djk,
Thanks for info.
What kind of problems I can expect if I use say IRFP240?
Or what can be done to circuit to make it work?
Anybody tried this?

[djk]

For an existing design it is too difficult to do.

Bias problems

More gate C to drive

Source resistors needed

Different case style

Tight matching required

Short circuit protection required

[sasha]

I am planing to make Acoustat TNT 200 clone. That amp is specifically
designed for driving electrostatics.
Anyway, after driver board is done I will try to experiment
with cheap Mosfets and include source resistors in design.
If it explodes no big deal, it is only couple of dollars.
You said bias problems. What about it? It won't be stable or what?
Regards.

[Dick West]

Years ago I used a TNT-200 for 5 years with a pair of Acoustat IIa speakers. It is a powerhouse. Did you literally clone this amp? Did you find a source or replacements for the VN01, VP01, etc., devices?

If you want 12 MOSFETs for 65 VDC rails I have them:

http://www.diyaudio.com/forums/showt...932#post660932

Good luck. . .

[Mr Evil]

Originally posted by sasha
...bias problems. What about it? It won't be stable or what?

2SJ50, being a lateral MOSFET, has zero temperature coefficient at ~80mA, whereas IRFP240 has zero tempco at over 6A. Thus IRFP240 will probably require some form of thermal compensation for stable bias.

Furthermore, Vgs is higher for vertical MOSFETs: about 0.4V for 2SJ50 vs. 4V for IRFP240.

[mlloyd1]

For a TNT 200 clone, the SuperTex MOSFETs are tough to find nowdays.
Hafler eventually absorbed Accoustat.
Jim Strickland, who designed the TNT200, refined the concept Trans Nova concept and applied it to Hafler models 9505, 9303, and perhaps some others.
The service manuals (which contain schematics!) may still be available at the Hafler web site - I saw schematics there years ago.
The newer designs are more easily duplicatable with currently available parts.

But they still used lateral MOSFETs at the output. I think you'd be asking for trouble (bias control, larger capacitance, no true complementary pairs available, etc.) trying to use vertical MOSFETs there. But who am I to say ... You might discover something, so have at it.

I've heard the 9505 driving some Soundlab Pristines - very nice :-)

I'm actually surprised more people aren't cloning these designs ....

mlloyd1

Originally posted by sasha
I am planing to make Acoustat TNT 200 clone. That amp is specifically
designed for driving electrostatics.
Anyway, after driver board is done I will try to experiment
with cheap Mosfets and include source resistors in design.
If it explodes no big deal, it is only couple of dollars.
You said bias problems. What about it? It won't be stable or what?
Regards.

[f.k.l.chan]

You can try the 2SK1058 and 2SJ162, it is the replacement from Hitachi which has some Vgs and Id.

[sasha]

Thanks for your replies. I will probably stick to lateral Mosfets.
After all, Acoustat TNT 200 is great amp and worth investing some money.