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akersa 29th March 2003 09:59 PM

2sk135 2sj50
Does anybody know where I could find datasheets for 2sk135 and 2sj50 transistors. I am working on a amp and I need to know the specs on the transistors.



peranders 30th March 2003 05:52 AM



akersa 30th March 2003 06:56 AM

Thanks for the data sheets. They were a big help.

Adam Akers

peranders 31st March 2003 08:36 PM

Lot's of guys here (including myself) have built amps with K135/J50 so if you want some input ask. :bulb: :scratch:

Sjef 2nd April 2003 10:31 PM

Hai Peranders,

I have a hybride amp wih the K135/J50 combo. It's running in Classe A with a bias voltage of round 1 Volt. I'm using them only for my woofers now (100Hz/24db crossover) and therefore I would like to change the operating point to Classe AB to run things less hot.

Have You any idea how low the bias voltage can go without sacrifising linearity. The amps are running without negative feedback.

peranders 8th April 2003 08:04 PM

The K135/J50 are rather special, they have constant gm over a certain current! This is good for linearity but bad for output impedance. Since it is about bass, just use your ears! Turn down the idle current until you actually can hear the crossover distorsion. Play at approx. 1 volt output signal. The sound will be like a burned voice coil, like it scratches towards the magnet.

Sjef 8th April 2003 10:19 PM

Yes this combo behaves a bit strange indeed. I'll just try it with a potmeter. Thanx

peranders 9th April 2003 07:59 AM

K135/J50 without feedback is rather unsuitable I think. Rather high output impedance (1- 0.5 ohms with one pair) together with a very varying load. I suspect this can colour the sound quite a bit!

Sjef 9th April 2003 09:11 PM

It always worked pretty fine without feedback. I used two pairs of per channel. I don't worry to much about output impedance, up to 1 Ohm is okay, my loudspeakers don't mind. The Fets sound very powerfull in combination with the mu-stage I used as a driver, but it simply just does not have the "magic" of a good tube amp. I've tried them with overall feedback but I found that the gain in control and speed didn't weight against the loss in air and detail. It sounded somewhat nervous with the feedback and began to sound more like an all transistor based amp.

Personally I think there are better sounding Mosfets nowadays.

jean-paul 9th April 2003 10:17 PM

K135/J50 work fine without feedback. Never had any problems and I didn't notice coloration.

I don't use any resistors, the MOSFETS are coupled directly ( I do use "gridstoppers", resistors to the gate ). Made quite a few amps with them that still run after 10 years of uninterrupted use ( always on ).

In my amps I ran them with 400 mA- 500 mA idling current. When not used curent was switched to a low value for prolonging the life of the devices. They do suffer from aging when used in class A.

Still like them very much despite TO 3 case and the trend of thinking that newer devices are better. Technically maybe right but soundwise K135/J50 really are OK. Never saw one that failed BTW ! Even saw an amp that had the devices "swapped". It didn't work but the FET's survived :bigeyes:

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