Sony TA-N77ES Amplifier replacement parts 2SK244

johnp1226

Member
2014-04-03 12:11 am
So I have a Sony Ta-N77ES amplifier that has a bad differential pair (2sk244) and I have not been able to find an exact replacement. I was curious if anyone has run into this issue and if there is a suitable replacement part. It is listed as obsolete everywhere I look. Any help in tracking down the original part or an acceptable replacement would be greatly appreciated.
 

Welcome

Member
2013-03-11 10:52 am
Old obsolete JFETs are super hard to find. This is worse - a dual-JFET in an 8 pin SIL package. A matched pair of 2SK170 or 2SK117 would probably work here but is equally obsolete. At least it is a far more common part, and NOS stock might be able to exist somewhere out there. Keep away from Ebay, unless you want fakes.
 
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Apologies in advance if this is dumb. (Boy, if I had a nickel...)

Is amplifier DC offset a definitive test of input pair matching? In other words, is it possible for a badly-matched pair to achieve low DC offset but still perform poorly in other ways, such as distortion or noise?

What I'm getting at is, at these prices, would it make sense to try a pair or two, measure output offset (relatively easy), then assume the other stuff is OK if offset is acceptable?

Good luck with your big Sony, by the way. Those things are just plain gorgeous, inside and out.

-- Jim
 
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johnp1226

Member
2014-04-03 12:11 am
Jikm,

I understand what you are saying. I am far from a tech but I would assume that it is possible for them to preform badly and have low DC offset. My tech took a look at the link to the parts on Amazon and pointed out there is now way those are genuine parts.

From previous experience I can tell you that fakes are a big problem and they are prone to quick failure and can take out other parts and components so I would say its not even worth trying with parts you are not sure about.

Yeah I get the feeling this might be a couple month thing finding these parts.

Thanks for your help!
 
OK, here's the solution for your tech. :)

The 2SK244 is a Sony designed dual differential 8 pin SIL containing 4 FETs. I think they had it fabricated in the late 70s, so they must have had a big pile of them. They used it from the early Esprit preamplifiers and clearly had plenty of the parts left over even into the early 1990s because many of the 80s/90s ES TOTL models used it.

I have come across noisy ones in the past. Sadly, they are essentially unobtanium now. The TAE77es/d preamps use them, as does the Esprit TAE901 from 1981. Also a bunch of integrateds, TAF555es/444es IIRC.

But here's the deal. A funny thing happened between the TAN77es and the TAN80es power amps (2 years approx apart). Sony must have run out of 2SK244s, so they changed some resistors (R310/311 from 22ohms to 47ohms and R303 from 120k to 150k) and dropped in an NEC uPA68H into the same place on the PCB. Yes, it has one less pin, but two of the pins weren't used on the Sony K244 install in the N77es. The centre pin on the 7 pin uPA68H is substate and not connected- it is an easy drop in.

You can find uPA68h all over the place. Get NEC originals from a reputable source.

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TAN77es front end:
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TAN80es front end:
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block diagram 2SK244:
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**If your tech changes to the uPA68H, make sure he does both channels exactly the same, especially if you want to use the BTL mono function of the N77es.**
 

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johnp1226

Member
2014-04-03 12:11 am
Wow! Thank you Restorer John but we just ordered the parts the Ian Finch recommended but regardless if we have any issues this is great information to have. We ordered enough parts to do both channels but I am betting with out even looking at the links you posted that the option you mentioned is probably the cheaper option. Many thanks and I hope this thread helps other in this same situation. These are the kind of threads that can save people a lot of time searching for parts.