Sony TA-E88 Fet Replacement Problem

[zedrider]

Hello

The above device is used in the buffer and line stages of a Sony TA-E88 pre-amplifier, one of them has gone , i have searched all over for one and cannot find any.

I tried replacing the fet with 4 2SK30a fets which worked but not very well, i could not get "0" volts between the two sources of the fets.

So

I am wondering if anyone knows where i can find one these or has some that would be willing to sell to me or knwos of a way around the problem, i have uploaded a jpeg of the circuit showing the original fet in circuit.

Thanks
Gary
http://www.btinternet.com/~swlthr/ebay/IT500.jpg

[janneman]

Hi Gary,

I own one of these per-amps, unfortunately I have no spares. But did you try to adjust the balance with Rt301? I would expect that that is necessary even when replacing them with the original IT500's.

Another option would be to buy a bunch of fets that come close and select a matched quad.

Jan Didden

[zedrider]

Hello Jan

Thanks for your reply.
Yes i have tried setting the offset voltage with the pre-set but i cannot get less than 300 mv dc on the output, if try the working It500 from the other channel it works.

Gary

[janneman]

You could try two pairs of two matched fets, or two pairs of two in a single package.

Wait, did you try to swap the individual fets of the four you have used? There must be a combination that lets you get to zero, I would think.

Jan Didden

[zedrider]

This is a problem, i do not know how or where to buy matched fets, i know sony used to make matched pairs in a 6 pin package (2SK97) but i cannot find these either.

Fets are not my thing when it comes to understanding them.

Gary

[tvi]

The were made by ge/intersil, I have a data sheet somewhere.

Either HP or Tektronics used them, but using an in house numbering system, If I can find it I will post the cross reference.

Regards
James

[zedrider]

Hello James

Thanks for that, could be worth a try.

Gary

[janneman]

No, they were definitely packaged in a SONY marked package. I have a source that still had similar chips for a TA-N88. I bought all their stock of it, 6 pieces.
I will call them next week for this, small chance buth worth a try.

Jan Didden

[zedrider]

Hello jan

Thanks for that, the ones i have in my pre-amp are just marked "IT500" followed by a date.

Just out of interest, some of the tantalum capacitors failed in this pre-amp, which what i think caused the fet to blow, so i changed every single tantalum cap for a stargetz audio grade electrolytic capacitors, not only did this solve some of the problem but it improved the sound aswell, making the sound a little richer and the soundstage wider.

Gary

[zedrider]

<<<<No, they were definitely packaged in a SONY marked package. I have a source that still had similar chips for a TA-N88. I bought all their stock of it, 6 pieces.
I will call them next week for this, small chance buth worth a try.

Jan Didden


__________________
/ The brain is logical - the mind may not be>>>

Tell me Jan

what sort are the ones you have for the TA-N88?

Gary