2sk135 2sj50 matching

[muizel]

I am repairing an sphinx amplifier and have to swab 3 pieces 2sk135 and 3 pieces 2sj50 , what is the best and simple way to match these fet's .

thanks in advance René.

[jacco vermeulen]

Use same batch numbers if possible and match for equal Vgs.
(or Jan de Groot, aka transparantsound.com)

PJ-12 bakkies ?

[muizel]

Hello Jakko,

Yes indeed PJ12, I have replaced the fets and have an offset off about 10 volts !! that is not good. i am now thinking that the ne5534an ic's (2 on top off each other ?) are also bad. I removed and checked all the other semiconductors but they are all in good shape, so I am a bit in a dead end over here.


Do you have any suggestion for me ?

[gain]

is there ~0V DC offset on the other channel? if so, make comparison measurements between the same components on the different channels, starting with the input stage and working toward the OPS. when a reading on one channel differs significantly from the same reading on the other channel, you are homing in on the problem.

[muizel]

Hi gain,

Thanks for the advice, finally they are working it was a 470pf styroflex capacitor with a short This was the first time in many years I had a styroflex with a short never had this before. So I was al the time looking in the wrong way.


Regards René.

[peranders]

Good that you solved the problem.

René mentioned to me that 2 NE5534 was connected "hard" in parallel, on top of each other, has anyone done this or seen this before? Paralleling opamps in this manner is something I would do unless I had full controll over the situation.

[jacco vermeulen]

Originally posted by peranders
seen this before?

One of the British brands, but something you'd do with ceramic case opamps only, not plastic.
(quiescent current level of the 5534 is rather low)

[peranders]

Wouldn't opamps get hot if the offset voltage was too much? It seems like a real budget solution to me.

[muizel]

Hi guy's, just to be sure I just phoned a friend of mine who also has the PJ12 and got him so far to open up the case and inside also the two NE5534 on top of each other.

Any way it is not some sort of modification he is the first owner.

I do find it rather strange the only thing i can think of is that the opamps can deliver more to the rest of the cicuit

Greetz René.

[jacco vermeulen]

Eeh, selected ones ?
They exchanged them for Mr Wurcer's baby when that hit the market, which has a supply current level double as high.

(it's a cascoded supply rail drive thingy, similar to SAC and T&A designs, to name a few)