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Sony TA-E88 FET Replacement Problem

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May 20, 2004 9:55:49 AM

Archived from groups: rec.audio.tech (More info?)

Hello

Can anyone advise me on replacing a blown dual FET device that has blown in
the buffer stage of my pre-amplifier.
It is marked "IT 500"

I contacted Sony but they say it is obsolete.

This is the spec:
GE Intersil Monolithic dual Cascoded N channel JFET
CMRR >120dB
Gate Operating Current: -5pA (VDG35V ID 200µA TA 125°C)
Drain-Source & Drain-Gate Voltages: 60V
Drain Current: 50mA per transister
Gate to Gate Voltage: ±60V
Gate to Source Cut-off Voltage(min/max): -0.7/-4V (VDS 20V ID 1nA)
gfs 1kHz(min/max): 1000/4000µS (VDS20V VGS0V)
gfs 1kHz(min/max): 500/1600µS (VDS20V ID200µA)
en 10Hz/1kHz: 50/15 µV/?Hz

I can email the part of the circuit diagram that shows the FET in situ if
this will help.

Thanks
Gary

To reply by email remove (sp10)
May 25, 2004 11:30:53 PM

Archived from groups: rec.audio.tech (More info?)

"Gary" <firestormvtr(sp10)@btopenworld.com> wrote in message news:<c8hh95$bdq$1@hercules.btinternet.com>...
> Hello
>
> Can anyone advise me on replacing a blown dual FET device that has blown in
> the buffer stage of my pre-amplifier.
> It is marked "IT 500"
>
> I contacted Sony but they say it is obsolete.
>
> This is the spec:
> GE Intersil Monolithic dual Cascoded N channel JFET
> CMRR >120dB
> Gate Operating Current: -5pA (VDG35V ID 200µA TA 125°C)
> Drain-Source & Drain-Gate Voltages: 60V
> Drain Current: 50mA per transister
> Gate to Gate Voltage: ±60V
> Gate to Source Cut-off Voltage(min/max): -0.7/-4V (VDS 20V ID 1nA)
> gfs 1kHz(min/max): 1000/4000µS (VDS20V VGS0V)
> gfs 1kHz(min/max): 500/1600µS (VDS20V ID200µA)
> en 10Hz/1kHz: 50/15 µV/?Hz
>
> I can email the part of the circuit diagram that shows the FET in situ if
> this will help.

Hmmm seems like that is the same model number as a sony switch mode power
supply amplifer from the late 70s... whatever.

Suggest that there is nothing I know of that is a "Cascoded N channel JFET"...
at least in a single package... If there was then you will have to fake it
with two FETs...

Send me a copy of the schematic and I can tell you what it is...

Anyhow you'll need to spec the B+ (Vds) for the devices, spec the actual
IDSS (easy enough to test) of the good devices, and then select some current
production FETs that happen to meet these two specs... Done.

The IDSS may or may not be important depending upon how they were used in
the circuit.

I may have some N ch fets sitting here and a way to match them... would have
to check if they are all P ch or N ch, don't recall...

Regards,

_-_-bear


http://www.bearlabs.com
>
> Thanks
> Gary
>
> To reply by email remove (sp10)
May 27, 2004 1:09:39 AM

Archived from groups: rec.audio.tech (More info?)

Looks like a combo that is definitely no longer available.
But you can make one up by simply taking 4 fets and combining
them into the same circuit!

It would be good to have the lower two fets be a "matched" pair -
meaning a DUAL fet in a single package (6 leads).

The upper two fets should be close, or just another one of the
same as the lower fets. take a little perf board and fab up a
mini module, follow the wiring as shown...

You can probably use almost any 2SKxxx FET around...

How do you know the input fets are blown?

BTW, you'll have to change both channels.

_-_-bear


"BEAR" <bearlabs@netzero.net> wrote in message
news:a81234ee.0405251830.7894f84b@posting.google.com...
> "Gary" <firestormvtr(sp10)@btopenworld.com> wrote in message
news:<c8hh95$bdq$1@hercules.btinternet.com>...
> > Hello
> >
> > Can anyone advise me on replacing a blown dual FET device that has
blown in
> > the buffer stage of my pre-amplifier.
> > It is marked "IT 500"
> >
> > I contacted Sony but they say it is obsolete.
> >
> > This is the spec:
> > GE Intersil Monolithic dual Cascoded N channel JFET
> > CMRR >120dB
> > Gate Operating Current: -5pA (VDG35V ID 200µA TA 125°C)
> > Drain-Source & Drain-Gate Voltages: 60V
> > Drain Current: 50mA per transister
> > Gate to Gate Voltage: ±60V
> > Gate to Source Cut-off Voltage(min/max): -0.7/-4V (VDS 20V ID 1nA)
> > gfs 1kHz(min/max): 1000/4000µS (VDS20V VGS0V)
> > gfs 1kHz(min/max): 500/1600µS (VDS20V ID200µA)
> > en 10Hz/1kHz: 50/15 µV/?Hz
> >
> > I can email the part of the circuit diagram that shows the FET in situ
if
> > this will help.
>
> Hmmm seems like that is the same model number as a sony switch mode power
> supply amplifer from the late 70s... whatever.
>
> Suggest that there is nothing I know of that is a "Cascoded N channel
JFET"...
> at least in a single package... If there was then you will have to fake it
> with two FETs...
>
> Send me a copy of the schematic and I can tell you what it is...
>
> Anyhow you'll need to spec the B+ (Vds) for the devices, spec the actual
> IDSS (easy enough to test) of the good devices, and then select some
current
> production FETs that happen to meet these two specs... Done.
>
> The IDSS may or may not be important depending upon how they were used in
> the circuit.
>
> I may have some N ch fets sitting here and a way to match them... would
have
> to check if they are all P ch or N ch, don't recall...
>
> Regards,
>
> _-_-bear
>
>
> http://www.bearlabs.com
> >
> > Thanks
> > Gary
> >
> > To reply by email remove (sp10)
!