where to find MOSFET ? reuse?

Michael Black wrote:
"robb" (some@where.on.net) writes:
what equipment might i find a MOSFET to reuse so that i do not
need to buy one .

i have lots of electronics equipment just for purpose of hobby
electronic-ing

(vcr, clock radios,various ISA boards {modems, network cards,
router, repeaters, memory expansion, I/O cards, old HDs (not
SMT), wireless messaging phones, TV/monitor PCBs, etc )

any of these more likely to house a MOSFET to be used as MOSFET
buffer for O-scope measure of crystal resonantor (i.e. to avoid
loading due to capacitance of probe)

RF mosfets aren't going to be common. I wouldn't even say they
were dominant at any point, but they were part of a learning curve
and about forty years ago when they became available to end users
they were perceived as the next best thing, with low noise and
good ability to withstand overload and relatively high frequency
response. But oddly, right about the same time the designers
were realizing how to properly use bipolar transistors, tossing
out the notion that the best use for transistors is in low current
use, so bipolars started their rise as good devices for rf
stages.

Now, very few RF mosfets are being manufactured, and while at
one point you likely could have easily found them new, the sources
have dwindled at least in terms of the hobby market.

Which all means that finding equipment that uses them is going
to be lengthy.

Almost a decade ago, I got some mosfets, something like the 3N200,
in "FM preamplifiers" intended for use with car radios. They
were at the dollar store, I bought one for the dollar, opened
it up when I got home and found that it was a mosfet. I went
back and bought the half dozen that remained. A very lucky
find.

The likely most common place to find them, and I don't know how
common they are used nowadays in the application, would be tuner
modules in tv sets or VCRs. Open up the modules, and if you see
any four leaded devices, then they are worth taking a second look
at.

I suppose some FM radio tuners use them still, but I can't say
I've seen them particularly often in such radios. Not likely
in cheap portable radios, but in car radios and more expensive
FM tuners and receivers. But again, there are other devices
so you may have to be opening some or many to find the mosfets.

After that, the most likely places would be two way radio receivers,
but even then it's a roll of the dice. I sure don't see them in
49MHz walkie talkies or cordless phones, and I don't remember
noticing any in the cellphones I've taken apart.

It drops off after that, since you are less likely to come across
esoteric equipment that might use mosfets.

You'll find power mosfets in various things, but again nothing
depends on them, and their specs may not make them suitable for
RF use.

One place you can get them in small quantities, and other
interesting RF parts at reasonable prices is
http://www.danssmallpartsandkits.net
but I haven't ordered from him in over a decade so I don't
know how good the service is nowadays.

In the end, you can probably get by with a jfet buffer, it
will offer a good enough input impedance and many a frequency
counter and oscilliscope input have been made with them.

I can't say you'd find them that much easier in everyday
equipment than mosfets, but maybe a tad more. I've certainly
found them in Delco digitally tuned car radios, the big bulky
ones with green displays, as the first stage in the AM section.
I suspect you will find jfets more common in AM/FM receivers
than mosfets.
Click to expand...
In general, yes, the trend goes towards BJT because they can process
much higher frequencies. ft around 50GHz is quite achievable at low
cost. However, you can still buy lots of RF MOSFETs, mostly dual gate.
Just go to Digikey, key in BF9, then select RF FETs and you'll see that
they have five digit quantities in stock on some. For example 15,000 for
the BF908. Take a look at the BF998, it's a real rocket.

Those things are really handy in building adjustable phase shifters and
such.

--
Regards, Joerg

http://www.analogconsultants.com/
 
"robb" (some@where.on.net) writes:
what equipment might i find a MOSFET to reuse so that i do not
need to buy one .

i have lots of electronics equipment just for purpose of hobby
electronic-ing

(vcr, clock radios,various ISA boards {modems, network cards,
router, repeaters, memory expansion, I/O cards, old HDs (not
SMT), wireless messaging phones, TV/monitor PCBs, etc )

any of these more likely to house a MOSFET to be used as MOSFET
buffer for O-scope measure of crystal resonantor (i.e. to avoid
loading due to capacitance of probe)

RF mosfets aren't going to be common. I wouldn't even say they
Click to expand...
were dominant at any point, but they were part of a learning curve
and about forty years ago when they became available to end users
they were perceived as the next best thing, with low noise and
good ability to withstand overload and relatively high frequency
response. But oddly, right about the same time the designers
were realizing how to properly use bipolar transistors, tossing
out the notion that the best use for transistors is in low current
use, so bipolars started their rise as good devices for rf
stages.

Now, very few RF mosfets are being manufactured, and while at
one point you likely could have easily found them new, the sources
have dwindled at least in terms of the hobby market.

Which all means that finding equipment that uses them is going
to be lengthy.

Almost a decade ago, I got some mosfets, something like the 3N200,
in "FM preamplifiers" intended for use with car radios. They
were at the dollar store, I bought one for the dollar, opened
it up when I got home and found that it was a mosfet. I went
back and bought the half dozen that remained. A very lucky
find.

The likely most common place to find them, and I don't know how
common they are used nowadays in the application, would be tuner
modules in tv sets or VCRs. Open up the modules, and if you see
any four leaded devices, then they are worth taking a second look
at.

I suppose some FM radio tuners use them still, but I can't say
I've seen them particularly often in such radios. Not likely
in cheap portable radios, but in car radios and more expensive
FM tuners and receivers. But again, there are other devices
so you may have to be opening some or many to find the mosfets.

After that, the most likely places would be two way radio receivers,
but even then it's a roll of the dice. I sure don't see them in
49MHz walkie talkies or cordless phones, and I don't remember
noticing any in the cellphones I've taken apart.

It drops off after that, since you are less likely to come across
esoteric equipment that might use mosfets.

You'll find power mosfets in various things, but again nothing
depends on them, and their specs may not make them suitable for
RF use.

One place you can get them in small quantities, and other
interesting RF parts at reasonable prices is
http://www.danssmallpartsandkits.net
but I haven't ordered from him in over a decade so I don't
know how good the service is nowadays.

In the end, you can probably get by with a jfet buffer, it
will offer a good enough input impedance and many a frequency
counter and oscilliscope input have been made with them.

I can't say you'd find them that much easier in everyday
equipment than mosfets, but maybe a tad more. I've certainly
found them in Delco digitally tuned car radios, the big bulky
ones with green displays, as the first stage in the AM section.
I suspect you will find jfets more common in AM/FM receivers
than mosfets.

Michael
 
R

robb

Guest
what equipment might i find a MOSFET to reuse so that i do not
need to buy one .

i have lots of electronics equipment just for purpose of hobby
electronic-ing

(vcr, clock radios,various ISA boards {modems, network cards,
router, repeaters, memory expansion, I/O cards, old HDs (not
SMT), wireless messaging phones, TV/monitor PCBs, etc )

any of these more likely to house a MOSFET to be used as MOSFET
buffer for O-scope measure of crystal resonantor (i.e. to avoid
loading due to capacitance of probe)

thanks for any help,

robb
 
In article <13ih7m8nc6ocr3a@corp.supernews.com>,
"robb" <some@where.on.net> wrote:

what equipment might i find a MOSFET to reuse so that i do not
need to buy one .
Click to expand...
Just check numbers from various likely-looking parts. If it has an IR
with a diode-looking symbol inbetween the I and R, there's a good bet
(International Rectifier - they do make other things, but they make a
lot of MOSFETS, some in packages you might not expect). There's
half-a-dozen duals in 8-pin packages on a particular flavor of dead hard
disk board I have, but those are SMT, and non-SMT hard drive boards are
probably very old, IME.

If you find a Philips part, you need to look at NXP for the datasheets,
as Philips does not even redirect you there, or admit that they ever
made parts on their website.

--
Cats, coffee, chocolate...vices to live by
 
"robb" <some@where.on.net> wrote in
news:13ih7m8nc6ocr3a@corp.supernews.com:

what equipment might i find a MOSFET to reuse so that i do not
need to buy one .

i have lots of electronics equipment just for purpose of hobby
electronic-ing

(vcr, clock radios,various ISA boards {modems, network cards,
router, repeaters, memory expansion, I/O cards, old HDs (not
SMT), wireless messaging phones, TV/monitor PCBs, etc )

any of these more likely to house a MOSFET to be used as MOSFET
buffer for O-scope measure of crystal resonantor (i.e. to avoid
loading due to capacitance of probe)

thanks for any help,

robb
Click to expand...
You may find something suitable in the RF front end in RF devices.
 
"Ecnerwal" <LawrenceSMITH@SOuthernVERmont.NyET> wrote in message
news:LawrenceSMITH-D800A3.12321031102007@news.verizon.net...
In article <13ih7m8nc6ocr3a@corp.supernews.com>,
"robb" <some@where.on.net> wrote:

what equipment might i find a MOSFET to reuse so that i do
not
need to buy one .

Just check numbers from various likely-looking parts. If it has
an IR
with a diode-looking symbol inbetween the I and R, there's a
good bet
(International Rectifier - they do make other things, but they
make a
lot of MOSFETS, some in packages you might not expect). There's
half-a-dozen duals in 8-pin packages on a particular flavor of
dead hard
disk board I have, but those are SMT, and non-SMT hard drive
boards are
probably very old, IME.

If you find a Philips part, you need to look at NXP for the
datasheets,
as Philips does not even redirect you there, or admit that they
ever
made parts on their website.

--
Cats, coffee, chocolate...vices to live by
Click to expand...
thanks ecnerwaL,

yes the non SMT drives are very old indeed 340 meg scsi , the
PCB was a lovely foray into SMT tecnology with leed-less
resistors and small tiny wire wound inductors in tiny plastic
box mounted to surface of PCB
with many other SMT sized ICs


thanks again,
robb
 
"Gary Tait" <classicsat@yahoo.com> wrote in message
news:Xns99DC65557F489wonkynillmailnil@142.77.1.194...
"robb" <some@where.on.net> wrote in
news:13ih7m8nc6ocr3a@corp.supernews.com:

what equipment might i find a MOSFET to reuse so that i do
not
need to buy one .


You may find something suitable in the RF front end in RF
devices.
Click to expand...

thanks for help gary,
robb
 
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