ID a FET or BJT

[Watson A.Name - \"Watt Su]

I ran into this schematic of a FM preamp, which has a standard BJT self
biased circuit with the resistor between base and collector. However
they give the part number as MFE201, which is a Motorola FET in a metal
case. The MFE was used by Motorola and I have some of their datasheets
in my old Moto Manual, but they're all four digits after the MFE. And
they're all FETs which won't work in this circuit. I did a google
search and came up with just a few hits, all dead ends.

http://www.uoguelph.ca/~antoon/circ/activefm.html

I'm thinking that it might work with a VHF BJT, but these tuned input
and output amps tend to oscillate without neutralization. So it's
important to get the right BJT. Thanks.

--
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@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[mc]

I was writing for Popular Electronics in 1996, but it isn't mine. I'm
guessing the schematic was mis-transcribed. If sufficiently motivated I may
go and look and see if I can find it. Can the person who posted the circuit
tell us which issue and page he got it from?

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:11662r0r4897c7f@corp.supernews.com...

I ran into this schematic of a FM preamp, which has a standard BJT self
biased circuit with the resistor between base and collector. However
they give the part number as MFE201, which is a Motorola FET in a metal
case. The MFE was used by Motorola and I have some of their datasheets
in my old Moto Manual, but they're all four digits after the MFE. And
they're all FETs which won't work in this circuit. I did a google
search and came up with just a few hits, all dead ends.

http://www.uoguelph.ca/~antoon/circ/activefm.html

I'm thinking that it might work with a VHF BJT, but these tuned input
and output amps tend to oscillate without neutralization. So it's
important to get the right BJT. Thanks.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Michael Black]

"Watson A.Name - \"Watt Sun, the Dark Remover\"" (NOSPAM@dslextreme.com) writes:

I ran into this schematic of a FM preamp, which has a standard BJT self
biased circuit with the resistor between base and collector. However
they give the part number as MFE201, which is a Motorola FET in a metal
case. The MFE was used by Motorola and I have some of their datasheets
in my old Moto Manual, but they're all four digits after the MFE. And
they're all FETs which won't work in this circuit. I did a google
search and came up with just a few hits, all dead ends.

http://www.uoguelph.ca/~antoon/circ/activefm.html

I'm thinking that it might work with a VHF BJT, but these tuned input
and output amps tend to oscillate without neutralization. So it's
important to get the right BJT. Thanks.

It's the sort of circuit where you'd see the 2N918. Oddly, it

crosses at the ECG site to the ECG108, basically the same as
one the bit mentions (though I didn't do a direct comparison).

I don't think the exact type is going to matter. It's a cheap
FM preamp, and it's not likely to work that well anyway. It's
bound to overload in an urban area, and as you say oscillate.
But it's the configuration that will oscillate, not the particular
bipolar transistor. SOmething with reasonable gain, and a high
bandwidth is what's needed; pull one off an existing FM tuner,
or an old TV tuner. Or for that matter, copy the the full circuit
from the FM tuner.

A few years back I came across "FM preamplifiers" in a dollar
store, selling for an actual dollar if I recall. They were in
the window, so I went in and bought one. Turned out to use an
actual mosfet, so I went back and bought the three or four that
remained. The circuit was very simple, not what you'd expect to
find in decent equipment. I never even tried one out.

Most FM tuners are too sensitive, and an amplifier won't do anything
even if it does work.

Michael

 

[Watson A.Name - \"Watt Su]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com>
wrote in message news:11662r0r4897c7f@corp.supernews.com...

I ran into this schematic of a FM preamp, which has a standard BJT
self
biased circuit with the resistor between base and collector. However
they give the part number as MFE201, which is a Motorola FET in a
metal
case. The MFE was used by Motorola and I have some of their
datasheets
in my old Moto Manual, but they're all four digits after the MFE. And
they're all FETs which won't work in this circuit. I did a google
search and came up with just a few hits, all dead ends.

http://www.uoguelph.ca/~antoon/circ/activefm.html

I'm thinking that it might work with a VHF BJT, but these tuned input
and output amps tend to oscillate without neutralization. So it's
important to get the right BJT. Thanks.

--

Well, I found a source for those elusive MFE201s. Ebay.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7508025322&rd=1&sspag
ename=STRK%3AMEWA%3AIT&rd=1

Howsomever, they're worthless for this circuit. They are dual gate
MOSFETs, which are nowheres near what the circuit needs. I think antoon
is just
making another huge boo-boo, as he has done in many other schematics.