Dual Gate Mosfets DATA and Information Page Earl VE3AB -- www.hamelectronicsmagazine.com and the other site:
www.earlandrews.com (a mirror site). - selling parts in small quantities to hobbyists and tinkerers since 2005 by the web
and mail order.
BF981 (I now have about 50 for sale/in stock).

I bought some of these in bulk ie lots of 20 or so.
They are much less in cost than the RCA 40673 discontinued dg mosfet.

Enterprising hams can perhaps adapt these to their circuits or solder fine transistor
lead material to the axial leads thus creating radial wire leads.

I'll take some pictures when I try this myself in the near future.

Even though it is gate protected with back to back diodes...I would use a ground
strap or ground yourself frequently when handling.
BF981 PICTURED BELOW. -- COMMONLY AVAILABLE AT A REASONABLE PRICE from
various sources. I see numerous listings on ebay. I sell them in small quantities for
$2.00 each with low postage charges. I have about 40 or 50 currently in stock. Sellers in
Hong Kong are offering them for less with free shipping. I can ship them here from
Northern Ontario by letter/post $1.50 across Canada and $2.80 to usa.

note: ON THE BF 981..if you want to try a few of my "modded"bf981s with radial leads..in
your circuit..I can make some up and sell them at $4.75 each. -- For that price I will also
test them in my FT301 transceiver front end circuit (plug in socket).

NOTE: I found they work very well as an RF front end transistor.
rca 40673 (nte (an aftermarket distributor) NTE222
(ecg 222)
At a fast glance at the specs, the drain current is
less than half for this bf981 than the 40673.

Perhaps the DC biasing voltages and currents might
have to be altered (resistors/dc voltages).

Iam a technician not engineer. For the low price of
these devices, I would be inclined (myself)to try it in
the circuit as a direct substitute for the 40673 and
see if it works.

I did this very thing with the FT301 radio I was
working on. I tried a substitute device and it worked
and (in fact) seemed to work as well or better than
the original dg mosfet.

I belong to a list QRP-L. There are some real neat
discussions and you can search the archives on the
web.

SOME OF THE POSTS ABOUT 40673 DG MOSFETS and
substitutes are in text at the bottom of this page.
NTE/ECG are good aftermarket sources but can be a bit
pricey.

NTE has an on line CROSS REFERENCE TOOL and you can
download PDF files of the data sheet.

One ham in NewFoundland that I chat with the odd time
paid about $20 for a dg mosfet aftermarket device.

I can supply you at a much lower price.

I keep all my DUAL GATE MOSFETS in static packaging and
in a metal cabinet.

I don't have a great deal of stock of these items but I can
supply up to a few at a time if you need to fix or build
something.

NOTE: THE METAL CAN PACKS LIKE THE 40673 and other
metal can packs are fairly pricey to buy most places and I
have to pay shipping on top of that..SO..I can only sell
MAXIMUM of 2 metal can pack DG MOSFETS per order.
BELOW IS SOME "IDEAS" PRESENTED BY PEOPLE ON VARIOUS FORUMS on the internet concerning substitutes for common dg
mosfets ---
I HAVE NOT verified if these ideas are completely true or not but they are presented to tinkerers and hobbyists LIKE
HAM experimenters and circuit builders.

According to my 1975 MOSFET Circuits Guidebook the RCA 40673 is a "consumer-type" substitute for the RCA 3N187, not that the 3N187 is
any easier to find.  It is an N-channel depletion-type MOSFET with diodes protecting the gate.
-----------------------
If you want to deal with surface mount components, and there is nothing wrong with doing that, there are several parts that will replace it, try
the BFR991, BFR994, and with some care watching the Vds, the BF998. The good news is that these are all less than a buck at Digikey.  
------------------------------------------------
I am trying to complete a receiver project from the ARRL HB(1980's) and find
> myself in need of RCA 40673's. I see them listed on eBay at a price of $6+.
> Is there any one selling these at a more resonable price? I realize these
> have not been generally used in the last 10 years or more.
> Possibly some one can suggest an inexpensive replacement?

A BF981 or something like it should work. The package is different, though.
(my note: this is the one I would try as a substitute myself
noted by me Earl Andrews VE3AB..note..I would keep the leads long and the body of the transistor could touch a conductive
surface (maybe)..keeping the leads long (not cutting them off short) would/could dissipate the heat.
---------------------------------------------------
NTE has a substitute NTE222.  You may try some vendors who sell NTE
transistors.  Another substitute is the 3N201.  This may require some bias
adjustment, however, I have substituted these directly for a 40673
---------------------------------------------------
SUBSTITUTES FOR THE VERY POPULAR RCA 40673 Dual Gate
Mosfet. Discussion from QRP-L the Low Power QRP and technical
group I subscribe to. As one fellow says : ARRL 1980s Handbook
had a few receiver projects and other radio projects that used dual
gate mosfets such as the RCA 40673.
Whatever subsitute you try: try to get the one with diodes
protecting the gate. My Ten TEc Argonaut 505,509 and 515 use a
dual gate mosfet in the RF amplifier stage. Back to back diodes on
the antenna line to the receive RF amp (DG Mosfet) will aid to
protect against static spikes which can damage these high
impedance devices. Make sure you ground yourself before and
during handling. Store them in a static safe storage bag with
antistatic foam on the leads or a wire shorting out the leads.
40673 substitutes listed at the bottom of the page.
These "house numbered" dual gate mosfets were bought by
me back in around the year 2000 or so from a fellow on QRP-L
(the technical and qrp list I belong to).

I bought them way back when and our dollar was only worth
about 65 cents or 70 cents to the american dollar.

I can spare a few for $1.75 each. I think they are similar to
3n211 (I can look it up).

I used one by forming the leads and it worked quite well in
my FT301 replacing a dual gate mosfet in the rcvr front end. I
also used them in a converter that had a couple of damaged
dg mosfets. Seemed to work ok but I need to evaluate the
circuit under real world conditions.

I CROSS REFERENCED THE MPF 131 TO BF 981,3SK49, MFE131
(electrically quite similar).

ID LIKE TO BUY MORE OF THIS KIND
OF STUFF IF ANY ONE HAS ANY TO
SELL.
actually..I'm starting to run
low on stock of DG mosfets.
With these house numbered Dual Gate Mosfets  (see correction on this
page)..these parts are MEM631s and the -11 in suffix (for a complete part
number) would indicate pre-bent and cut leads.The pin out is a similar layout
to the metal can package dg mosfets and with a bit of lead forming they can
be used in place of the radial lead transistors. I did this with my FT301 on the
RF board and the circuit worked as well or better with this substitute.
To the left (pictured) the little pin out sheet that came with these DG
MOSFETS.

For $1.75 each they are inexpensive and seem to work. I used them in a
vhf converter that I repaired and they worked ok there as well.

DIODE PROTECTED GATES ON THESE ONES AS WELL.

HANDLE WITH CARE THOUGH..I WOULD GROUND MYSELF BEFORE AND
DURING HANDLING UNTIL THEY ARE SOLDERED INTO THE CIRCUIT.


ESD  ELECTRO STATIC SENSITIVE DEVICE
MOSFETS ARE PRONE TO ESD DAMAGE.
I can supply a few of these DG MOSFETS that are similar to MPF 131s.
Update/Correction: these house numbered dg mosfets are apparently NOT
house numbered this according to a fellow who wrote me an email
(BOB in Toronto.)>>>
Your "house numbered mosfets" are NOT house numbers but old General
Instruments dual-
gate n-channel mosfets.
They could not print the entire part numbers on these devices plus the
datecode (705,
which I assume is for 1977, in the 5th week) and make it readable so they only
put the
end of the number on.
The 31-11 is an "MEM 631" (the -11 is for the pre-bent and cut leads option)
and I have
scanned the datasheet for you from the 1978 General Instruments databook I
still have.  
(MY COMMENT: hooray for old data books!! I wish I had kept all the
data books when they threw them out at work!! There is no better way to look
up and identify items (especially the old stuff-- earl)

Future Electronics way back then sold them for only $0.90 (I still have the price
list
page if you want a copy, but they are certainly worth a lot more now.)


I am just taking a quick look at your site.
The MM5871 is an old National Semiconductors MOS chip. It's a "Rhythm
pattern
generator" which would be used in something like an old Hammond organ.  I
have the full
data on that too.
I hope this is a help.
Bob in Toronto, On. CANADA
http://www.datasheetarchive.com/  is
where I get most of my data sheets and
cross references-- it is great but I could
not find the RCA 40673 listed there. I
used the NTE semiconductor web site to
find info and pdf file for this one.
What we have here is the underside of the circuit
board and
a group of spare dual gate mosfets.
The dual gate mosfets are some in house part
number used by some company but are (supposedly)
similar to type 3n201 dg mosfets.

REPLACING THE METAL CAN PACK DG MOSFETS (2
OF THEM-- with these economical plastic case dg
fets).

When mounted on the top (component side) of the
circuit board; the pin layout
does match the pattern
layout
but the pins themselves are too thick to go
through the holes in the circuit board. (and they
would likely have to be formed to the physical layout
dimensions).

As a work around solution; I flipped the leads upside
down with a pair of pliers and clipped them and
formed the leads and mounted them upside down on
the bottom of the circuit board.

This is "OK" for amateur use. Commercial vendors
and manufacturers would not do this unless they
could not avoid it.x vh
Where I used to work for 18 years (with Military and ex Military Technicians and supply people) I was sternly told that "work around solutions"
were not the way to do things. --- NOW that I am on my own and this is 'AMATEUR' equipment that does not see any g-forces or does not have to
withstand blasts or vibrations or stresses of that nature.. work around solutions that make sense and save money are the order of the day.

This is an 2 meter receive converter than ouputs on 27 mhz! A bit of a rare item. Picked it up at a flea market for $2 w/manual. Both DG Mosfets
needed to be replaced. The converter now works. Not sure if it is low noise and good sensitivity or not. I have not gotten around to comparision
tests yet.

Up here in northern ontario, 2 meter ssb activity is not that common and I dont have a good horizontal beam so I have not put this converter to
the test (yet).
2 dual gate mosfets replaced on the opposite side of the circuit board from
the component side. I formed the leads and the chip is actually upside down
on the circuit board. Work around solution that works! --- The converter now
works!! This could work as well for the
Navigation Link to
www.hamelectronicsmagazine.com/qrpparts
MY LIST OF AVAILABLE PARTS (Dual Gate MOSFETS)

RCA40673 (I do have a few available) these are discontinued parts (discontinued in the
1980s) -- I now have a good quantity of RCA40823 (very close spec to 40673) available
for $3.90 each!!
For one or two 40673s (THE REAL MCCOYS)..I can send in an envelope. I dont have a
whole bunch I can spare however. $7.50 each plus economy postage $1.50 Canada

BF981...I have about 40 or so available. about $2 each (economy postage of $1.51
Canada wide and $2.80 ..I can send these little parts to you in ESD safe padded
envelope. -- small orders OK..no minimums

3N211 I have a few I can spare..these FETs are favourite replacements in front
ends of older radios.-- these are good for RF front end stages ie FT301 and
perhaps argonaut 509 as well.-- I sell them tested guaranteed - $7.50 each

SFE1612 - dual gate mosfet: I have found through testing in my FT301 receive
section..(RF gain stage and mixer) that the SFE1612 has a tad bit more gain than
the 3N211. I sell the SFE1612 for $5.75 each and I have about 60 in stock.
SFE1612 seems to be some sort of Motorola Proprietary device and data sheet
and information seems to be not available! Once I did actually phone Motorola
for information about an SRF series of Proprietary Transistor and they dont tell
you much about these types of products. -- All I know is the SFE1612 is nr. one
on my list. Drop in replacement for 40673 or 3N211 or others.




MEM 631. I can spare some of these. I adapted the leads to a transistor socket in
my FT301 front end and this dg mosfet performed a bit better than the original
(or so it seemed to me). MEM631-11 (The -11 is for the FORMED LEADS..(SEE THE
PICTURE OF THEM ON THE BLACK ESD BLOCK FURTHUR DOWN THE PAGE.

You can mount them upside down on a circuit board and solder them in. Ive
done this too as a "fix" ...at $2 each they are an inexpensive alternative.
**see picture near bottom of page on how I soldered them on a circuit board (on
the bottom of circuit board rather than on top (component side)





NOW AVAILABLE ..3SK97 Gaas FETs..4-- ill sell at $22 each..with economy postage.
BF981 extracts from DATA sheets. Full data sheet available:
datasheetarchive.com
NAVIGATION LINK to
www.ham
electronicsmagazine.com < a free on line ham radio
magazine by Earl Andrews VE3AB> 73 Earl VE3AB
LINK HERE TO GO TO THE HOME PAGE
The 3N211 seems to be a bit better
than most dual gate mosfets for
front ends of receivers.

I do have about a dozen or so that I
have carefully bought over the past
few years from hobbyists and from
ebay vendors ect.

I sell them for a very small mark up
of only about 20 to 30 percent on
average. So I am selling them at\
$8.00 each plus the usual low
postage charge of $1.51 in Canada,  
$2.80 in USA and about double that
for overseas.

I am limiting the quantity to 2 per
order/customer.
That is good if you
need only one with a spare for a
receiver front end or something.

All these DG MOSFETS..the metal
can types are AS QUANTITIES LAST.  
I will try and buy some more stock
but in the mean time..perhaps try
places like EBAY the greek sellers.
They seem to have some good stuff
at good prices.
Scotts Radio Parts ie crystal radio
parts..you can google him  and he
sells the 40673 and some others
reasonable..but he cautions as
well..WHILE QUANTITIES LAST!

The 40673 is a discontinued part.
MEM631 DG MOSFET DATA SHEET FILE (PDF) LINK
HERE TO THIS FILE
OCT 27-2012..see my new article I have just written on how to convert the BF981
into a radial lead DG mosfet in order to provide a direct plug in replacement for
metal can dg mosfets such as 3N211, 3SK45, rca 40673..
ARTICLE IS HERE...
DUAL GATE MOSFETS.. 40823 40820 (SOLD OUT!-) I still have lots of others
- old Texas Instruments 3N201 (1972 date code) TESTED by ME. Good only $3
while qty lasts. I currently have 25 in stock 17-June 2014.
73 (
pics and more info/items here).. ..also..below -- list of some good ones
here  that I sell (and I test my parts to be sure they work for u!)
I took a widely available (good) dg mosfet..the BF981 ..see pictures on this
page..and I soldered on some leads and created a good replacement for 3N211 or
40673 type DG MOSFET. If you want to see the
process go to this page.
I do custom repairs (FT301 mainly) but Argonauts 505- 515; some solid state Heathkit
items and accessories and I do custom creations ..such as these dg mosfets. Pictured
is my first effort (prototype). Worked very well!! Now to make it look pretty!!!
--- I do jobs like these on the bench at $10 per hour bench rate. RETIREMENT RATE!
MAIL ORDER JOBS! Older types of technology mainly that dont require service manuals
and specialized parts like PLL chips, LSI logic/cpus. Even some small mailable
consumer items I can do repairs by mail order...things like stereo preamps and certain
solid state amplifiers. I dont work with tube circuits all that much. my
email link is here
With a bit of thought
and planning and
soldering..I created a
good working ..rather
inexpensive
alternative to dual
gate mosfets such as
3N211 and the
discontinued RCA
40673.
The hardest part might
be locating wire for
the lead material. This
bare wire spool is a
tad thick ..but works
for the socket. I
bought it at Radio
Shack some time ago.
Below: pictures of my BF981 modification. I took one of these plentiful dual gate
mosfets and soldered some wires on the leads to make up a dual gate mosfet with
4 radial leads.

It worked well right off the bat. I have it in my FT301 front end circuit. I plan to make
some more of these up when time permits.
I have some 3N211s and will be selling
in small quantities for $7.50 ea plus
economy postage rate available.
House numbered Motorola (did a bit better than the 40823 or 40673) in front end of rcvr test
-- I still have about 6 available $3.75 each

3N201s Texas Instrument old stock - $3 (very soon I plan to test them in my rx front end
circuit for gain performance.. but for now..they test good on my DC tester

40673s tested $5.75 each (they work ok)
3N211s these are pretty good in front end of receiver testing -- $7.50 each
SFE1612 -- these seem to work best in rcvr front end testing I have done $5.75 ea (60 in stk)
I can test DG mosfets with this new transistor/FET tester I bought off
ebay about 8 months ago now.

What I do is I short the gates together and measure it as a JFET.

This is a basic DC test to ensure the device is OK.

Another thing I do with dual gate mosfets (from time to time) is I test
them in the receiver front end circuit of my FT301.

The FT301 has plug in circuit cards and the receiver front end board
unplugs rather easily and I have a transistor socket for the RF stage
(amplifer) and the mixer stage. Both stages are dual gate mosfets.

For a hotter receive/mixer I have substituted in SFE1612s for both the
mixer and the rf stage.

Want a socket for a transistor or DG mosfet (4 leads) I use Single in
line machined IC socket and I cut it to size - cut each pin off
individually and make a socket. I sell a strip of this socket material 40
pin for 85 cents each and I have about 50 strips in stock.

I use this stuff all the time to make sockets -------------------------------->>