I'm using J310 parts in a VLF-LF-MF-HF active antenna design I'm working
on, no need to go to the U310 version at those frequencies.
I've found best intermodulaton performance in the active antenna
requires 25 - 35 mA idle current with 8-10 volts source-drain, so
there's some advantage in rated dissipation with the U310 part.
Another used-to-be-common part is a 2.5 mH RF choke, pi wound on a
ceramic form. After a lengthy search, I found Hammond still makes these,
only to learn that they were discontinued earlier this year. I managed
to get one (at a price of $14) and it's good that I only needed one to
use as a comparison reference for a QEX article I'm working on.
Jack
Don Wilhelm wrote:
Jack,
I understand the vanishing part syndrome. I have a few remaining in
my parts bin, and I am not about to give them up (similar feelings
about my dual gate MOSFETs).
As an alternative to the U310, when laying out a PC board (or
Manhatten construction board), one might consider the SMD version of
the J310/U310. It should be at least as good as the U310 and likely
better. A nice clean layout is critical to performance in a VHF/UHF
amplifier. A carrier board may be needed for Manhatten construction,
but for 3 legged devices, a carrier board is simplicity itself - just
a tiny scrap of rectangular PC board with the copper cut in half along
the length and one of the remaining long rectangles cut in half across
its width. Caution - cut the copper on the corner of a larger piece
of PC board and then cut out the result as the 'final act' -
attempting to cut through the copper on a tiny board can result in
injury to the fingers and hands. With the demise of thru-hole parts
and the advent af inexpensive SMD parts, we hams will have to learn
how to deal with these tiny devices if we are to continue homebrewing
and experimenting efforts at a reasonable price.
73,
Don W3FPR
Jack Smith wrote:
Don:
The U310's are not too easy to find these days. Vishay seems to be
the most common (only?) new production supplier and the one-off price
is about $14 from Mouser or Arrow. Digikey, Allied and Newark only
stock the SOT23 plastic surface mount version. TO-92 plastic case
parts, the J310, are around 25 cents each. The U310 and J310 are
supposed to have the same die, so differences should be attributed to
the case, but who knows what goes inside the package these days,
particularly if it is from China.
If I were building a pre-amp based upon a U310, I would start with a
J310 and get it thoroughly debugged before experimenting with U310's
at $14 a pop.
It's something like the 40673 dual gate FET - once ubiquitous and now
difficult to find and expensive when found.
Jack K8ZOA
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