[Elecraft] Re: K3 6m pre-amp

[Jack Smith]

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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