[Elecraft] Re: K3 6m pre-amp

[Jack Smith]

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

Don Wilhelm wrote:
> Bob,
>
> While I cannot speak from my own measurements, but in EMRFD, Wes 
> Hayward recommends the U310s for VHF/UHF rather than the J310.  The 
> case of the U310 is connected to the gate, and when used in a grounded 
> gate configuration, the case can be mounted (upside down) into a hole 
> in the PC board, and I believe that alone should provide better input 
> to output isolation.  The Vishay data sheet indicates a slightly lower 
> noise figure for the U310.
>
> I would suggest that you try the J310s.  If you find them lacking, it 
> should be easy to change to U310s, I would guess that at 50 MHz, it 
> may be a 'toss-up' decision.
>
> 73,
> Don W3FPR
>
> Bob Tellefsen wrote:
>> Hi John
>> I've been looking at this circuit for some time.
>> I have a number of J310s, but no U310s.
>> Do you know whether they are the same
>> animal, just in different casings?
>> 73, Bob N6WG
>>  
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