[Elecraft] Re: K3 6m pre-amp

[Jan Erik Holm]

Or BF981 would work nicely. However don´t know how hard to
get they are these days.
A preamp with NF below 1 can easily be built with a BF981,
forexample the YU1AW cavity design with BF981.

73 Jim SM2EKM
-------------------------

Jack Colson wrote:
> I personally would use a MGF-1302.
> 
> 73
> Jack, W3TMZ
> 
> ----- Original Message ----- From: "Jack Smith" 
> <jack.smith at cliftonlaboratories.com>
> To: <w3fpr at arrl.net>
> Cc: <elecraft at mailman.qth.net>
> Sent: Wednesday, July 30, 2008 6:48 PM
> Subject: Re: [Elecraft] Re: K3 6m pre-amp
> 
> 
>> 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