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How important is gate capacitance? https://www.ti.com/product/JFE2140?bm-verify From https://www.ti.com/lit/ds/symlink/jfe2140.pdf Low input capacitance: 13 pF at VDS = 5 V ? High gate-to-drain

The TI JFA2140 is a matched pair of JFETs on a single die. No need to test and select. Rick N6RK

I should have said that the amp is a Wellbrook ALA1530LN. ?Everett

Steve, Thanks! Yes, that is an "R", not a "k" on the trimmer on closer inspection! -- =================================================================== Mike M

Martin, Comparing your schematic to Steve's I see a few differences: * The secondary of T2 is directly connected to ground in Steve's and through capacitors in yours. * 1.2k to ground at the

If anyone is interested I have a Wellbrook ALA1530 clone for sale. It is built with SMD JFETs. You can contact me off list if interested. everettsharp (at ) aol com. ?Everett N4CY

Here is a sweep of the preamp+BPF+16:1 input transformer /g/loopantennas/photo/296346/3807965 I might play a bit with the inductors and try to improve the pass band at around 3MHz,

I asked Andrew Ikin one time if he could share what core he used in his preamps for the transformers. He told me he uses the Fair-Rite 2873000302, same as I've shown on my schematic. (Amidon

The following photos have been uploaded to the Caaarlo LZ1AQ sweep ( /g/loopantennas/album?id=296346 ) photo album of the [email protected] group. *

Hi Martin,

Martin, just a remark, in your wire numbering scheme of the input transformer two wires of different windings carry the same number "4". Regards Fred

I found another JFET matching circuit at: https://stompville.co.uk/?p=112 It is slightly more complicated but would be easier to use.

Martin, on your schematic you've got the resistor feeding the 2 x 1N4148s as 500K, whereas Steve has it at 1K. Should it have been 500R? Mike -

Thank you. I should note that my group opened and traced out 3 different ALA1530LNs and all had a single 82 pF cap across the two loop inputs. Apparently you had a variation if yours had two 82 pF?

The phasing dots of the transformer are a key piece of information in the circuit diagram and crucial for proper functioning of the amplifier. regards Fred

Hi Mike, Yes, it appears your numbering matches with the proper phasing of the one-turn feedbacks. But RV1 is 100 ohms ("100R"), not 100 k ohms. That pot is set so both Source sides are the same

On the off chance there is interest in matching JFETs for a clone of the Wellbrook loop antenna, I've posted a PDF of a simple and effective unit. Layout isn't critical, I constructed mine on

Mine added too, derived separately, useful for comparison purposes. /g/loopantennas/photo/267767/3807916

Steve, Schematic added: /g/loopantennas/files/Wellbrook%20T1/schematic.pdf Also, I notice that the 2SK715 had four ranks for IDSS and the 2SK932 has two ranks for IDSS.? Any idea

Hi Mike, One would need a full schematic with the T1 transformer labeled per your drawing to be able to say if you have it correct or not. My schematic in the files doesn't have transformer numbering