Hi Francesco,
Have you used a nanovna to sweep the gain and input impedance?
You'll need a 1:1 input transformer (unbalanced to balanced).
You'll also need an attenuator on? the nanovna TX output to reduce
the level, I'd suggest something like 20 dB so the loop amp isn't
being overloaded. If you sweep it please post the results.
73,
Steve AA7U
On 1/2/2025 11:55 AM, Francesco Caizzi
via groups.io wrote:
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Good morning, I'm wondering if anyone like me has made a full
working Wellbrook 1530 LN amplifier based on the schematic found
in the files section named "Wellbrook_Loops.Kicad_sch." with smd
2SK932 jfets (but others schematics are very similar) I'm asking
because I made a couple of them over time, one even with the
original 2SK715 jfets but in the end they have the same problem,
that is, they seem completely deaf up on LW and MW to the
shortwave range, where they work much better...a classic
amplifier with only two transistors (BFU590QX) works regularly.
I tested the jfets (taken from the European electronics
e-commerce portal TME) and they are all ok, the absorption is
normal at about 115 mA at 12V. The toroid windings are the ones
described on the schematic: input P3/S12 (plus the two single
turns) secondary with crossed wires - output P9/S5. Test loop
hang from a tree in my garden at about 2 mt. from ground.? I'm
adding the link with a short video and I've put two photos of
the boards so you can see the construction. Thanks in advance,
F.
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