I recently bought a so a preamp for my receving loops for SDR and pocket radio. I had the need to move the antenna away (out) of my listening post without affecting the receiving performance and went for this preamp for a few bucks.
It arrived very fast, but a first test, I suspected a DoA. The preamp has a neat relay arrangement that moves it out of the way of the receiver when not powered on, connecting in and out directly. But once powered on, nothing, no signal. So I started digging around and found that it could be similar to this preamp which is in turn a variation of w7iuv preamp. So I took note of the bias current and make a mental note to measure it and some voltage and make sure that the preamp stage was indeed alive.
That’s when I noticed I had a missing jumper. I supposed this was intended for bias current monitoring and a quick google image search confirmed a jumper is supposed to be there in normal operation. I measured the current flowing in this branch and seemed to me a reasonable bias current for the transistor….
So I added it and my receiver finally came alive
I wonder how many are sent back for an issue simple as placing a jumper on two contacts. It now works very well. By the time I figured this out, many people would just place this in the ‘lost hope’ basket.
Profit