I was just too arrogant! Turned the QMX on and all good.........I thought. Great 4 for 4, QCX+ 50W amp andQDX all built and working plus the QMX.
Too good to be true. Yes it turns on and all the menus work. Checked the diagnostic, yep, all good. Listened to the phones, hmmm, just background noise, no signal. Plugged in a signal gen -105dBm, nothing.
Checked the audio graph and all the red and yellow dots are at the top of the graph. *** !!
Some serious rewinding to do, BUT, my snips have gone missing which is odd because there's? only me and the XYL here! I would run the QDX but there's? a very large thunderstorm here so looks like beer o'clock!
Have a great weekend all.
73s



--
Phill EA5JHA

Number of turns are exactly as per the assembly manual. I spread out the turns a bit more evenly but this yielded only very minor improvements. TX power on 15m went from 1.9W to 2.0W (@12V). Anyway, at least it’s working now.

73,

Andreas

Thank you Hans.? I knew that you would increase my level of understanding.? ?The student defers to the master,? again, lol.? Can't wait to get mine on the air.? 72, Doug?

I find with W11 if I plug the USB lead in to the radio and computer and then turn on the QMX it will be Ok. ?Otherwise as you say W11 usually reports a malfunction.

That was cya for us.? I am interested in hearing why you don't? include one.? Is there a reason?

Here is my zener protection test video:

I use 47V 1W zeners on my QDX and QMX. No issues no mosfet smoke!

--
?

73, Barb

Hi Larry, could you provide more details about this circuit? I tried it but it didn't work.

Tie the output of the regulator to amplifier PTT (5V active high)
Connect the gnd pin of the regulator to the PTT circuit of the rig.?
So when the PTT provides a ground to the regulator, it switches on, and 5V is used to activate the 50W amp.

I understand the on/key-down state here. But what about the off/key-up state? IIUC, when the rig is in off/key-up sate, the ground pin of 78L05 is floating and I believe in that case, the output and the ground pin will both see a voltage at about 1V less than the input voltage. In the attached picture below, pin1 is Vout, pin 2 in Gnd, and pin 3 is Vin. The inner pin of the DC ?connector is at about 11.6V. With pin 2 floating, I measured 10.6V at both pin 1 and pin2 which means if pin1 is connected to the 50W amp's active high PTT, the amp will always be in the TX state. Did I missing something?

73 de Zhenxing N6HAN

No replies yet on the specs for this capacitor.? This is in a low pass filter, so it will see some voltage.??

Based on the markings, this is a Vishay/BC capacitor.??

On Digikey, I see a 50V 5% NPO through-hole 2.5mm spacing that looks similar. No minimum order and less than 6 USD for 3-day shipping to correct my mishap.
https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/K681J15C0GF53L2/2823740

My only question is whether or not 50V is enough for this application.

Any idea what voltage the lowest frequency LPF might see?

Mark
W8GU

I’ve successfully updated my qmx software, but WSJTX does not find the qmx audio files for input and output. When I plug in the USB-C cable windows says USB device not recognized. I have QMX in digital mode as manual says. What am I missing?

On Sat, Jun 8, 2024 at 06:22 AM, David Wilcox K8WPE wrote:

Another issue I have discovered is that the wires on some caps and resistors are NOT copper wire tin plated.

The leads are likely Kovar? or Alloy 42?, which are used in semiconductor packaging due to their low coefficient of thermal expansion and the ability to be wet by glass seals, which makes them compatible with other packaging materials e.g. alumina oxide ceramics and plastics..??
They are alloys of nickel, iron, (and cobalt in Kovar), thus are magnetic.??
They are not used because they are cheap, they are used to solve packaging problems.
73, Don N2VGU

开云体育

Alison, Bruce,

NO and no.

The transformers are completely unsuitable for 2M.? For 2M I've had best result
using coaxial Transmission lines of the correct impedance (not 50 ohm!)

The IRF510s are untried at 2M.? Highest I've gone with them is 70mhz
and then it was pushing a bit. At 2M the input match requires a considerably
different approach and mosfets that will work there.? Forget a simple
transformer.? There I've used both TLT and stripline matching.

For 2M I'd start with RD series for 12V operation or MRF101 or MRF301 at
(50V).? Then a much different board and likely switching.

--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.

They are VHF FETS but the transformers (cores etc )will be way out of their comfort zone, the gain well down from HF levels etc. ?

The PCB might be a basis for your own ?VHF design but there will be a lot of experimental design to do ?

Hi all,

I realise that this is way out of it’s specification, but does anyone have any experience of using this amplifier on 2m?

I’m not expecting 50W but will it work at all?

73/72
John
M0JBA

I bought the Hakko FX888D before starting on these kits. ?Also, a spool of Kester .015” lead core solder. ?When I read Jeff Moore’s suggestion sheet it stated a recommendation of 790 deg F. ?This seemed high, but it works perfectly for me with these boards. ?Also pushing down “hard” and the solder point for good heat transfer is essential.

73 Todd K4MSW

In preparation for building my own mid-band QMX, I was rewatching Hans' "52 tips for building your QMX successfully!" video. Interestingly, if you go to the 30 second point in the video and look at the upper left-hand corner of the QMX board he is holding, you can see that the inductor is damaged similarly to yours. Assuming that is a functioning radio, I would take that as tacit acknowledgement that the radio can still function with that kind of damage.?

Danny
Great amp. Have been using mine for 15yrs with FLEX1500, now replaced with QMX HB.
There is a mod to set the input power to 5W or 10W. With the QMX (9V) running at 8V
there is enough drive to realize full 50W out on bands 20 thru 10.?
GL de Barry