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The Assembly manual clearly states that the PCB board is the heatsink, not the washer.

I've been using a self-built high band, 12v, QMX, in our Florida heat, for many months and have never felt it hot, or even warm to touch. NOT a problem!

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OTOH, I don't do .

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72 de N4REE, Bob Easton - QRP CW forever

I used this method as well, assemble the display, connecting pins and front panel using the top two screws with nut spacers. Solder just the front pins to the display.? Then disassemble and follow the instructions, except that the front pins with the poor access are done.

On Sat, Apr 19, 2025 at 08:27 PM, Stan Dye wrote:

I'm not sure why a bunch of Factory Resets fixed it.

Probably because the op fiddled long enough to draw the voltage down to an acceptable value.

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Y-O-Y did Han's waste so much time putting multiple LARGE PRINT, red font, voltage warnings in the manuals?? ;)

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72 de N4REE, Bob Easton - QRP CW forever

For information, with the Windows volume all 100% as well as the Vara sound card (change has no effect) my 20m VarAC output is 2.5W.? That is 1/2 of WSJTX output.

My approach was to use the method described in Hans' instructions for the 2 corner pins. That was enough to establish position. Then, I loosened the screws just enough to allow the assembly to tilt back about 1/4 inch. That gave enough room to make the rest easier ... and without letting the spacers escape.

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72 de N4REE, Bob Easton - QRP CW forever

I think you should buy some (maybe a box of ? ) transistors and a bigger heatsink and some plain board and read up and start from there?

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When messing with input stages ?you’ll find the input impedance all over the place (hence the pi attenuator input)

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When messing with output stages the dissipation will increase and the impedance varies with the point in the cycle (so the LPF action is degraded) and remember the 50W amp has never been wideband?

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Remember the interesting way Hans avoided RF feedback at switching points by boosting the switching diode bias from the RF waveform - that probably needs checking ?too

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The QRPLabs 10W linear amps and the 50W non linear amps seem to have very similar output circuitry. I am awaiting delivery of my QMX+ but I also have had for a long time one of the 10W linear amps (bought in anticipation of the QSX) that I want to use. My question is…if I removed the BS170 drivers in the 10W linear amp and added a smallish input matching attenuator would the gain be sufficiently reduced so it could be driven linearly from say a 1-2W drive from the QMX? I am really only interested in the SSB output at the higher frequencies i.e 10m and 6m and beyond, as I noticed reports of quite low powers reported generally from the QMX+ at these frequencies.

I was proposing feeding the output of the 10W amp back through the QMX+ LPFs as the old LPF modules were rated at 10W so I don’t see why the QMX+ should not handle the same. I was even considering changing the IRF PA devices for the higher frequency version used in the 5W amp (did this and got it working on 70MHz fine).

wadderya think?

73 Ken G4apb?

I’ve built two QMX+ and used this method to solder the display.

It adds probably 15 minutes to the build time, with the pre-assembly and disassembly, but so much easier to solder!

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Gotcha, thanks Jerry.

Nice article, but I see two problems...?

1) It will also attenuate received signal

2) If built into connector it vill be hot

On Sun, Apr 20, 2025 at 01:17 PM, Stan Dye wrote:

Make sure you have QMX SSB input set to 'USB' rather than 'Ext. mic'.

That is it Stan I now have tx power thank you!

Thanks Stan for your VarAC setup, I have replicated it, no change there is a momentary tx less than a second then nothing even when protection is disabled. To do it again I have to switch the QMX off and on again.? After replacing the BS170's that failed at the last band calibrating, I have not tried calibrating as I am weary it will fail again. Calibration may be an issue? Everything else works SSB voice tx and WSJTX.? Will sleep on it.

Oops, mis-spoke, the drive level is very important for VARA; I set it to max.

Make sure you have QMX SSB input set to 'USB' rather than 'Ext. mic'.

Stan

Not much different, I don't think.

- QRP-Labs QDX for PTT Config and Freq Control; works to set freq and PTT

- In the VARA modem settings (not sure if any of this is relevant):

VARA Modem souncard settings: select QMX devices.

The Drive level doesn't seem to do much on my setup for USB mode (rather than digi); the devices are set to 100% in the windows soundcard settings.

Thanks Stan, no S appears.? You have described your VARA setup elsewhere for WINLINK, please can you give it for VaraAC which has more detail to it?

On Sat, Apr 19, 2025 at 07:06 PM, Klint VK6KLI wrote:

I see a momentary full power on the QMX then immediately nothing and I have to switch the QMX off and on to repeat this.

This would happen if the QMX is going into SWR protect.? Does an 'S' appear after the frequency on the QMX display?

My VARA HF works OK with both VAR-AC and Winlink in USB mode.

Ludwig,

My apologies for not responding today, I was busy all day with a search and rescue exercise.

Anyways, I tried what you suggested and made sure that there was FT8 activity on the frequency and did not hear any difference.

Thank you,

Kai Bouwman

On Sat, Apr 19, 2025 at 05:54 PM, AE5JE - Jim wrote:

WA3TFS amp

For PTT operation remove C17 (or lift one leg)

5v injected into that point (R6) will cause it to go into TX and should

be under 3ma.

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C16 and C17 determine hold in time after release.? Fro SSb longer is ok.

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With C17 in you have the COR and that can be very troublesome for SSB TX.

As it can be sluggish and pop inand out while talking likely damaging the

finals in the QMX.

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Allison
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Allison
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