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

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

On Sat, Apr 19, 2025 at 01:16 PM, Mark Lunday, WD4ELG wrote:

9 B Bioenno battery (

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Of all their batteries I found all of the "9V" were when full charged were

11.1Volts, not much surprize as there are no combination of LFE or Lion

that hits 9V they are all 11+ Volts or the next increment down 8.4 or 7.2V.

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Likely as the voltage drained off it settled some closer to your target.

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

VarAC software, Windows 10, triggers tx no steady output, rx perfect and have CAT control of frequency:

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I have chosen the QRP Labs QDX for CAT rig configuration (tried all sorts of Kenwood too). Baud 115200 (all work down to 9600), Parity none, DataBits 8, StopBits 1, DTR H and RTS L.? No default option like WSJTX.? Windows sound card sees QMX output and input. All 100% volume and WIndows identifies no problem. On the VARA sound card when tuning from 0% to 100% there is no actual tx, though the card shows tx.? If I initialise everything and test PTT on the VarAC settings,? 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.? I am in USB mode.?

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No issue with WSJTX digi setup.? I am familiar with the software and the truSDX works.

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Any advice appreciated!

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Well alrighty then!? I had NO IDEA that the voltages were that way, Stan.? I'll never understand why 9V is actually 11.1V and 12V is actually 13.8V LOL.? Thanks much.

Jamie, when I measured current draw through the QMX +5V PPT line connected to R6 with RF in, the values were quite high at up to ~150mA.? So I then tried injecting the +5V directly to the base of T1 (at D3 cathode end), the currents were more reasonable at no more than ~35 mA and usually quite a bit lower.? The QMX transmitted CW just fine through the amp and I was getting about 20W out on 20M into a dummy load (my QMX puts out ~4W in).? I could stop and start transmitting CW without problems.? I had installed the latest SSB firmware and have the PTT delay set to "50".? I have not played with this setting while injecting PTT-P after D3.?

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FYI, when I tried grounding D5, the current draw was also quite high, so I did not try PTT-N to this point.

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I think this is the best that can be done with my limited knowledge and without major changes to the WA3TFS circuitry.? I am going to hardwire in a TRS jack for connection to the QMX PTT-P output and test some more.

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Then I will test external MIC/PTT operation.? Portable SSB SOTA / POTA operation was my major reason for building the WA3TFS amp.

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73,
Jim - AE5JE

On Sat, Apr 19, 2025 at 01:16 PM, Mark Lunday, WD4ELG wrote:

with a freshly charged 9 B Bioenno battery

Mark, a freshly charged "9V" Bioenno battery will have an output voltage significantly higher than 9V.?

From the Bioenno manual, its nominal voltage is 9V, but its charge voltage is 11.1V.? After some amount of running discharge time, which decreases the 'full charge' value to the steady state value, quoting from the manual, "The battery outputs a steady voltage around 9.6V until very little capacity remain".

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So you were likely running your QMX at significantly higher than the recommended voltage for a 9V build.? If you run FT8 at this voltage level, it may result in damage to your finals.? CW and SSB may survive, but there is risk.? You should put a simple silicon diode in series in your data cable to drop the voltage by about 0.6V to be safe.

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I am not surprised that you had some problems; I'm not sure why a bunch of Factory Resets fixed it.

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Stan KC7XE

Yesterday I have just built this EFHW antenna for my QDX and in a few weeks my QCX+ 20M band to be built in May: using a HB9ZHK kit and 10 meters of wire (precisely cut for 14.060MHz with a SWR of 1.13:1). I will add a very tiny 150pF SMD C1 capacitor in parallel of the primary to improve ?its efficiency in higher frequencies. This antenna is just spread out of my 4th floor balcony using a 5 meter long telescopic fishing pole.?
Today the 150pF SMD capacitor was soldered (second photo). It was not an easy task for a 80 years old OM with eyesight his age and shaky hands! You can compare the size of C1 with the size of the BNC plug. I had then to cut 10cm of wire then 10cm again and finally 6cm more because the addition of C1 modified the antenna but it works well now giving a SWR of 1.3:1 at 14.066MHz then 1.1:1 at 19.733MHz and 1.9:1 at 27.066MHz. If I want to use it on other bands I will have to add several lengths of wire connected by gold plated banana plugs.

73-Pierre-FK8IH