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Amplifier suggestions for the QMX+

 

Hi,
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I'm looking for amplifier recommendations to boost the signal on my QMX+. It doesn't have to be more than 10W or so. I have considered the QRP Labs 10W amplifier, but I think it needs a band pass filter for each band? I'm not an expert on amplification.
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The chinese have some offerings for QRP transceivers - I understand one of them is not that good ( the 50W HF Power Amplifier for USDX) but are any of the other ones worth a look?
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Any recommendations or other tips? THX!
 

Arne,
A 10W amplifier will give you only about 1/3 of an S unit at the receiving station, not a lot of help. I would go for 20-50w. My research has found several that claim to be linear, i.e. usable across multiple bands.?
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  • The WA2EBY is a build it yourself amplifier. 1w in, up to 40w out. It is a1999 design by WA2EBY produces a multi-band amplifier using push-pull MOSFETs and a multiband Low Pass output filter. Two QST articles give extensive design and build details. Requires 28v power supply for full output, but can operate with 13.8v supply at reduced (unspecified) output. Find a kit at:
  • The WA3TFS amplifier can be obtained already built and with 5w in offers 20w out. HOWEVER>>>> The amp provides space for ONLY ONE LP filter, and is therefore a single band amplifier. See the Assembly Manual for filter details. If purchasing, order for the band you want to use. Find it at:
  • The K9HZ 20W Power Amplifier (PA) is a class AB2 HF amplifier intended for open source and homebrew transceivers such as the T41-EP SDT v12. With an input of 0dBM (1mW) and 12V DC, this amplifier produces 16W RMS continuously or 20W PEP in HF bands 160M-6M. The RD16HHF1 transistor finals are used quite conservatively, higher output powers are possible with minor adjustment (at the cost of reduced duty cycle). I have not done enough research to know if this amp also requires a LP filter following. Available in kit form at:
None of these are plug-n-play, multi band amplifiers. I do not own any of these and am currently undecided, but would like to hear from people wh o have used any of them ... or found a better solution.
--
72 de N4REE, Bob Easton - QRP CW forever
 

AC9YY is using a Mercury 3S and getting 400 watts out on SSB with his QMX+
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--
John AE5X
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Correction,? 300 watts
--
John AE5X
 

Hardrock-50 is a great amp. ?Combined with my Smart Power Attenuator (SPA), they make a great driver for a linear. Shameless plug:
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73,
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Robert, WA2T
 

Hi,
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The QCX+ has less than 5 watts output on the high bands. This limits the available options.?
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?It does seem to have more punch with CESSB.
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If you invest in a better antenna, like a HexBeam that seems like a best option until QRP Labs offers a matching amp. Then you have better directional gain, lower noise than a vertical and it can be mounted as low as 10-15 feet.?
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Anyway you have time in this Sunspot cycle, as
on good days running barefoot with CESSB, may actually be what Hans said....like 10 watts. So far the reports have been excellent.?
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72,
George
K3GK
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The Hardrock-50 plus ATU kits.
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And I re-worked my HR-50 into the HR-50+ 100 watt amplifier.
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Good kits, well-done build instructions, and enjoyable to build (especially if you like winding toroids, which I do).? And first-rate customer support.
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Either the HR-50 or HR-50+ can be driven to full output on a couple of watts of drive.? I built my QMX+ as a 12VDC so as to be able to crank its input voltage way down to manage output power.
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- Bruce K1FFX
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I have used Micro PA-50+ for a couple of years. Chinese amp. Uses RF to detect band and PTT so no QMX connection other than RF. Reliable 50 watt out, but needs SWR less than 2. Price about $180 (at least was before tariffs.?
John?


On Fri, May 2, 2025 at 8:48?AM Bruce K1FFX via <rosen.bruce=[email protected]> wrote:
The Hardrock-50 plus ATU kits.
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And I re-worked my HR-50 into the HR-50+ 100 watt amplifier.
?
Good kits, well-done build instructions, and enjoyable to build (especially if you like winding toroids, which I do).? And first-rate customer support.
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Either the HR-50 or HR-50+ can be driven to full output on a couple of watts of drive.? I built my QMX+ as a 12VDC so as to be able to crank its input voltage way down to manage output power.
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- Bruce K1FFX
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QMX+ not QCX +.?
 

Bruce, I went to Hardrock. Are they only producing assembled amps now??
 

On Fri, May 2, 2025 at 10:07 AM, john terry wrote:
Uses RF to detect band and PTT
Using detected RF for TX/RX switching will always present a high VSWR (open circuit) to the radio while the RX/TX switching (and in this case, LPF selection) is occurring.? A few milliseconds is plenty to blow a semiconductor device.? MUCH better to use a wired PTT if at all possible.
73, Don N2VGU
 

Thanks,
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these are all very helpful tips! I have a lot to learn, that is clear.
 

People like the micro PA50+, particularly after upgrading to the latest firmware. As mentioned, using?wired PTT might be safer than RF sense. The PA50+ does have some ACC output, and I believe people have reported getting it working for PTT with e.g. a QDX, but I don't know the details. There is also a recently released micro PA100 that got pretty good reviews.

I have an MX-P50m which is manual band switch and wired PTT only. It works nicely with my QDX. I did make the modification to improve the PTT input buffering.

Spectrally both of these are reported to be decent, but may be borderline?on some bands.

On Fri, May 2, 2025 at 7:35?AM SA6ZGM Arne via <ak.vikhagen=[email protected]> wrote:
Thanks,
?
these are all very helpful tips! I have a lot to learn, that is clear.

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