(tr)uSDX Forum

Because it is hard to make QSO‘s on SSB with 4W I was thinking about building an external power amp without spending more than the (tr)uSDX.

https://m.nl.aliexpress.com/item/32808409970.html

https://m.nl.aliexpress.com/item/32741570452.html

Anyone already used those? I can find some positive blogpost’s from people who used this amp on a FT 817. Also with additional LPF.

Thank you for your comments

73 de PD5ANT

Hello PD5ANT,

I have used both the MX-P50M and the Aliexpress Minipa 70 with the (tr)usdx and had great success. After adding the amps, I can work any CQ call I can tune in. Over past weeks I’ve logged over 65 Parks on the Air QSOs across the US and Canada from the west coast of USA. I’ve even logged QSOs with Moscow, Czech Repuplic and Italy.

Don’t get me wrong 5 amps gets heard, but I wasn’t breaking through on longer range pile ups. No problem now.

Similar performance from both Amps and the Minipa only costs 20 USD and you get to build it.

73
KA6VPJ

Hi KA6VPJ,

Thank you for your info! I will order and build the MiniAmp and give feedback on this forum.

You are also using a filter, any recommendations?

73,
PD5ANT

KA6VPJ
Was the kaisaya the one that you built?

Hello Anton

The low pass filter that you see in the picture is set up for 20M. I purchased the board from ebay. The board also comes with T50-6 toroids. You just need to add magnet wire and capacitors.

Here's the link seller. He's super responsive and ships same day. 3.99 USD for the board and toroids.
ebay.com/itm/Low-Pass-Filter-Circuit-Board-T50-6-Toroids-HF/195298546974

I have second board on order for 40 meters. i plan to stuff both boards in a tin case and add SMA connectors to quickly change bands. I'll add pics in a few days once i built the second board.

73
KA6VPJ

KA6VPJ thanks for the info! Been looking at this also and was wondering about where to get a filter that works with it.

Cheers

Thanks again KA6VPJ!

This seller will not send to my country but I will find an alternative.

First things first; wait for the amp kit.

73,
Anton

Hi KA6VPJ,

Do you have the dimensions of the PCB (from the 70W miniamp), than I can look for a matching heat sink.

73,
PD5ANT - Anton

100 x 50 mm exactly.

Hello Anton,

The heat sink I purchased off Amazon was 100 x 69 x 36. In retrospect, a heat sink that large was probably not necessary. It won’t hurt, either.

By the way, if you are planning to use it for CW or digital, then the 50w amplifier kit from QRP Labs is a better option. It kit includes a low pass filter and heat sink. Unlike the MiniPa70, the PPT feature should also work with the (Tr) uSDX unmodified. However it’s not recommended for SSB. This is why I’ve never paired my QRP Labs Amp with my (Tr) uSDX just my QCX mini.
https://qrp-labs.com/50wpa.html

Lastly I recommend putting the MiniPa70 in an enclosure. The solder pads are very delicate and lift easy. I’ve also snapped off the SMA connectors. Attached below is the MiniPa70 in its new enclosure.

73
KA6VPJ

In case it hasn't been made clear, using a band-tailored LPF on any of these DIY Ali / ebay amps is NOT optional. Sure, it should work just fine, but you'll be in major violation of regs for spurious emissions.

At least in FCC territory, the loudest spur must be at least 43dB below carrier.. which I believe translates to 1/20,000th of carrier power?

Hi guys!

I just ordered Minipa 70w. Will use it with (tr)uSDX, classical configuration 80-40-20-15-10.

Should I made 5 different LPF for each frequency ? Maybe there are switchable LPF for whole bunch of classical frequencies set ? Does anybody have schemes ?


Best regards,
73! Dmitry.

I describe the issue and a working PTT driver in another thread viewtopic.php?p=4751#p4751

Dmitry,

I have an HFpacker amp that I use when needed. The amps are no longer available, but most of the build files can be found at https://groups.io/g/hfprojects. The amp has a fairly small 10 band switched LPF module that might work for the AliExpress amp. The last time I looked Virgil K5OOR was still active on the group and answers questions about troubleshooting the amp.

73 Mike

Thanks Mike for HFProject. I found schemas for LPF filters there.

Further research lead me to http://tonnesoftware.com/
There is a collection of free software for LPF design and analysis.

Hi KA6VPJ,

Almost finished my MiniPA70, BPF and PTT circuit.

Do you use an attenuator between the (tr)uSDX and the MiniAmp? I’m afraid on 20m a have 5-6 watt as input for the MiniPA.

73,
Anton

Hello Anton,

I use 2x 18650 batteries to power the (tr)usdx when i use the amp. This allows me drive the amp with around 2.5 to 3 watts. I get 45-50 watts out of both the minipa 70 and the Mx-p50m. i have never blown a transistor and have about 50 SSB QSOs on each.

Build and tested, really happy with the results. I have no tools to measure the output but it is a lot easier to make a QSO.
Using with a manual switch for optional extra power.
No problem with 12v on the (tr)uSDX and the MiniPA. First test was with a 6v lead battery (~1,5w output power). Because the SWR behind the MiniPA is not as good as direct on the antenna (4:1) I tried 12v and this seems to be a good combination.

73,
Anton

Hi Anton,
Could you please elaborate on the SWR topic? I just ran a test with the QRP Labs 10W linear PA and had a horrible SWR of around 8 when using the PA. I wasn't sure if I made a mistake when soldering the PA or if the trusdx didn't like the QRP Labs PA...

73!
Simon

Hello Simon,

I have no experience with the QRP Labs amp. The HF MiniAmp - EFLW has a fair SWR <2 after retuning my antenna.

This weekend I blew the FETs from my Amp because the coax wire came loose from the PCB. After replacing the FETs I will make a 40mtr bandpass filter and check the performance on this band.

73,
Anton

AntonR wrote: ↑01 Dec 2022, 07:15 Hello Simon,

I have no experience with the QRP Labs amp. The HF MiniAmp - EFLW has a fair SWR <2 after retuning my antenna.

This weekend I blew the FETs from my Amp because the coax wire came loose from the PCB. After replacing the FETs I will make a 40mtr bandpass filter and check the performance on this band.

73,
Anton

Thank you, I solved the mystery. I was simply overdriving the QRP Labs PA as is only needs a few mW drive Last weekend I soldered the AliExpress 70W amp together but for some reason I only get 20W out. It never gets boring...

I have been looking at this thread carefully as I now have a 2E0 licence so I can transmit up to 50W, and like others here I've found it a bit hard to get through pile-ups with 5W. Does the kit from Ali such as this have the surface-mounted components already installed or do you have to solder them yourself? https://www.aliexpress.com/item/1005002 ... arzE6TUKGE

I see in the photo that you are using a PTT mic. How do you like it with the truSDX? Did you try any others?

BrumasterM01 wrote: ↑28 Aug 2022, 20:12 Hello Anton

The low pass filter that you see in the picture is set up for 20M. I purchased the board from ebay. The board also comes with T50-6 toroids. You just need to add magnet wire and capacitors.

Here's the link seller. He's super responsive and ships same day. 3.99 USD for the board and toroids.
ebay.com/itm/Low-Pass-Filter-Circuit-Board-T50-6-Toroids-HF/195298546974

I have second board on order for 40 meters. i plan to stuff both boards in a tin case and add SMA connectors to quickly change bands. I'll add pics in a few days once i built the second board.

73
KA6VPJ

Congratulations friend, great tips, does this PA work on all bands, requiring only the change of the filter according to the band?