QRP Labs 50W PA: 3 things you should know before buying

[@Inkling777]

Thanks for the review. I'm old enough to remember the Heathkit era of ham radio. My first SW radio, an inexpensive GR-91, came from that Benton Harbor company. More and more I've come to believe that Hans Summers has made QRP-Labs into a one-man Heathkit. What he has created is amazing.-WA4MP

[@Linas_LY2H]

Thanks for a comment Michael! I fully agree on Hans-Heathkit parallel! He's the only one , IMO, among the ham radio gear producers, making really cheap and really quality products ! These two features very rearly go together :). Great shoutout to Hans! 73! Linas LY2H

[@sAsDoCToR]

Thx for infos, i use this PA with QDX and work great but only for 20mt band, i add also 2 x 40mm fan with a 3d printed support, no trouble no much hot and work like a rock.

[@chrisherd991]

Hi Linus. Thank you. I have one ready to build. I will build it on 20m and use a separate 40m LPF in series with the output for 40m. I also plan to use the 18V lipo battery from my portable drill as the power supply. As always thank you for the tips.

[@Linas_LY2H]

Cool! It will actually work on 30m too with 20m LPF, as does 20m QCX :) 73! Linas LY2H

[@bill-2018]

Hans has some nice products. Years ago we needed bifilar wire when I worked in engineering and the drill was our solution. We did lengths of about six feet and a piece of paxolin with a screw through the centre to put in the chuck and two holes either side for the wires to be knotted, this way the wires were held securely and tension put on. I keep looking at p.a. circuits to make an RD006HHF-1 amplifier for all h.f. bands. G4GHB.

[@Linas_LY2H]

Hello G4GHB! I very glad my favourite drill method is used among the proffessionals internationally! Good luck with construction of your own HF amp, let us know how is it going! 73! Linas LY2H

[@bill-2018]

@@Linas_LY2H Bifilar wires must be some 45 years ago. I've got the mosfets resistors, ferrites, BPF, some capacitors needed. Waiting for a radio rally, none yet. 73, G4GHB.

[@rst5nn]

Thank you for video. I have an idea to get this PA and supply it by Type-C PD using trigger for 20v from powerbank. That is why very interesting current consumption with 20v. But if it uses 80W and output after converter is about 20v it is about 4A? Not sure there is such powerbank, it will be simpler to assemble from LiIon 26600 5s pack.

[@Linas_LY2H]

Thanks for watching! The power draw at 21V was ~6A DC to produce 45W RF from this PA in my experiment video. So, it is 126W of DC power needed, whatever way you get it from. Good luck! 73! LY2H

[@rst5nn]

@@Linas_LY2H Linas, many thanks for answering. Maybe you remember name of you dc-dc up converter? It seems like this is a simplest way to get 20v from my 6A LiFePO4 4s battery.

[@Linas_LY2H]

@@rst5nn You’re welcome! I don’t know the name of my booster, except that it’s “DC/DC step-up converter from 10-32V to 12-35V”. I bought it at my local electronics shop. Here is the link to it to see the description : www.anodas.lt/dc-dc-itampos-keitiklis-is-8-5v-48v-i-10-50v-10a-250w-step-up?search=dc%2Fdc%20step-up This converter is of Constant Voltage/Constant Current type which is not necessary for just a power supply. I am using it also as a solar charge controller and/or a battery charger where you need to regulate the current, not only the voltage. You may find a great variety of just voltage-regulated step-up converters on most internet trade platforms. HTH, 73! Linas LY2H

[@WB0RLJ]

Hello, Linas! I just finished building my QRP Labs 50W Amp. Curious if you implemented the mod that is recommended on the top of page 66 of the build manual? I didn't notice that recommendation until I got to the setup and operation section. Other than that mod, everything seems to be working on my new build! 73, Jim WB0RLJ

[@Linas_LY2H]

@@WB0RLJ Congratulations Jim! Hope, it’s gonna work and work bringing numerous DX into your log! If you mean the mod to the QCX-mini transceiver ( that’s what I could find on page 66), then no, I don’t have the 10k resistor installed accross the pins 13-14 on the IC3 chip, as I bought my QCX-mini factory-assembled. But I’m sure it’s a very good mod and I would consider it if I were using my QCX-mini with the amp often. 73! Linas LY2H

[@brambo4776]

Love those little rigs!!

[@johnpeterson7264]

Great review, very informative !

[@warplanner8852]

The winding method for the two transformers is very good but do not despair of you don't have one of those marvelous old hand drills. A power drill with a variable speed will work well if done carefully. And, actually, the trifilar transformer is easier to mount because of the hole placement.

[@Linas_LY2H]

Sure, but be careful with the power drill,- you can make a mess in a second :) 73! Linas LY2H

[@TheFretman2]

Nice video!

[@paulmetzger7428]

Wish I could use it with my Elecraft K1, but don't believe I have a PTT trigger line out from the K1 to tickle this amp.

[@mightmike8312]

You can use the 6R line from the k1 as the PTT

[@Linas_LY2H]

thanks for an input! 73! Linas LY2H

[@TheShawna1]

Ive bought one of these to use with my QMX on 40 meters.J just have to figure out the PTT 5 volt thing... I hear the QMX gives keying problems with this amp but there are some work arounds i've been hearing of, one is a resistor in parallel with 210 in the QMX which allows a full 5volts for the PTT ring line? I may do this to my QMX.jim KB1PFL

[@Linas_LY2H]

@@TheShawna1 Hello Jim! Thanks for sharing your experience! Unfortunately, I don't have this PA anymore, so I'm not able to test it with my QMX radio , but it seems to me that as it comes to the 5V PTT line , both QCX and QMX provide for a similar way of switching. In the QMX, you can, actually, choose in the menu what kind of PTT system you need: "pin-to-ground" on transmit, or a "5V-to-pin" on transmit. In my QMX , both work ok- I measure 5V on the ring contact on the PTT socket, or I can get my microPA-50!amplifier keyed which needs a ptt-to-ground on the tip contact of the PTT jack, if I choose so in the menu. As I said, I can have "full" 5V on the QMX PTT ring contact no problem, but I haven't tried it to practically key the PA50 to make sure these 5V is doing their job :), if this was your question... So, if I were you, I would first measure my QMX if I have 5V on the ring contact of the PTT jack during the transmit ( after activating this option in the menu), then , if 5 V is ok, I would just connect a cable to the PA's PTT line and see if it all works. The only problem I know -there is a factory mistake left in PCB tracks , so you need a tiny jumper wire to install between the two contacts of the PTT jack to fix this. This is very well described on the QMX webpage on the QRPLabs site. HTH, 73! Linas LY2H

[@ai5dd]

You keyer sounds weird, like it's sending micro dots (if that was your key), also I must have had some skip on 10 meters, I was using the FT-818 set to 5 watts and I made two DX QSOs to Japan and Croatia from north central Oklahoma (U.S.). I'm still waiting for my QRP Labs QMX assembled radio. 72/73 de AI5DD I like how you send PSE at the end of your CQ, I may start doing that :)

[@migalito1955]

Very interesting especially at a price of roughly 30 USA dollars. If it handled SSB I would be ordering one today & I may none the less. I harvest transformers out of old audio equipment and by adding rectifiers and voltage regulators turn them into power supplies to match my needs, so the required voltage does not put me off at all, although your scheme of using a DC to DC boost converter is equally a good solution. Good to hear Ukrainian HAMs are getting back on the air & I can only hope their country kicks out with prejudice the Putin invaders. As a matter of fact my Ham equipment had been in storage for several years and I just recently brought it, which is now only two QRP transceivers, out of storage and put up a nice 40 meter inverted V antenna in the hopes of hearing traffic from Ukraine and surrounding countries. Thanks for the review & demo... 73 from kc2wvb in the NY Catskill mountains.....

[@Linas_LY2H]

Thanks for watching! Congratulations with getting back on the air! The PA could probably handle the SSB traffic but then you need to play with the bias current levels of the transistors for the linearity and purity if signal sake. It could be a bit complicated as Hans only left one variable resistor to regulate the current in both transistors as his goal was simplicity, not linearity (you don't need linearity in CW anyway) :) Nevertheless , the user manual reads you still can do it but there you are on your own! So good luck and let us know what were your results! 73! Linas LY2H

[@migalito1955]

@@Linas_LY2H Thanks, I may give it go now nowing that in theory linearity is possible & at worst I am out $30. I do have some friends that are very skilled EE's, where sadly I am not one since I went the M route found in the acroynm STEM.

[@Linas_LY2H]

@@migalito1955 If you are major in M, you can do everything ! CU on the air!

[@migalito1955]

@@Linas_LY2H Well I wish.... Theorectical math at the graduate level gives you a lot, but not everything plus the darn EE's confuse me when they use linear mathematics to model what clearly is not such as the relations involving bipolar transistors and fail to mention they are using an aproximation to overcome the difficulty imposed by the nonlinear relstions involved. That once threw me for a loop for several hours until it dawned on me what they were doing. 😃 Plus I really need to take the time to be better able to analyise small signal AC circuits especially when it comes to estimating source & load impedances which are very important to be aware of. If I were not 68 I'd probably go back to school again.....

[@Linas_LY2H]

Hmm… Things might get complicated and they will, accordingly to the Murphy’s laws. But the good news is the User and Assembly manuals are so well written by Hans that it only takes to follow the script step-by-step carefully and success is guaranteed! Especially tat this PA has got no SMD parts, all through-hole and is fun to assemble! 73! Linas LY2H

[@brianfields4479]

how many watts did you use from the qcx mini to the pa ?

[@Linas_LY2H]

I used as many W as my QCX-mini has, -5W :). The built-in 3dB attenuator on the input makes the PA safe from overdriving. But even with attenuator, I would not recommend putting in more than 6W as the final transistors of the PA could be damaged. 73! Linas LY2H

[@Porco_Utah]

I only do CW, so no need for linear amplifier, non linear amplifier are more efficient , IRF 510 cost less than US$1 each AG6JU

[@Linas_LY2H]

I agree with you. CW makes life so much simpler! 73! Linas LY2H