![Homebrew amplifiers for qrp transceivers Homebrew amplifiers for qrp transceivers](/uploads/1/2/5/6/125641734/608963431.jpg)
MX-P50A hf power amplifier for QRP transceivers. Can be used both as a base and mobile unit, Extremely Small Compact and light weight, Full integration.
I've been looking at amps for boosting a QRP transceiver up to the 100 W level. (Yes, I already have a 100W transceiver, but hey, if I had a KX3 and an amp, maybe I wouldn't need one The elecraft KXPA100 sets the upper range at $700 for a 100 W HF solid state amp. Slightly less would be the Hardrock 50 at $300 for 50W and the HF-Packer around $300 for 35W. Then there are the CCI Motorola app note amps starting under $150, but they aren't complete kits and have a bit of a bad reputation. I loved the Kenwood TS 520 SE that I started my ham radio career with and I never minded tuning up when I changed bands (which I do fairly rarely) so I got to thinking about a tube amp for going from 5W to 100W. It seems like most of the homebrew tube amp designs I deal in units of kilowatts, so I am looking for suggestions for building a much more modest tube amp. Would the dual 6146s of the Kenwood still be a good choice?
Are there other tubes that might be appropriate for this power level that would be durable and abundant? Where does one get the uniquely tube components like HV transformers and plate chokes and so on?
Most of my junk box comes from old CBs, so I don't have a good selection of relevant parts for hollow state projects. What do you think of the idea of trying to build a homebrew tube amp to compete with the largely solid state offerings in this power range? Is this a reasonable and cost-effective design choice, or are there reasons that the above transistor designs are a better choice? Thanks in advance for answering the questions of a tube newbie.
I built the HF-Packer for a friend around 10 years ago. It's not necessarily a kit for the beginner, but went together pretty easily. However, I thought the one I built was more in the range of 85 watts, not 35 watts. But that was 10 years ago and memory being what it is.
Anyway, it did work well. The friend I built it for still uses it with his FT-817. A tube amplifier could certainly be built but it would be clumsier than a transistor amp. You might want to purchase some of the older ARRL handbooks from the 70's. I always see older handbooks for sale at every hamfest I go to.
You could also hunt through some of the old QST or 73 magazines. QST requires membership to get at all the old copies, but all of the 73 issues are on line. The designs from the 70's were often meant for the Novice operator, which were limited to 75 watts. They were usually CW transmitters and biased Class C, but could be modified to use them as a linear amplifier with lower output power. There is also some of the old Heathkit designs. My Heathkit HX-1681 CW only transmitter is a hybrid and uses a tube output amplifier. The amp contains a 12BY7 driver and two 6146s, has about 100 watts output, and is biased Class AB2.
This transmitter was commonly hacked by CBers for a linear. If you can find one at a hamfest, you would have all the parts you need except for the power supply.
The power supplies are usually easy to find on EBay. I would recommend you consider a pair of 811 tubes as the basis of a new amplifier. At 100 watts output they should last a long time. To get enough drive you will need a buffer stage and band switching that goes along with this type of design. Final plate voltage won't need to be more than about 1700 volts. I have a single 811 Linear now that was built for 6 meters all self contained.
The 811/572 are triodes so need no screen supply. You should also consider some harmonic filtering in any design you chose. I feel overall, these tubes would be the best overall selection for the long term and for reliability, with plenty of head room for power between 160 m and 10 m.
Once finished and all issues worked out you will be proud of it for a long time.
Most of my QRP operating is portable; sometimes just in the back yard. But my home QTH does have a ham shack with a 100-watt transceiver so I have the option to move to more power.
Not everyone has that. So if you sometimes wish you had just a little more 'oomf' in your signal, this is a US$24.00 'semi-kit' 40-watt amplifier with the board and some parts; you get to buy the rest of the parts yourself. Looks like it comes with the PC board, the final transistors and low pass filters. 1w in gets 40-w out.
I'm thinking about putting one in my motor home so all I have to do is tote the K2. If anyone builds this, it would be interesting to hear about it. « Last Edit: June 04, 2016, 10:56:24 AM by K7EXJ » Logged. Again the stupidity of buying a Small 5 watt Dick Tracy radio and then adding a filthy solid state amp because 5 watts is inadequate most of the time for reliable communications. We have so many QRP 5 watt stations bragging about how easy it is even on SSB yet they buying filthy CB amplifiers or poorly designed Ebay PA's to make their 5 watt radios more powerful. After decades of research the military have concluded that 20 to 30 watts of output in a portable radio is all that is needed using a wide variety of antennas. I wonder why hams sometimes think that they know better, but I guess the sales of these crap amplifiers prove that 5 watts is mostly an impractical power level especially on SSB for reliable communications that is not short skip in nature or within ones own continent or country.
Manufacturers need to stop fooling hams with these toy radios and start building decent portable or portable radios. QRP radios should be built 25 to 30 watt clean PA's You can operate with 25 watts with lithium battery packs very easily. 25 to 30 watts will drive most amplifiers to 400 or 500 watts of output. For dxpeditions and portable with or without PA 25 watts can make successful contacts without relying on super stations hearing you. There was even a 50 watt Portable HF Radio made called the QMAC HF90. These radios can be seen across all continents being used both portable and in a fixed station role by the likes of the UN and Red Cross. Theres some reviews on Eham.
This is the direction ham portable HF radios should be going rather than the big mess of unreliable boxes and cables and worst inadequate output power. Manufacturers need to stop fooling hams with these toy radios and start building decent portable or portable radios.
QRP radios should be built 25 to 30 watt clean PA's You can operate with 25 watts with lithium battery packs very easily. 25 to 30 watts will drive most amplifiers to 400 or 500 watts of output. For dxpeditions and portable with or without PA 25 watts can make successful contacts without relying on super stations hearing you. There was even a 50 watt Portable HF Radio made called the QMAC HF90. These radios can be seen across all continents being used both portable and in a fixed station role by the likes of the UN and Red Cross. Theres some reviews on Eham. This is the direction ham portable HF radios should be going rather than the big mess of unreliable boxes and cables and worst inadequate output power.
There have been several radios sold that put out 20-25 watts. But they are no longer in production. Among them was the Vertex VX-1210, SGC-2020 plus several 10 meter mobile radios HTX-10, HTX-100, HR-2510, HR-2600.
The FT-897 ran 20 watts on battery power. One of the currently made Chinese radios puts out 20 watts. Unfortunately the Xiegu X108G reviews have not been good. First the EBAY design is only the board set that can also be had from FARCircuits.
Look up the WA2EBY/K5OOR articles (two) QST March and april of 1999 for the whole story. It requires 24-28V to develop full power (much more than 25W more like 40-45) and when built right and not over driven its clean enough.
As to QRP rigs and clean PA, what is the point again? Most are CW and clean is harmonics being adequately down. For most of the SSB radios they sound good and the few I've tested (other than my designs) were clean enough.
Why a power amp rather than building in 20W, weight and power. IF the rig is optimized for 20W the efficiency of a SSB linear is inefficient at 5W. Higher power requires heavier devices with higher standing bias to be linear even at low power. A matched external power amp is easy to shed and at zero efficiency cost (other than battery weight and amp weight). It also allows scaling to 100 or more watts. As to having a hard life making contacts with SSB at 5W, I've used my FT817, Argonaut 505, and three home brew (HF) SSB radios for years and a good resonant antenna (EF halfwave) up high has kept me in QSOs. And when it didn't the 100W radio was often only marginally better (conditions!).
Usually I go to another band at that point. Then again with 160 pounds of NiCd battery I can run 100W for a FD weekend. If I have to do that with under 10 pounds of battery its 5W as even 20W is too much. Point being running a crappy antenna and high power is OK when that antenna is all that is possible works, but efficient, not! Starting with an effective and efficient antenna will have a better chance from the start. Why waste 7-10db on a loop or 12ft loaded antenna on 40 then make it up with 40-100W unless that is the only choice.
I hear it now the small antenna is lighter and easy, however the bigger battery and added amp are not lighter in any way and never mind wires and cables. The other scene is those that run at home with the same QRP rig, added power is not a weight burden nor is wires and weight. Still if you getting more power its still better to have a efficient antenna.
Often then its space, cost or the reality that its really a hobby that has limitations for most people. For those what you got has to serve many roles. For field day we ran VE7CA (QST November 2001) Triband (40-20-10) two element wire beams and the result was for the next year we built two more so each station (phone CW and digi) could have one. It proved 5db of gain was significant at QRP and 100W level. Consider that.
FYI its an easy build and works well. Allison Logged. Manufacturers need to stop fooling hams with these toy radios and start building decent portable or portable radios. QRP radios should be built 25 to 30 watt clean PA's You can operate with 25 watts with lithium battery packs very easily. 25 to 30 watts will drive most amplifiers to 400 or 500 watts of output. For dxpeditions and portable with or without PA 25 watts can make successful contacts without relying on super stations hearing you.
There was even a 50 watt Portable HF Radio made called the QMAC HF90. These radios can be seen across all continents being used both portable and in a fixed station role by the likes of the UN and Red Cross. Theres some reviews on Eham. This is the direction ham portable HF radios should be going rather than the big mess of unreliable boxes and cables and worst inadequate output power. Apparently Zenki has not been able to find Menu 75 on the Yaesu FT-857D. Or has yet to realise that at 30 watts, the interference caused at -30dB IMD levels is the same as a legal limit setup with -47dB IMD levels. Come on man, I buy into your clean PA argument but the lack of logic here is just stupid.
Of all the groups to lecture about trashing the bands. And whats this rubbish about 20 watts being fine for Military and the UN, but only 6dB!!! Less is useless, even for amateurs?!!! Let the QRPers have their QRP-PAs I say. I've got a nice little band pass filtered Chinese made one good for 30 clean watts @ -30dB. Makes for a nice cute little shack on the picnic table! I used to think Zenki made some good points, but this thread has made me think twice about ever paying attention again.
« Last Edit: June 30, 2016, 03:51:35 AM by VK3BL » Logged.