Linear amplifier build

[Elf36]

I was curious why you don't hear much about people building linear amplifiers? Yes, I know some people do, but it seems like it would be more common, especially since they're so expensive to buy. There are lot's of skilled builders out there,  I have built a few QRP kits and other easy kit's. I don't consider myself to be an electronics wiz, I just know how to solder and follow directions. Does anyone know of any amplifier kits that are decent and don't cost a fortune (100/200 watt HF or VHF) ? Any info on the topic would be appreciated. Thanks

[RobRich]

These days the popular kits seem to be larger solid-state amps. The Mercury III kit is quite popular, but it is a modern 1200w LDMOS amp kit costing ~$2500.

Scaling down, the Hardrock-50 comes to mind. Around 50w on HF with 5w input. A little less on 6m. Around $350 to $400 for the kit, though.

There are several inexpensive "Chineseium" 25w-50w kits floating around Amazon, eBay, etc. Expect poor to even no real documentation, though guides by actual kit builders should be available.  The bigger problem is the tendency to have no output filtering. Usually not even a basic lowpass filter, a huge YMMV putting a potential "splatter box" on the air without adding the cost and time to build a filter network. Then there is the potentially questionable IMD even if filtering is applied.

Perhaps a better bet for what you are seeking would be a starting with a monoband homebrew HF tube amp from the multitude of project guides from over the years. It could be later scaled to multi-band. The GI-7B tube used to be popular for homebrew amps up to a few hundred watts, but I am not sure anymore. Perhaps even more affordable and readily available would be like a couple of 811a tubes in grounded-grid running say 200-300 watts PEP.

[ThaDood]

Sounds like you'd like what they talk about on 3885AM, 7290AM, and if you can ever catch 'em on AM in the 160M band, like around 1885kHz. (All +/- 12kHz.) A lot of those dudes are runnin' homebrew linears, some capable of 2kW, or more. And, not just HF, but Tuesday after on 7290AM I heard about a 2M SSB freak whom built his own 2M 2kW linear amp. And, if you go on there to QSO and ask these dudes about what they build, most of them are more than glad to share that info with ya. I've yet to do this, since my linear is an Ameritron AL-811A amp, that I bought from a silent key's family estate sale. Question is, when ever I wanna' attempt to do DIY linear amp building, do I want to go 'old school' tubes, or paralleled MOSFET's? Oh yeah... With F2 propagation coming back, 29.0000MHz AM in 10M is another FREQ to listen for that talk, +/-20kHz.

[RobRich]

*Tube amps tend to be more forgiving for building, but they also incur the usual high voltage dangers.

The affordability and ready supply of components for modern 50v+ solid-state amps is compelling IMO.

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Curious, Dood regarding your amp, are you still running 811a tubes or has the swap for 572b tubes been done?

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Some of the big-iron stuff on 160/80 can be multiple KW, or as often stated, "legal limit with headroom." Rest assured some of those ops are running them as such, too.

[Elf36]

Yeah. I guess all in all building one isn't that cheap and might require more skill than I have. I suppose if it were cheap and easy, it would be much more common. On the high voltage side of things, I had a large Linear amplifier my grandparents bought at a garage sale. Don't remember what model or wattage etc, but it's been almost 30 years and I sure remember taking off the cover and getting shocked by it. I've been shocked a lot in my line of work and I still remember it very well. I can still see those tubes glowing! Thanks for your responses.

[RobRich]

If seriously wanting to try building, look into a low-power CW transmitter kit. Most of the output-stage principles are the same. It is just at a much smaller scale.

You can obtain a Pixie kit for like $15 shipped at eBay or similar. It is mostly just soldering it together, but you will get an idea about the circuit design. Being a low-power CW rig, you also do not have much concern about extensive filtering, IMD, etc. As you already likely know, 1w CW on 40m with decent propagation can work considerable distances.

After that maybe look at an intermediate kit like the QRP Labs QCX+ 5w CW transceiver. Around $55. The two surface-mount ICs are mounted already. The rest are through-hole and similar components.

https://qrp-labs.com/qcxp.html

BTW, about forget. QRP Labs has a neat affordable 50w CW monoband amp kit, too. Uses a couple of IRF510 transmitters. Even has proper lowpass filtering.

https://qrp-labs.com/50wpa.html

[Elf36]

I've built two or three PFR-3 transceivers, CW/Pico keyers, Regan receivers, etc. I would like to start building more. I enjoy it when I have time.
https://www.qrpkits.com/pfr3.html

Just never done anything more complicated that involved unfamiliar components. I'm willing to learn though

I have actually been teaching my son to solder the last couple of nights. I brought home a printed circuit board and some diodes we don't use anymore. Tomorrow I'm ordering an Elenco FM radio kit to build with him. It's only $14.99 and the manual teaches you about different components and what their function is as you go along. Looking forward to that... I think. I'll get to show him how to use a multimeter for testing also. Hoping to drag him away from his PC and gaming system. So far he's done well with the soldering. Nice shiny hot joints!

[RobRich]

^ :cool:

An intermediate to advanced project could be something like a GS-35B homebrew amp. There are plans and even a site or two dedicated to it. As noted earlier, you could even start it as a monobander to simplify initial building, then later go multiband if desired. You would be looking at an 1000w-1200w+ HF amp for a few hundred dollars, or maybe even less if you can source a decent transformer from a hamfest, surplus, or similar. The tube with cooler still can be sourced from Eastern Europe for around $150 to $200. The downside is the socket and chimney might cost ya' as much or more than the tube.

[ThaDood]

Hey Robrich:    Boomer let me know that ya asked if I did a tube swap, yet, in my AL-811A amp to 572's. Um, no... At least, not yet. The only time that I've used the amp is doing AM stuff with the ricebox, in this case, the Kenwood TS-2000X. And, that's only on 75M, thus far. I could do 1885kHz AM, now that I have a Windom that's dead-nuts 1.1:1, I might try down there. By Timtron, WA1HLR, he recommends me running no more that a 90W carrier on AM using 811A finals. Why not 572's, yet? The $$$$ always goes someplace else. Ya know how that is. I did run into a great deal on a Xiegu G90 SDR rig, with 5W carrier on AM Mode, and plan to make-up T/R switch and ALC cables for that. 5W there into the AL-811A amp should still be over 30W out carrier. So, on quiet nights on 75M, that would work fine on AM mode, since I was running barefoot on AM for years before, with 20W, or less. BTW, speaking of the Xiegu G90, did ya see what they want for the accessory 100W brick for that? It's more than the rig itself. (Uh...)   

[Stretchyman]

Plenty of the BLF188XR linears around at reasonable cost think I got mine from RU for <£400, anything else (unless it's a newer device) is fairly pants and a waste of time.

Using a linear is a very poor way of generating RF power unless for SSB, if you're using A.M. class E/D is very easy to knock up and very efficient.

Depends what your trying to do!

Could you give us more info?

Regards.

Stretchy.