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Cell phone signal amplifiers pengyou The Tech Zone 26 07-14-2018 05:48 PM

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Old 02-21-2019, 07:38 PM
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Default Amplifiers for HF



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I see amplifiers that are very expensive. I was wondering if there was a kit (good one, not chinese ebay junk) that could be had for a reasonable price?

Or even a basic DIY project where you source parts, and build from scratch.

Todays markets are flooded with all in one prefabbed and prebuilt. I wanna make mine, but would love if anyone here has personal experience with kits or DIY designs.

Thanks in advance,
CPLS.
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Old 02-21-2019, 07:44 PM
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I would avoid the Chinese amps ..

But RM Italy has quite a selection.

I am going to get one of their 10,11,12 meter amps.

http://www.rmitaly.us/

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Old 02-22-2019, 05:50 AM
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Are you looking for solid state or tubes? Plenty of designs around for tube type amps that aren't hard to build. Tube amps lend themselves to point to point wiring. Most solid state amps are FET output stages and can have stability problems. They are best built on PCBs.
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Old 02-22-2019, 09:27 AM
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I personally do not care, but after getting an old tube CB, tubes would work for me. I am only 33, so I missed the tube years. But building, from what I have seen, was easier then (size of components and no surface mounts.)

Franklin, if you have any links to a nice tube amp, please post. I'll look around, but for future reference. If I find one, I may do a build thread to, well, probably embarrass myself.
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Old 02-22-2019, 11:51 AM
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http://www.w6pql.com/
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Old 02-22-2019, 12:23 PM
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Quote:
Originally Posted by CPLSeraphim View Post
I personally do not care, but after getting an old tube CB, tubes would work for me. I am only 33, so I missed the tube years. But building, from what I have seen, was easier then (size of components and no surface mounts.)

Franklin, if you have any links to a nice tube amp, please post. I'll look around, but for future reference. If I find one, I may do a build thread to, well, probably embarrass myself.
A number of tube projects in ARRL books. I'll go through them and see what I'd recommend. Back in college we had to design and build a 40 W tube amplifier for one of the labs. Wish I saved that. A home built tube amp is much easier to test and align than a solid state amp.

I plan to design my own solid state amp once I retire but that a couple years away. I'm slowly acquiring the transistors. Right now I'm designing my own 40M AM radio. All SMD. I'm building it in modules.
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Old 02-22-2019, 01:07 PM
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Quote:
Originally Posted by CPLSeraphim View Post
I personally do not care, but after getting an old tube CB, tubes would work for me. I am only 33, so I missed the tube years. But building, from what I have seen, was easier then (size of components and no surface mounts.)
Tubes are getting harder and harder to find. Also the support gear for tubes is getting harder to acquire. For example, tube sockets, chimneys, transformers in the right voltage ranges, etc.

With that said, if you are willing to do the tube thing, look at ARRL handbooks from the 1950's, 60's, 70's, and early 1980's (some of those can be found online in PDF form). While home brew tube amps still showed up in the ARRL handbook until well past those dates, the construction practices used from the early 80's back might be more easily duplicated. For example, hand winding coils instead of trying to find a specific manufactured air core wire inductor. Each year handbook typically has three or more home brew HF amplifier designs, from moderate, mid, to high power. Depending on the year of the handbook these might be in the HF Transmitting chapter or they may be in separate Amplifier chapters. Some amplifiers carry over year to year for several years, so if you grab a handbook from every 3 or 4 years you would end up with a dozen or so amplifier designs to pursue.

And yes, in my opinion tube amplifiers are easier to build because of the flexible construction possibilities.

Handbooks from the late 70's on up are good places to look at home brew solid state HF amplifier designs, including techniques to cut the required PC boards.

Regardless, some of the parts will be hard to get today, and you will end up substituting parts, but that is OK, you absolutely can do so if you consider your substitutes carefully.

I have home brewed amps from 2 Watts up to legal limit (as well as transmitters, receivers, and ancillary gear). My first HF transmitter was home brew, and I used it for well over a year with my original Novice station. I have helped others in similar projects. It can be fun and rewarding, but also a bit frustrating depending on your electronics background.

T!
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Old 02-22-2019, 02:02 PM
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Quote:
Originally Posted by CPLSeraphim View Post
I see amplifiers that are very expensive. I was wondering if there was a kit (good one, not chinese ebay junk) that could be had for a reasonable price?

Or even a basic DIY project where you source parts, and build from scratch.
Ask yourself some questions to help define your project.

- What will you be driving this amplifier with? Amps driven from QRP transmitters are very different from amps driven by 100 Watt class transmitters.

- What bands do you want to operate in? Of course, for an HF amp, it is tempting and easy to say "all of the HF bands". And that is very doable. However reducing to a single band or maybe two-three bands (properly selected) can reduce the complexity of the amplifier by removing band switching components. Sure, it only reduces complexity a little bit, maybe 10-15%, and reduces usability a lot, but for a first project that simplicity can be the difference between completing the project or not.

- What power level do you want? This is closely tied to the "what will you be driving the amplifier with" question, but lets assume you will be using a 100 Watt class transmitter. Building a legal limit amplifier means you need about 13+ dB of gain (easily done), but the tubes get pretty pricey and you really need to have 240 VAC in the ham shack. Sure, you can do legal limit from a 115 VAC outlet, but that is not optimal at all, 240 VAC is much preferred. Building a 400-600 Watt amplifier is much easier, it has lower gain (more forgiving of construction practices), is smaller (generally smaller tubes and much smaller power supplies), is cheaper (can use less expensive, more readily available, lower power tubes like 572Bs or 811As), and runs easily on a standard 115 VAC outlet. And the real world power difference between a 600 Watt signal and a 1500 Watt signal is certainly there, but pretty small, a little over 3 dB, or a bit over half an S unit.

- What modes will you be operating? An amp designed for primarily SSB requires less overhead than one that will see a lot of CW, AM, or digital modes. Those other modes can keep average power high for extended periods, requiring greater cooling.

There are other questions you have to answer before you can start to select an amp to build, but I think at a minimum you have to answer the above before anyone can realistically suggest something that might work out for you. And depending on your answers, there could be further questions.

T!
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Old 02-22-2019, 07:45 PM
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I would invest the time, energy and money into improving your antenna system before buying an amp. Back during Desert Storm deloyed personnel didn't have Satphones, etc. like they do now. So we ran hundreds of phone patches, often having several ships in rotation, relaying between the sandbox and the states from an installation near Washington, DC. We almost never needed to "put the log on the fire," but most of the time had phone patch quality running "barefoot," about 80 watts PEP using the exciter only on the Harris.

BIG difference was that we had a huge Sabre Log Periodic Dipole Array, using sections of Rohn 45 tower for the boom, having a rotator about the size of a VW engine with the antenna elevated about 100 ft. and fed with 1" Andrews Heliax air dielectric feedline. Your tax dollars buy the very best.

Humorous note, some fishermen on different boats started rag chewing just outside the amateur portion of 20 meters and were encroaching onto the band edges allocated for military use. We had two ships in rotation running patches and needed to ask them to change frequency. The bottles in the Harris amp were kept warm so that it was always ready in case we needed the extra horsepower. Flipping a few switches the exciter awakened the amp to full military power, which is several times that permitted in the amateur service. That got the fishermen's attention.

One asked the other, "Who was THAT?, the FCC??" "No!" the otherstation said. "I think it was GOD!"
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Old 02-23-2019, 08:45 AM
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If you watch Ebay and Hamtrader there are quite a few Heathkit SB200 amps that have been completely rebuilt that show up in the $400-$600 range. Bullet proof amp and EMP proof as well (if that is a concern). Yes they wont do some of the newer bands such as 15 and 17 meters, but a great amp none the less and far better than any Chinese built.
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Old 02-28-2019, 07:39 AM
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Thank you guys for all the great advice. I am looking at a 100W transmitter (ICOM IC701 is my main rig) and looking to do 500ish Watts, SSB, and at least 80 and 40M. Perhaps 20 as well. Definately want to stick with 110V, as I have no 220 in my house except for my dryer. I do wish that I lived in the day of the builders. I guess more because there were more knowledgable people everywhere to learn from. Nowadays, you almost have to learn from online and such. I just didn't even know where to look for the information to guide me. I would love to build my station from scratch, from the transceiver on up. I will be looking into the older books for the information to learn how to build an amplifier. Part of the reason to build as well is I can justify buying parts over time. The XYL might get mad if I spent 600 at once, but 800 over time she would not notice as much. Tell me you don't know what I am talking about.

Thank you guys again.
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Old 02-28-2019, 10:35 AM
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Here's an article from QST in the 1960s about a table-top 10-80m 500W amplifier using two 811A tubes.

RF Parts has 811As in stock, to include matched pairs for reasonable prices.

Note, it is not trivial to build an HF amplifier, and it can be dangerous. The plans above assume the builder has a certain level of understanding and experience adjusting and working with critical components of the amplifier circuit. Also, don't assume the plans are correct as published. It would be a good idea to see if QST published any errata for this article.
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Old 02-28-2019, 09:06 PM
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Thank you for that. Yes, I must admit, I am no expert in electronics building from scratch, but have at least started working on kits. I do have a local elmer, who fixed my old radio, that can at least give me a hand in doing a like project.

I am aware of the dangers, as I am very cautious with electricity. I appreciate the article. I just didn't know where to look to start studying for a build.
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Old 02-28-2019, 09:27 PM
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I think it would be cool to build an amp using the envelope extraction / restoration method.

Basically you have a powerful class C amp modulated by another amplifier that restores the amplitude component. The phase and frequency are amplified in the class C PA and the amplitude is detected and reapplied as a DC supply.

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Old 03-01-2019, 06:38 AM
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Quote:
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I think it would be cool to build an amp using the envelope extraction / restoration method.

Basically you have a powerful class C amp modulated by another amplifier that restores the amplitude component. The phase and frequency are amplified in the class C PA and the amplitude is detected and reapplied as a DC supply.

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The big problem most people have when they start building projects from published circuit diagrams is how and where to layout the circuit. Not uncommon to find you boxed yourself in and have to start over.

I suggest checking out Bob Heil's pineboard project.

https://heilsound.com/amateur-radio-...board-project/

Can get you some experience with tubes, small project, can find pictures of builds on line to help you with layout.

It's tempting to look at larger projects when you start out but you really have to work your way up.

Here is an HF amp project a guy on QRZ is developing.
https://forums.qrz.com/index.php?thr...lifier.646433/

Once he gets it complete he may have some extra boards or share the PCB artwork. He is designing on 100mm square board so he can order for China at very low cost.
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Old 03-04-2019, 01:09 PM
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Here is a 20W HF amp kit. I just found this and haven't given it a good review but these types of builds are great for starters.
https://www.qsl.net/k5bcq/Kits/Kits.html
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Old 03-05-2019, 05:32 AM
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Related QRZ thread that might interest those interested in building HF amps. Actually a number of related discussions in the homebrew section.

https://forums.qrz.com/index.php?thr...inners.588719/
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Old 03-07-2019, 11:26 AM
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Thanks for the links and information... the K5BCQ kits seems like they could be very interesting little projects.
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Old 03-07-2019, 02:41 PM
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ARRL has some good books on radio circuits.

The Amplifiers book has some interesting circuits. Mainly tube oriented.

Experimental Methods in RF Design is a more advanced book but well worth studying.

Valve Amps Explained is coming out later this month. From the description it looks interesting. I'll need to add that to my library.

If you want to learn about radios in general, Build Your Own Transistor Radios is another good book.
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Old 03-07-2019, 03:47 PM
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I just bought a 1200W amplifier. Tube style. May need some basic fixes, but at least I have a guy who can go over it with me. I made an offer, and the seller accepted. More that I was looking for, but again, the guy is not a ham. Gamble? Yes, Either way, almost guarenteed to be fixable. The tubes still glow and appears to function. I'll get back to you guys on it when I find out more.
Thank you for your time.
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