Building an Amp

[RunAway15]

So I thought about trying to build an amp myself. I've been seeing a lot on the forums about how easy it is to build or copy a smaller amp, but whether someone actually knows their stuff will show in the bigger stuff. If that's true or not I have no idea, but I think I could twist together a keying circuit and tie some 16ga teflon around some chokes like they are supposed to be, and I know how to use a multimeter and solder pretty good.. I actually have a DVD with pictures and instructions and a parts list that Lou Franklin sent me years ago on how to build a 2 pill. And plenty of building videos on line. But I'm no tech. Anyway, I think I could copy and paste an amp together, but I don't have any equipment for testing or tuning such as bird meters or scopes and the fancy stuff. I have a basic Astatic 5000 watt meter, a multi tester, and a soldering station. That's about it other than plenty of hand tools and such. So here's my question, for those that have built amps before; suppose you're stranded, locked in a garage with just the bare minimum in tools, such as I mentioned, could you build an amp that you could use to get a signal out? I want to learn, but want to know if I am even in the position to consider buying a kit or something and see if I can get it to work. Another question is if I don't have the bare essentials then what would those be? And how do you tune an amp after its built? I've seen no pots to turn. Lol.. Now, I will brace myself for the scourging and mockery I will have to endure for being a noob and just putting myself out there like this, but if it can help me get to where I want to be before I have to once again leave this place with you guys and go back to the world of working adults raising kids and making a living then it will be well worth it.. Thanks in advance..

 

[nomadradio]

There are lot of things you can build yourself. Cars, motorcycles, aircraft come to mind.

Gaining your first experience building an amplifier would suggest a need for comprehensive and detailed instructions.

The more of them you have already built, the less you'll rely on those instructions. After the first dozen or so you probably only need to buy the parts.

But a first project calls for guidance. The more of it, the better. Don't know of anyone offering that.

And just how much related experience you already have is a big part of the picture. To acquire basic skills, a simpler project or two is a good place to start. Adafruit Industries https://www.adafruit.com/ or Sparkfun https://www.sparkfun.com/ and Jameco http://www.jameco.com/c/Electronic-Kits-Projects.html all sell basic skill-building type electronic kits.

But hey, even if it doesn't work when it's built, it's still a learning experience, right?

73

 

[RunAway15]

Anything else?

 

[sp5it]

What measurement equipment do you have? Do you have scope, signal generator, spectrum analyser and knowledge how to use those?
MIke

 

[LeapFrog]

What measurement equipment do you have? Do you have scope, signal generator, spectrum analyser and knowledge how to use those?
MIke

I think most builders started with a volt/ohm meter, and the old watt meter.

 

[RunAway15]

I think most builders started with a volt/ohm meter, and the old watt meter.

I have those. Will that get me started? If I can get it put together and see that it works I can send it it somewhere and get it checked and tuned.

 

[LeapFrog]

I have those. Will that get me started? If I can get it put together and see that it works I can send it it somewhere and get it checked and tuned.

If you find reasonable construction plans, (and depending on your skill level) I believe you will be able to build an amp that "works", but the input/output tune and capacitance values on the transformers may have to be fine-tuned by an experienced builder.

I don't know where most of the comp builders started, but I dare to say they got there feet off the ground without a spectrum analyzer or oscilloscope.

 

[RunAway15]

If you find reasonable construction plans, (and depending on your skill level) I believe you will be able to build an amp that "works", but the input/output tune and capacitance values on the transformers may have to be fine-tuned by an experienced builder.

I don't know where most of the comp builders started, but I dare to say they got there feet off the ground without a spectrum analyzer or oscilloscope.

I think I've found some decent plans. But how does one tune the input/output and capacitance values on the transformers? I mean I'm sure I can't. Was just wondering..

 

[n8fgb]

LDMOS

 

[RunAway15]

LDMOS

?????

 

[LeapFrog]

I think I've found some decent plans. But how does one tune the input/output and capacitance values on the transformers? I mean I'm sure I can't. Was just wondering..

By purchasing and using trimmer capacitors of the appropriate range. Just where you stick the trimmer caps is something that a builder will have to tell you because I honestly don't know. But I have seen them on top of the Transformers.

After the appropriate capacitance is discovered the builder will measure and replace the trimmer with a regular and permanent capacitor, but not always. If you hear someone say: "I mic'ed that in" there are talking about removing the trimmer capacitor and installing a "silver dipped mica".
Sometimes the trimmers are left inside, I imagine that can become costly.

LDMOS is in reference to the new mosfet technology made popular by nxp. (blf188xr)
There are boards available for purchase on eBay and the device requires a 50 volt power supply.

 

[Mudduckmobile]

?????

http://www.qsl.net/kf8od/
Look at the 8th item at bottom of the page under " Links to my projects",
then look at all the rest....There are other places too. I like this one.

 

[RunAway15]

http://www.qsl.net/kf8od/
Look at the 8th item at bottom of the page under " Links to my projects",
then look at all the rest....There are other places too. I like this one.

Sweet. Thanks..

 

[Crusher]

A couple of meters, so you can watch input vswr and output power at same time. Few extra watts on output isn't worth it if input starts to go up. Also need a power supply with a current meter and voltage meter. This will help when tuning if doing the math, you can figure out efficiency. ( this will let you know if doing crazy watts but not pulling current that it should be or if it's pulling to hard). You will need an assortment of trimmers. 1 for input, 1 across input transformer, one across output transformer and 1 for output tune. A scope is nice especially dual channel so you can compare input signal to output signal. When first keying, start with a low carrier/ dead key. Turn the mic Gain way down. Don't want a bunch of swing till you have it half way turned up. On the input transformer, you may or may not need a trimmer capacitor. Depends on device. Remember, most plans involve Toshiba transistors. The HG 2879 is a different animal and will not tune the same as the plans. I could go on and on. You will need a decent capacitance meter with some degree of accuracy. Otherwise you'll be putting fixed parts in that aren't correct. You will need a dummy load. Tuning on the antenna will cause false reading. When building 2 device homebrew amplifier, you will need to use right ferrite material on transformers. If not, things heat up quicker and may not match up as well. 43, 61&67 are common ferrite materials. I've said enough.

As to LDMOS, if he doesn't understand tuning. How do you expect him to understand bias or bias set point or how to do active biasing/ ( bias only only when keyed and grounded when in standby). If anyone has done one and it doesn't have thermal tracking. Watch what it pulls current wise until device cools down while in standby. Not to mention want bias applied before actual Drive is supplied. So some kind of sequencer is needed. Or footpedal, no keying circuit.

Ok, this 11meter junkie on standby.

 

[RunAway15]

A couple of meters, so you can watch input vswr and output power at same time. Few extra watts on output isn't worth it if input starts to go up. Also need a power supply with a current meter and voltage meter. This will help when tuning if doing the math, you can figure out efficiency. ( this will let you know if doing crazy watts but not pulling current that it should be or if it's pulling to hard). You will need an assortment of trimmers. 1 for input, 1 across input transformer, one across output transformer and 1 for output tune. A scope is nice especially dual channel so you can compare input signal to output signal. When first keying, start with a low carrier/ dead key. Turn the mic Gain way down. Don't want a bunch of swing till you have it half way turned up. On the input transformer, you may or may not need a trimmer capacitor. Depends on device. Remember, most plans involve Toshiba transistors. The HG 2879 is a different animal and will not tune the same as the plans. I could go on and on. You will need a decent capacitance meter with some degree of accuracy. Otherwise you'll be putting fixed parts in that aren't correct. You will need a dummy load. Tuning on the antenna will cause false reading. When building 2 device homebrew amplifier, you will need to use right ferrite material on transformers. If not, things heat up quicker and may not match up as well. 43, 61&67 are common ferrite materials. I've said enough.

As to LDMOS, if he doesn't understand tuning. How do you expect him to understand bias or bias set point or how to do active biasing/ ( bias only only when keyed and grounded when in standby). If anyone has done one and it doesn't have thermal tracking. Watch what it pulls current wise until device cools down while in standby. Not to mention want bias applied before actual Drive is supplied. So some kind of sequencer is needed. Or footpedal, no keying circuit.

Ok, this 11meter junkie on standby.

My Dogg!!!