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which davemade

The problem with manufacturers using the IFR520 FET is that that device was never intended for RF. It is a high speed switching FET that just happens to work at 27 MHz. If REAL honest to goodness RF FET's were used in radios and amps then the results would be vastly different. Commercial gear has used Fet's for decades with great success. I have a 6m amp that uses four MRF151G's for 1200 watts output.n It is REALLY clean. It has to be. It was originally a Larcan television amplifier but it does require 50 volts. There are plenty of 12 volt RF FET devices out there that will run circles around the IFR520 in both power output and quality of signal.
 
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But the thing is, is that those true RF FETs are pricey and its cheaper to through a few switching FETs into an amp instead of the real deal.
Captain, you got me thinking of a winter project now.... damn you. :D
 
Captain Kilowatt said:
The problem with manufacturers using the IFR520 FET is that that device was never intended for RF. It is a high speed switching FET that just happens to work at 27 MHz. If REAL honest to goodness RF FET's were used in radios and amps then the results would be vastly different. Commercial gear has used Fet's for decades with great success. I have a 6m amp that uses four MRF151G's for 1200 watts output.n It is REALLY clean. It has to be. It was originally a Larcan television amplifier but it does require 50 volts. There are plenty of 12 volt RF FET devices out there that will run circles around the IFR520 in both power output and quality of signal.
Click to expand...

Agreed. There are some RF fets out there that will do a very nice job but not many will pay the price. A local has been gathering parts to build a fairly large amp with a few of the LDMOS transistors. I think a big tube or two would be cheaper in the end but he's more interested doing something different. I believe one of the reasons that you rarely see high quality CB equipment is because there is no demand for it. People want big watt meter readings, top notch workmanship, stellar customer service and they want it dirt cheap.
 
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Texas Star amps are overrated and overhyped!!! The only reason people buy them is because the only other choices are Palomar, Palomar clones, or KLV.
It's a choice between stepping in cow crap, bear crap, or dog crap.
Too bad Messenger is no longer in business, they made some nice amps.
I sure do miss my Messenger M500 which had NO tuning issues whatsoever.
 
All DaveMade 12 volt solid state amps are going to be class C unless you pay to have them biased ( Call Joe at DaveMade And ask him about IMD and bias)
At 13 stock volts the texas star 500 will beat the average 2 pill class c "comp" amp like cornbread batter.
Simple math tells you that 4 2879`s will produce more power than 2 2879`s
Any biased amp will show higher gain than class c.
If you run the older T/S amps within the limits set by the guys building them they are fine.
I have one that is at least a decade old and has had nothing replaced in it, in fact I was using it on ten meters just this morning.
Stay away from the 667, it is a very cranky amp, and now that they are using MOSFETS in the drive section I have no idea how reliable they are.
I will agree that as of late T/S is not what it used to be in terms of how they stand behind the product they make.

The advantage goes to the "comp" boxes when you start volting the Amp.

You really do not want to go buy a Dave(Joe) Made amp, tear it apart and rebuild it with bias.....
Davemade got its claim to fame when they found out that toshiba 2879`s could be pushed way beyond the numbers posted in the spec sheets.
No other 12 volt transistor could be abused like this transistor and still live to key a second time, voltage as high as 20 volts, stupid amounts of drive and power dissipation that reached as high as 250 watts.
Dave boxes were a design that was inspired by high frequency power supply`s for Plasma Cutters.
Also contrary to popular myth, the use of the large toroids on the output transformers like all the comp style builders use today was first used by Abe Brewer many years ago in the Varmint SS600.
If I were going to buy a "cb" style amp today it would be X force, the TNT line, at least they attempt to use some kind of bias.
Forget about any 1 pill design, it is not even push pull.
I also wish Ray Messenger was still around building amps, yes they were biased a little hot, but the were a good amp.
Where is 1-800 Toll Free when you need him?

73
Jeff
 
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AudioShockwav said:
All DaveMade 12 volt solid state amps are going to be class C unless you pay to have them biased ( Call Joe at DaveMade And ask him about IMD and bias)
At 13 stock volts the texas star 500 will beat the average 2 pill class c "comp" amp like cornbread batter.
Simple math tells you that 4 2879`s will produce more power than 2 2879`s
Any biased amp will show higher gain than class c.
If you run the older T/S amps within the limits set by the guys building them they are fine.
I have one that is at least a decade old and has had nothing replaced in it, in fact I was using it on ten meters just this morning.
Stay away from the 667, it is a very cranky amp, and now that they are using MOSFETS in the drive section I have no idea how reliable they are.
I will agree that as of late T/S is not what it used to be in terms of how they stand behind the product they make.

The advantage goes to the "comp" boxes when you start volting the Amp.

You really do not want to go buy a Dave(Joe) Made amp, tear it apart and rebuild it with bias.....
Davemade got its claim to fame when they found out that toshiba 2879`s could be pushed way beyond the numbers posted in the spec sheets.
No other 12 volt transistor could be abused like this transistor and still live to key a second time, voltage as high as 20 volts, stupid amounts of drive and power dissipation that reached as high a 250 watts.
Dave boxes were a design that was inspired by high frequency power supply`s for Plasma Cutters.
Also contrary to popular myth, the use of the large toroids on the output transformers like all the comp style builders use today was first used by Abe Brewer many years ago in the Varmint SS600.
If I were going to buy a "cb" style amp today it would be X force, the TNT line, at least they attempt to use some kind of bias.
Forget about any 1 pill design, it is not even push pull.
I also wish Ray Messenger was still around building amps, yes they were biased a little hot, but the were a good amp.
Where is 1-800 Toll Free when you need him?

73
Jeff
Click to expand...

Your math is correct. I suppose I didn't spell it out clearly enough. I would rather have a smaller amp of better quality than a larger Texas Star.

Someone that already has a comp style box and doesn't want class C can add bias without ripping it apart. If they aren't capable of taking something they already have or can get for cheap and adding a simple circuit to it they certainly don't need to buy an old Texas Star or any old equipment that's been passed around the CB shops. Nothing was said about buying a new amp and modifying it.

Do you mean a plasma cutter as in metal fabrication or plasma generator used in the medical field? :confused:
 
543_Dallas said:
Agreed. There are some RF fets out there that will do a very nice job but not many will pay the price. A local has been gathering parts to build a fairly large amp with a few of the LDMOS transistors. I think a big tube or two would be cheaper in the end but he's more interested doing something different. I believe one of the reasons that you rarely see high quality CB equipment is because there is no demand for it. People want big watt meter readings, top notch workmanship, stellar customer service and they want it dirt cheap.
Click to expand...


I believe there is no demand for high quality CB amps because a great deal of people do not know any better and do not care to know any better as long as they THINK they are getting the numbers out of the box that they think they are. That has been shown time and time again right here on this forum when the subject of class C versus class ab comes up when someone starts talking about the pros and cons. A LOT of people just plain do not give a shit about anyone else other than themselves. Listen to ch 6 sometimes for proof. Manufacturers know this and continue to make amps with shitty switching FETs because they know people will continue to buy them as long as they think they are getting the numbers out the meter is showing. Since these amps are illegal in the first place what is someone going to do about it when they realize they have inferior components installed in them?
 
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binrat said:
But the thing is, is that those true RF FETs are pricey and its cheaper to through a few switching FETs into an amp instead of the real deal.
Captain, you got me thinking of a winter project now.... damn you. :D
Click to expand...


So how many IRF520's are you going to order? :p

I have a couple projects to get done this winter. One is COMPLETELY rearranging the shack operating desk which I have started and hope to finish in the next few days. It seems every time I try a layout I forget something and then need to change things around again. After that is done I have a BIG amp project to get started on but it does not use any solid state components but rather a tube instead. A single 3CX3000A7 should be nice and clean and have no problems running at OUR Canadian legal limit as long as I can drive it hard enough. I may have to look at getting one of those HF rigs with 200 watt finals. :D
 
Some HF power supplies for many plasma applications run at 27.12 MHz, including some of the plasma cutters used in metal fabrication, plasma chemical vapor deposition, and similar plasma-assisted processes such as plasma etching, CO2 lasers and other process applications.
Many are designed to work into 50 Ohm loads.
There are other frequencies used as well 1, 2, 4, 13.56, 27.21, 40.86, 60, 80 and 100 MHz.
Some of the applications of switch mode devices used for RF can be gleaned from these applications as well, I don`t think some CB er dreamed up using switch mode devices for RF. ( IMHO)
As the supply of bi-polar transistors started to dry up, lots of people scrambled for a cheap alterntive, they found that these were being used for RF in industral applications and tried them for CB Finals, and then amps.
There are RF power supply's that run at 27 MHz that produce @500 watts from a single plastic TO 247 MOSFET device that was really designed to work in a switch mode application.
There is more going on at 27 Mhz than just CB amps.

Also, (IMHO) the company making 2879`s today will never achive the rugged build of the Toshiba, and the days of Keydowns using solid state devices run at 18/19/20+ volts is going to go away.
There are very nice MOSFET devices now that make awesome power and are all but bullet proof to SWR problems, it just that they do not run on or around 12 volts.

But, what do I know, I am a old dog.


73
Jeff
 
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C class amps are spec'd for FM; not AM.
B Class amps are better suited for AM use.
AB class amps are spec'd for both AM and SSB.
Not theory.

If Davemade put in a real regulated bias circuit, told their customers to run their amps @ 12.5v, recommended limiting the input power into their amps to the transistor specs, as well as recommended using a clean radio into the amp as they should, they would have few - if any - customers.

But then again - I can't stand 'death metal' music . . .
 
binrat said:
A single MRF151G amp for 80/40/20/10.
I have one of those 200 watt rigs. Its going so I can go real big....KX-3. The maybe a homebrew amp for the truck for it.
Click to expand...


Sounds like fun but why no 15m? With a single MRF151G it is simple to make it broadband. The Larcan 6m amp I have has four MRF151G's in it and it makes an easy kilowatt without breaking a sweat. It is speced at 1200 watts continuous 24/7/365 in the television VHF-Lo band. I also have four more sitting in a 1.2 kilowatt FM broadcast band amplifier module which consists of four boards and combiner/splitters which will have to be scrapped and just the FET's salvaged. Sometime down the road I may build an amp with one or maybe two of them for 2m SSB.
 
AudioShockwav said:
Some HF power supplies for many plasma applications run at 27.12 MHz, including some of the plasma cutters used in metal fabrication, plasma chemical vapor deposition, and similar plasma-assisted processes such as plasma etching, CO2 lasers and other process applications.
Many are designed to work into 50 Ohm loads.
There are other frequencies used as well 1, 2, 4, 13.56, 27.21, 40.86, 60, 80 and 100 MHz.
Some of the applications of switch mode devices used for RF can be gleaned from these applications as well, I don`t think some CB er dreamed up using switch mode devices for RF. ( IMHO)
As the supply of bi-polar transistors started to dry up, lots of people scrambled for a cheap alterntive, they found that these were being used for RF in industral applications and tried them for CB Finals, and then amps.
There are RF power supply's that run at 27 MHz that produce @500 watts from a single plastic TO 247 MOSFET device that was really designed to work in a switch mode application.
There is more going on at 27 Mhz than just CB amps.

Also, (IMHO) the company making 2879`s today will never achive the rugged build of the Toshiba, and the days of Keydowns using solid state devices run at 18/19/20+ volts is going to go away.
There are very nice MOSFET devices now that make awesome power and are all but bullet proof to SWR problems, it just that they do not run on or around 12 volts.

But, what do I know, I am a old dog.


73
Jeff
Click to expand...

Is spectral purity much of a concern with any of the plasma related devices that use these switch fets you mentioned?
AudioShockwav said:
Some HF power supplies for many plasma applications run at 27.12 MHz, including some of the plasma cutters used in metal fabrication, plasma chemical vapor deposition, and similar plasma-assisted processes such as plasma etching, CO2 lasers and other process applications.
Many are designed to work into 50 Ohm loads.
There are other frequencies used as well 1, 2, 4, 13.56, 27.21, 40.86, 60, 80 and 100 MHz.
Some of the applications of switch mode devices used for RF can be gleaned from these applications as well, I don`t think some CB er dreamed up using switch mode devices for RF. ( IMHO)
As the supply of bi-polar transistors started to dry up, lots of people scrambled for a cheap alterntive, they found that these were being used for RF in industral applications and tried them for CB Finals, and then amps.
There are RF power supply's that run at 27 MHz that produce @500 watts from a single plastic TO 247 MOSFET device that was really designed to work in a switch mode application.
There is more going on at 27 Mhz than just CB amps.

Also, (IMHO) the company making 2879`s today will never achive the rugged build of the Toshiba, and the days of Keydowns using solid state devices run at 18/19/20+ volts is going to go away.
There are very nice MOSFET devices now that make awesome power and are all but bullet proof to SWR problems, it just that they do not run on or around 12 volts.

But, what do I know, I am a old dog.


73
Jeff
Click to expand...

How important is spectral purity when it comes to these plasma devices? The switching fets being used for RF just seems like using a flat head screwdriver as a pry bar.
 

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