hundreds of watts per 2879 ???????????????????????

[mackmobile43]

Here is an option for those on AM who want to experiment with getting about twice the output from 18 volts the easy way. First understand that you are risking your transistors if you make a mistake with drive or carrier level and your amplifier has to have a few key things in place. Many can do this without modification. You are also likely to splash more because of IMD.

The amplifier has to be class C. That means the bases of the transistors are at DC ground trough the input transformers. The amp should have 2SC2879 transistors. The capacitors across the output transformers and transistor collectors should be no higher then 680 pf. If your amp fits this description you can probably run 18 volts. Some 16 volt electrolitics may get warm.

You need a 6 volt battery. The bigger it is the longer you can talk. Place this battery in series with the positive 12 volt line feeding your amp. You can use a 6 volt battery charger powered from a cigarette lighter 110 volt AC inverter to charge the 6 volt battery. You could also just use the battery if you're not talking long and take it home to charge.

The most important thing to consider in order to prevent transistor failure is drive level. The amp will require LESS drive then it did on 12 volts. Your radio should have a variable RF power control on it. Drive should never be turned up past the point where the carrier exceeds 25% of the max PEP. If you use a true RMS meter this point is when the meter still moves the slightest bit forward with modulation. Not backwards.

Lower drive will increase reliability. One quick mistake with too much drive will burn open the transistor junctions! The amp will get hotter and may need more air flow. I don't offer this information here for anyone to try it. You need to know what you're doing and what the tradeoffs are. I offer the info for the guy that "needs" 18 volts the easy way but sees mounting alternators under the hood as not an option.

Are you saying to connect the 6 volt battery to the vehicles 12 volt system?

If so when this is done you make the vehicles entire electrical system into an 18 supplied system and I'm not sure if some if not most of the vehicles electrical components will stand the higher voltage over the stock 12to 14 volts it's designed to operate at.

 

[W5LZ]

There's always something, ain't there?
But then, if you're talking about competition, you are not talking about normal and reasonable expectations, or operating conditions/styles. What is common/typical/ or 'do-able' in one is never going to be common/typical/ or 'do-able' in the other.
'More' from 'Less' is certainly possible. But not very practical, and you will always 'pay' for it in some way.
- 'Doc

 

[Shockwave]

Are you saying to connect the 6 volt battery to the vehicles 12 volt system?

If so when this is done you make the vehicles entire electrical system into an 18 supplied system and I'm not sure if some if not most of the vehicles electrical components will stand the higher voltage over the stock 12to 14 volts it's designed to operate at.

No Mackmobile, You just put the 6 volt battery in series with the 12 volt wire that feeds your amp. The only thing that sees 18 volts then is the Amp. Everything else still runs on 12 volts.

 

[mackmobile43]

No Mackmobile, You just put the 6 volt battery in series with the 12 volt wire that feeds your amp. The only thing that sees 18 volts then is the Amp. Everything else still runs on 12 volts.

A battery with 2 paths to ground, hmmm.

 

[Shockwave]

A battery with 2 paths to ground, hmmm.

"Series" means only one path to ground for the 18 volts. Through the amplifier

 

[Shockwave]

I received several comments questioning how reliable an amplifier can be made to run when operating 2SC2879's at over 200 watts output each. Trust me, I've blown up enough of these transistors to determine exactly what their limitations are and developed a very effective way to prevent ever burning one out at close to these power levels.

When I messed around with these transistor amplifiers 20 years ago, I wanted to figure out an easy way to prevent transistor failure. The 2SC2879 blows up when you exceed 20 amps collector current by any significant amount. The goal is to limit the current and shut the entire amplifier down instantly if any transistor draws more then 20 amps.

When you have two transistors operating in a push / pull situation, only one transistor fires at a time so the bank of two should still only draw 20 amps max. I use a 20 amp blade fuse to feed voltage into the back center tap on each output transformer. The 20 amp fuse will limit the current so each transistor can make about 215 watts of output at about 18 volts. This headroom is needed because the fuse will not react fast enough if you protect at 250 watts.

Each output transformer will need it's own fuse. The DC feed on each transformer should be properly RF bypassed with a choke and .01 cap to ground before it connects to the fuse. To make a good RF choke wrap 3 turns of #12 wire around an RF core. The same core material you would use to make a small input combiner is perfect here.

That takes care of the current limit part, now for the instant shutdown when triggered. You will need one mini SPDT relay for each fuse. Use relays with 12 volt coils for 12 volts and 24 volt coils work good on 18 volts. The ground side of each relay coil should be tied together and switched to ground only when the amp is on. Otherwise the relays will draw current with the amp off. Each relay gets it's positive coil voltage from the load side of the individual fuses you added so it only gets power when the fuse is good. You should also place a reversed biased (stripe side to positive) 1N4001 diode across each relay coil to prevent inductive kickback.

Now wire all of the normally open contacts of the relays in series with each other. So that all of the relays have to be keyed to complete the connection. You next want to break the connection to the stock keying relay coil directly at the relay and place all of these normally open contacts in series with that. It is important to do this right at the RF keying relay and after any SSB delay capacitor. Otherwise the amp will not shut down quickly enough.

You treat an internal driver stage the same way except you can often use a smaller fuse like 10 or 15 amps to add further protection against overdrive. You can also add a thermal switch on the heatsink inline with the keying relay to open the circuit if the temperature gets too hot. Other variations include adding LED's and resistors to indicate what protection fuse opened up for quick replacement. That requires extra switching to prevent the load resistors from drawing current when the amp is off.

While this protection circuit may sound very simple, when I use to make them I charged quite a bit of money for the installation because I knew I would never see that amplifier again for repairs. You can even add reversal diodes at the load side of each fuse to protect against reverse polarity. This all makes for a virtually indestructible solid state amp especially when used only on AM.

Added info: This type of protection circuit may not be quick enough to protect the transistors in SSB use in every situation. Without the AM carrier to stabilize the average current drain, the fuse may not melt fast enough on some SSB audio peaks. This is for AM, FM, or CW only. SSB would require electronic protection triggered off voltage drops across shunts.

 

[dxhound]

Ashame I went camping....I could have responded to the ignorance faster.

If you still havent figured out how excessive current could affect a voltage barrier device, maybe you should go back to school.

As for the harmonics being produced by these types of amps when overdriven. The harmonic or artifact is so powerfull that the inteligence is actually being conveyed over the harmonic, and in alot of cases the 3rd harmonic is even more pronounced.

But I guess the engineers who wrote that into our technical orders for our electronic attack pods had no idea what they were talking about.

I will agree with you on one two things. The transistor will produce this power.But only for a few seconds......If that

And the fuses feeding the input transformers is a good idea.

Im done with this moronic post, So I will sit back and enjoy the threads that read. 1kw from my 4 pill smoked my amp....help me fix please

 

[Captain Kilowatt]

Ashame I went camping....I could have responded to the ignorance faster.

If you still havent figured out how excessive current could affect a voltage barrier device, maybe you should go back to school.

As for the harmonics being produced by these types of amps when overdriven. The harmonic or artifact is so powerfull that the inteligence is actually being conveyed over the harmonic, and in alot of cases the 3rd harmonic is even more pronounced.

But I guess the engineers who wrote that into our technical orders for our electronic attack pods had no idea what they were talking about.

I will agree with you on one two things. The transistor will produce this power.But only for a few seconds......If that

And the fuses feeding the input transformers is a good idea.

Im done with this moronic post, So I will sit back and enjoy the threads that read. 1kw from my 4 pill smoked my amp....help me fix please

Basically this thread is about trying to stuff ten pounds of shit into a five pound bag and has nothing to do with how much shit overflows the bag. Another example would be running 100 PSI in your car tires that are rated for 35 PSI. Sure it will do it but not for ever and you run the risk of killing someone when it blows but hey it will do it. :bdh:

 

[GLR]

Basically this thread is about trying to stuff ten pounds of shit into a five pound bag and has nothing to do with how much shit overflows the bag. Another example would be running 100 PSI in your car tires that are rated for 35 PSI. Sure it will do it but not for ever and you run the risk of killing someone when it blows but hey it will do it. :bdh:

But the latest fad is running Nitrogen in your tires at higher psi levels than recommended with your lesser class "air". What that has to do with recent comments here, well...more than it should.

 

[Shockwave]

Ashame I went camping....I could have responded to the ignorance faster.

If you still havent figured out how excessive current could affect a voltage barrier device, maybe you should go back to school.

As for the harmonics being produced by these types of amps when overdriven. The harmonic or artifact is so powerfull that the inteligence is actually being conveyed over the harmonic, and in alot of cases the 3rd harmonic is even more pronounced.

But I guess the engineers who wrote that into our technical orders for our electronic attack pods had no idea what they were talking about.

I will agree with you on one two things. The transistor will produce this power.But only for a few seconds......If that

And the fuses feeding the input transformers is a good idea.

Im done with this moronic post, So I will sit back and enjoy the threads that read. 1kw from my 4 pill smoked my amp....help me fix please

DX Hound, I graduated top in my class from Connecticut School of Electronics when it was one of the best rated electronics courses in the country. Just because you pretend to know what you're talking about when you use terms like "zener diode", "voltage barrier device", and "excessive current on the diode", doesn't tempt me to call you ignorant due to your lack of knowledge.

You use a zener diode for voltage regulation and a germanium diode is typically used to rectify high frequency RF to drive a DC meter movement. As for the harmonics that are produced and their ability to exaggerate the readings, you simply can't have it both ways my friend. It's not possible for an amplifier to produce 4 watts on the second harmonic and not show any increase in reflected power going into a resonant antenna load. Unless of course you have a dual band 11 and 6 meter antenna

Your theory about excessive current caused by harmonics on the diode in the meter is wrong too. Overdriving an amp does not put excessive current on the meters diode. The extra "fake" watts you see on a meter when you overdrive an amp to flat top has more to do with how the waveform looks to the meter then harmonics. The meter can't respond to instant changes in power levels. It merely looks at the average power and flat topping makes that average appear larger to the meter.

You really don't understand harmonics, IMD, or the power meters very well either but that's OK because I have the patience to explain it to you. It is in band IMD that causes the biggest problem with excessive drive. It increases exponentially with drive and can't be easily filtered out. Harmonics are completely different and can be filtered right out with a few coils and caps.

Your comment on only being able to make a couple hundred watts for a few seconds is silly. I can think of a dozen amps I did with date codes on the transistors from the early 1990's that still have them transistors in use today. You wouldn't be so frustrated with this post if you stopped trying to sell someone who knows what's going on that the facts are wrong.

PS. Name one case where 3rd order harmonics would be larger then second order?

 

[dxhound]

DX Hound, I graduated top in my class from Connecticut School of Electronics when it was one of the best rated electronics courses in the country. Just because you pretend to know what you're talking about when you use terms like "zener diode", "voltage barrier device", and "excessive current on the diode", doesn't tempt me to call you ignorant due to your lack of knowledge.

You use a zener diode for voltage regulation and a germanium diode is typically used to rectify high frequency RF to drive a DC meter movement. As for the harmonics that are produced and their ability to exaggerate the readings, you simply can't have it both ways my friend. It's not possible for an amplifier to produce 4 watts on the second harmonic and not show any increase in reflected power going into a resonant antenna load. Unless of course you have a dual band 11 and 6 meter antenna

Your theory about excessive current caused by harmonics on the diode in the meter is wrong too. Overdriving an amp does not put excessive current on the meters diode. The extra "fake" watts you see on a meter when you overdrive an amp to flat top has more to do with how the waveform looks to the meter then harmonics. The meter can't respond to instant changes in power levels. It merely looks at the average power and flat topping makes that average appear larger to the meter.

You really don't understand harmonics, IMD, or the power meters very well either but that's OK because I have the patience to explain it to you. It is in band IMD that causes the biggest problem with excessive drive. It increases exponentially with drive and can't be easily filtered out. Harmonics are completely different and can be filtered right out with a few coils and caps.

Your comment on only being able to make a couple hundred watts for a few seconds is silly. I can think of a dozen amps I did with date codes on the transistors from the early 1990's that still have them transistors in use today. You wouldn't be so frustrated with this post if you stopped trying to sell someone who knows what's going on that the facts are wrong.

PS. Name one case where 3rd order harmonics would be larger then second order?

I would say everyone agrees that Bird meters are of the best right? And chances are there engineers and designers are pretty smart in the RF field.... Maybe you should tell them they are as ignorant as I am ................Read page 9 http://www.repeater-builder.com/bird/pdf/bird-4360-4362.pdf

http://www.dxstore.com/download/Bird_43_Series_Manual.pdf
Pretty dumb huh??????

Yes you are correct that some harmonics within the freq. range of the meter will indicate an elevated SWR, but for the most part......Just higher power.

Also A zener diodes current will increase with reverse voltage.....reverse voltage being the returning harmonics. Zener Diodes Information on GlobalSpec

And yes you are correct that the clipped or flatop signals add to the problem of erroneous measurements, but a decent meters peak reading would remain the same.

Oh and this is more like 20 pounds of shit!!!!

And by pronounced, I meant the intelligence is actually cleaner and easier to understand not more powerful. But this might just be with what we deal with, with radar signatures

 

[BOOTY MONSTER]

WM1 Deluxe Computing SWR/WATTMETER. Autek Research

how would the WM1 compare to a bird for someone that will never need to measure more than 2000 watts ?

 

[dxhound]

Alot of people use them and like em... I prefer these for remote http://www.palstar.com/pm2000am.php

 

[pro151]

Alot of people use them and like em... I prefer these for remote Palstar.com: PM2000AM Watt Meter

Got 2 of them.
Good little meter!

 

[Shockwave]

I would say everyone agrees that Bird meters are of the best right? And chances are there engineers and designers are pretty smart in the RF field.... Maybe you should tell them they are as ignorant as I am ................Read page 9 http://www.repeater-builder.com/bird/pdf/bird-4360-4362.pdf

http://www.dxstore.com/download/Bird_43_Series_Manual.pdf
Pretty dumb huh??????

Yes you are correct that some harmonics within the freq. range of the meter will indicate an elevated SWR, but for the most part......Just higher power.

Also A zener diodes current will increase with reverse voltage.....reverse voltage being the returning harmonics. Zener Diodes Information on GlobalSpec

And yes you are correct that the clipped or flatop signals add to the problem of erroneous measurements, but a decent meters peak reading would remain the same.

Oh and this is more like 20 pounds of shit!!!!

And by pronounced, I meant the intelligence is actually cleaner and easier to understand not more powerful. But this might just be with what we deal with, with radar signatures

While Bird makes some of the best meters on the market, that Ham Mate is a piece of junk. The Bird 43 and many other quality meters can accurately measure power at 27 MHz and where the majority of harmonics end up at 54 MHz. Just use a 25 to 60 MHz slug.

Didn't you notice that those bright Bird engineers offered you the very same test on page 9 as I did here in my first posts with the low pass filter between the transmitter and the meter? Had you spent less time arguing and a little more time testing, you would see that adding the low pass filter will not shave off 50% of your output.

Are you still hung up on the mistake of a zener diode being used in any watt meter? I'm well aware of how a zener diode works because I've used them countless times before. The zener diode is just like an ordinary diode in the forward bias direction. It conducts current in the reverse direction when the reverse bias voltage hits the zeners turn on voltage. Not even remotely appropriate for rectification of RF.

The only real way to tell if flat topping may adding to your power reading is to look at it on the scope. Also if the harmonics drive the forward power reading up by 10% there is no way possible for it not to drive the reflected power up by at least as much. This is because a much larger percentage of the forward harmonic power will be reflected from the CB antenna.