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Tuning a 102"

The TnT 600HD has 4, 2 sc2879 Transistors in it, and if I remember right the Galaxy 95t2 is a high power radio running 2, 2sc2290 in the output section.

Yes it has a built in amp running a pair of 2sc2290's. X-Force, the makers of his amp recommends that as a driver. Even though it matches their recommended driver, it is still seriously over driving the 4 2sc2879's in the amp. The 2sc2879 transistor is rated at 100 watts output if memory serves. That would mean the advertised 600 plus watts that amp is running at can only be achieved by running those 2sc2879 transistors out of spec, and with that driver they are being run far out of manufacturers specifications.

This pushing bipolar transistors out of specification is commonly done today. hey will have a shorter use life because of this. It also means they generate a lot more heat then they normally would, which is also the enemy of bipolar transistors. I would love to see the problems these manufacturers would have trying to do the same with the newer RF mosfets...


The DB
 
Agreed.
I have a 400-12 Hi drive built by Carl at x-force, it is the same as the Magna force 600 or TnT 600HD, all 4 2979`s with a class b bias set-up
They pad the hell out of then input so it can soak up a lot of drive, but IMO 2 X 2290`s is still excessive.
A good dual final radio will drive 4 2879`s to full output.
The Guys that run hi voltage in mobile set-ups love this style amp because they drive the snot out of them at 17/18/19/20 volts and see huge numbers.......
If you keep the drive down, and run them at @14 volts they are fine.
Just do not expect a KW out of 4 2879`s.

73
Jeff
 
The 2879 is rated at either 125 or 150 watts PEP...can't remember which.

I would sooner think that, unless he has a power meter inline, he ran too much input to the amp and cooked it.
 
I would hazard a guess you ran too much radio into too small of amplifier...you drove a four transistor amplifier with a two transistor radio, and that's not healthy. A single 2879 can over saturate four 2879s, let alone two...

TNT600HD
Transistors 4 x 2SC2879

A Galaxy 95t2 does not have two 2879s it has two 2290s which is the manufacturer's recomended drive for that amp. The amp was purchased specifically to pair with this radio, because it is a high drive amp. Not all amps are Texas Stars with a max drive of 4W dk and 20W peak.

TNT600HD....*driver required-yes* *recomended driver - TNT 250(containing 2 2290 transistors)* 20W dk max or 300W dk from amp. Max input 240W

TNT900 same as 600HD with internal drivers... *2 2290s driving 4 2879s*

The amp was hit with less (though slightly but still less) DK than specified, and with much less swing than its max input. Is it safer to run this amp at a lower drive? Yes, absolutely. Did I overdrive it, not according to the people who make it.
 
100 pep from that transistor according to the spec sheet.

There is a very long thread in the Amp section about 2sc2879 transistors and what the absolute maximum amount of power is that they will produce.
Tom, W8JI a ham that has written a lot of stuff for the Ham radio community as well as being an engineer and designer of amplifiers for Ameritron took a single 2879 and mounted it in a test Jig on a copper plate, Tom's calculations showed it's possible to reach 300+ watts output deep in class C without exceeding the dissipation rating of the transistor.
That is balls to the wall and no one in there right mind would want to operate them like that for any period of time, not to mention that the signal would be far from clean at that number.
About 120/125 watts peak power is reasonable at 13.8 to 14 volts in a well designed amp if you want it to live well and run somewhat clean.


73
Jeff
 
The 2879 is rated at either 125 or 150 watts PEP...can't remember which.

I would sooner think that, unless he has a power meter inline, he ran too much input to the amp and cooked it.

100 pep from that transistor according to the spec sheet.

I have a Toshiba datasheet for the 2sc2879 open in front of me right now. Binrat is correct, 100 watt output. Here is a link if anyone wants to see for themselves. Input is listed at 6 watts typical, and 10 watts maximum per chip. So amp manufacturers are having people run astronomical amounts of power into these transistors. 40 watts should be the maximum drive assuming they don't have an attenuator of some sort built in the amp. Anyone think there is an attenuator in the amps sold by any of the big name amp sellers? Also looking at how hard they suggest driving these things... The one that X-Force recommends running to drive Roadrage's amp has an advertised and false output of 240 watts. 150 watts is a more realistic output, and is still almost 4 times the manufacturers of the bipolar transistors specifications for this amp.

Roadrage is correct when he said the amp is being pushed hard. It is obvious what caused the issue, and SWR was not it.

When used properly these transistors are used to 13 db (about 20 times) gain. The way they are advertised as being used they get maybe 6 db (about 4 times) gain. They are being pushed way beyond spec. They generate tons of excess heat. I would love to hook one up to a spectrum analyzer, I bet they are splattering all over the place...


The DB
 
A Galaxy 95t2 does not have two 2879s it has two 2290s which is the manufacturer's recomended drive for that amp. The amp was purchased specifically to pair with this radio, because it is a high drive amp

You are correct, and this is why they tell you that even a SWR of 1.5:1 is too high, because they know that at those drive levels the transistor`s are being pushed to the limits.
The harder you run the transistors, the more sensitive they are to reflected power.
They do say that the Amp will do ( driven) 1 KW peak when hit with that kind of drive, but that is asking a lot of the transistors, and they are on the edge.
I have seen 1 KW+ output from 4, 2sc2879`s when driven hard and the supply voltage was in excess of 20 volts..... briefly.
You do not want to do that with a daily driver set-up.
You will be better off to reduce the dead key and peak drive levels no matter what they claim just to make your amp last longer.
If not this is often the result.


73
Jeff
 

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As far as the coil is concerned you shouldn't need one on a 1/4 wave antenna such as the one you are running. If it is the proper length the capacitance and inductance should cancel each other. Adding an inductor of any kind will throw off this balance, as well as shorten the length that the antenna needs to be to be resonant. I am curious what an antenna analyzer would say about the resonant point of the antenna before and after this coil was added.

I only wish I had an analzyer.

Also note, an SWR match does not mean an antenna is resonant. While most antennas are designed to keep these two points close, it is possible for an antenna to be resonant at a wildly different impedance than 50 ohms. Tuning to resonance will net better performance than tuning to an SWR match.

That is what I was getting at. I had read that and it seemed like it made enough sense to be believable.



I believe you, you should recommend it quit smoking... horrid habbit... ;)

I do keep telling it to stop, but it just won't listen.

I see by previous posts on this and other forums that you did do research, at least on some things. That is more than many people do before running an amp. Amps can be expensive, and there is a lot of misinformation pertaining to them. They are also among the first places people go to increase their range when it should be their last. You at least did other stuff first.

I research research research. I tend to be a bit excessive compulsive. When I bought my wife her engagement ring. I researched diamonds, their grading, properties, color and clarity, angles and how they perain to brilliance. I also studied metalurgy of jewelry class metals, how its forged, properties of each metal, how they are alloyed and what they are alloyed with. By the time I bought it, I found that I knew more than 95% of the people working in jewelry stores. I ended up hand picking the diamonds individually, and had a ring custom built for $2000, then had a retail appraisal done on it and it appraised for 3 times what I had into it.

Unfortunately for me, there is much more to tranceiver radio systems than jewelry. I know enough to make myself dangerous. I will say that I think I have more information in the form of answers, than I have understanding of those answers. Which always leads to more questions and research. For me just having the answer isn't enough. In my opinion, knowledge isn't measured by the answers alone, but knowing the answer AND to understand how the answer was concluded. I mean, you can teach an ape to hold up two fingers every time someone says "what's 1+1", but that doesn't mean it can add.


The rating for the Wilson 5000 is based on the coil within it, not the coax used. Look it up, you will see that it is not rated for near that much power. It should be able to handle that amp though. I wouldn't trust the RG-58 myself either, unless I happened to know it was mil-spec. Even then I just don't like RG-58. LMR-400 would be overkill for the power rating of your amp I think. That being said, go for it.

That is just what I have at the moment. I figured it might not be the best available, it should at least be safe.
 
You are correct, and this is why they tell you that even a SWR of 1.5:1 is too high, because they know that at those drive levels the transistor`s are being pushed to the limits.
The harder you run the transistors, the more sensitive they are to reflected power.
They do say that the Amp will do ( driven) 1 KW peak when hit with that kind of drive, but that is asking a lot of the transistors, and they are on the edge.
I have seen 1 KW+ output from 4, 2sc2879`s when driven hard and the supply voltage was in excess of 20 volts..... briefly.
You do not want to do that with a daily driver set-up.
You will be better off to reduce the dead key and peak drive levels no matter what they claim just to make your amp last longer.
If not this is often the result.


73
Jeff

That would explain why the only thing that was actually hot to the touch was the power cable.

I have already decided to not only get my Rs down, I am goin to run my radio on it's lowest power setting. It should still yeild good numbers out of the amp but be much safer.

I could unbond my truck and have lower SWR, but I'm not going to. I think that having 550W put through a resonant antenna will have better results than a non-resonant antenna with low SWR and 800W through it.
 
I could unbond my truck and have lower SWR, but I'm not going to. I think that having 550W put through a resonant antenna will have better results than a non-resonant antenna with low SWR and 800W through it.

Unfortunately there is no easy way of knowing how close the antenna is to resonance without an antenna analyzer. To bad you don't live close to me or I would check it out for you for free...


The DB
 
100 pep from that transistor according to the spec sheet.


Isn't this rating at exactly 12.5 volts? A car is typically at least 13.8, if not 14.5 volts normally, which causes the output to be skewed. I want to remember there is one of the manufacturers that shows the voltage vs PEP output, and its closer to 125 per unit at a normal car charging system voltage.
 
A 1/4 wave whip the correct length will typically exhibit slightly low impedance in a mobile set-up, but almost every install is a bit different because body shapes of various cars/trucks, how well it is grounded and were the antenna is mounted influence this.
Most guys installing only have a SWR meter and that is fine, a long as the meter is telling you that SWR is about 1.5:1 the average radio will be happy.
When you get deeper into antennas and start using a antenna analyzer and looking at things more closely there is more to it than just SWR.
The Coil he is using helps to bring the match closer to 50 Ohms at the feed-point.


73
Jeff
 
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