I am wondering if turning down your wattage to about 1 watt or so for your amplifier is good for saving the life of your amp it runs cooler etc. Does this also lower your final output when running your amp? Lets say your amp runs 100 watts when being driven with four watts. What would you guesstimate runnig a watt and a half into your amp might get you. Also any other pro's and cons.
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Turning down dead key for amp?
- Thread starter hammer0630
- Start date
Will feeding your amplifier less power reduce it's output? Sure. Would making that amplifier do less amplifying, not 'work' as hard, mean that it could last longer? That's a pretty safe bet too, less heat build up being just one of the reasons for that. Is the ratio of the input power to the output power linear, a 1/4 of the input meaning a 1/4 of the output? No, it isn't. You can make a fairly close guess by thinking of it as being linear, directly proportional, but it just doesn't work that way for a number of reasons, circuit design being just one of them. Transistors and tubes are not 'linear' devices, their amplification isn't a 'straight' line on a graph, but a 'curve' that starts off sort of 'flat' and increases it's upward climb to a steeper angle as the amount of power fed to it increase. At some point it get's to the point of very little gain in power in relation to the amount of power being fed to it. Somewhere on that curve the rate of increase get's to be almost linear. Increase input and the output increases at a proportional rate. That portion of the device's amplification curve is the 'best' place to operate that particular device. The amplification is being done in the most efficient manner and is a good representation of the signal being fed to that device. There are other sections of that amplification curve that can produce a much larger output when compared to the input, but that is only 'good' when the 'quality' of the output doesn't matter, it isn't being distorted by being amplified. Works great for CW, but for voice modes it's just terrible. A "What did he say?", kind'a thing.
Each particular device has a different amplification 'curve', they all are NOT the same. Even two of the same devices are different a little bit, so things have to be adjusted for each particular device. Two transistors, or tubes, of the same model are going to be very slightly different. In most cases it probably won't even be noticeable, but there's a difference. So, if you 'assembly-line' an amplifier, sometimes you end up with a 'dud' unless you tune each amplifier separately according to the device(s) in that amplifier. Almost no one ever does that unless there are gross differences. It isn't ever as simple as it seems like it ought to be.
Another 'catch'!
Amplifiers can't tell that there are 'parts' to a signal, they only know that there's a total 'lump' of input that it is supposed to make 'larger'. Those 'parts' of a signal refer to the carrier and applied modulation for an AM signal. An amplifier can't 'adjust' that carrier/modulation, it can only amplify what's presented to it. It goes by -total- signal. The transmitter that does that feeding to the amplifier is supposed to handle that carrier to modulation, keep the ratio in the right proportion to produce a good signal. So, if you want to change that carrier/modulation ratio (change the percentage of modulation) the transmitter is where to do it. So what's the deal about tuning an amplifier with just a carrier/'dead key'? The reason is it's easier to do 'sort of right' than it is to do it right. Most people have no way of producing a steady, modulated signal to do testing/tuning with. That 'steady' type input can't be done by voice, whistling, it's just not steady enough. And then, if the amplifier is being operated in the 'linear' portion of it's amplification curve, just using a carrier will get you 'close'. [Does any of that sound familiar?
Is that a good technical explanation? Good grief no! But it get's the general idea across.]
- 'Doc
Each particular device has a different amplification 'curve', they all are NOT the same. Even two of the same devices are different a little bit, so things have to be adjusted for each particular device. Two transistors, or tubes, of the same model are going to be very slightly different. In most cases it probably won't even be noticeable, but there's a difference. So, if you 'assembly-line' an amplifier, sometimes you end up with a 'dud' unless you tune each amplifier separately according to the device(s) in that amplifier. Almost no one ever does that unless there are gross differences. It isn't ever as simple as it seems like it ought to be.
Another 'catch'!
Amplifiers can't tell that there are 'parts' to a signal, they only know that there's a total 'lump' of input that it is supposed to make 'larger'. Those 'parts' of a signal refer to the carrier and applied modulation for an AM signal. An amplifier can't 'adjust' that carrier/modulation, it can only amplify what's presented to it. It goes by -total- signal. The transmitter that does that feeding to the amplifier is supposed to handle that carrier to modulation, keep the ratio in the right proportion to produce a good signal. So, if you want to change that carrier/modulation ratio (change the percentage of modulation) the transmitter is where to do it. So what's the deal about tuning an amplifier with just a carrier/'dead key'? The reason is it's easier to do 'sort of right' than it is to do it right. Most people have no way of producing a steady, modulated signal to do testing/tuning with. That 'steady' type input can't be done by voice, whistling, it's just not steady enough. And then, if the amplifier is being operated in the 'linear' portion of it's amplification curve, just using a carrier will get you 'close'. [Does any of that sound familiar?
Is that a good technical explanation? Good grief no! But it get's the general idea across.]- 'Doc
The less complicated way to answer your question would be to look at the data sheet information for the output transistors or tubes in your amplifier.
Take to total output for that transistor and divide that by 4 and you'll have a close guestimation of what your amps carrier output should be,
So if your amps total PEP output is 400 watts then a 100 watt carrier is safe for the transistors and you can adjust your input power to achieve that carrier.
Take to total output for that transistor and divide that by 4 and you'll have a close guestimation of what your amps carrier output should be,
So if your amps total PEP output is 400 watts then a 100 watt carrier is safe for the transistors and you can adjust your input power to achieve that carrier.
If your amp is a hy drive it will need a 15-20 watt dead key...if it is not...it will need a 2-4 watt dead key....read your amps specs to be sure....so you do not fry it.
i dont think a 15-20 watt dead key, is a good idea on a 350HDV it has two 2879s id hit it with 5w MAX dk just my IMO
i dont think a 15-20 watt dead key, is a good idea on a 350HDV it has two 2879s id hit it with 5w MAX dk just my IMO
I was thinking of 8 pill hy-drive. :laugh:
RM ITALY-203
It is a RM-203 I am waiting delivery on. I have a 148gtl for a radio which is very easy to adjust the power output.
It is a RM-203 I am waiting delivery on. I have a 148gtl for a radio which is very easy to adjust the power output.
I would not put more than 2 watts of dead key into a RM-203. These amps will not last long with a 4 watt input.
I would go even a bit lower.....that is a small amp, 1 to 1.5 watts is about all you need and look for about 150 watts tops out of it........and stick a fan on it as well, not much heat sink there.
73
Jeff
73
Jeff
Those Amps don't last very long regardless!
"IF it were me"...I would go ahead and whack it with a 12w DK, just to see how long it takes before that 10ohm smoke appears...Maybe hit it with 18v's while at it!
....and let the sparks fly!
This way you'll have a good excuse to go buy a real Amp!
op:
I have a President Mckinely running into a Predator 225 amp. So I’m guessing about a 3 watt dead key from the radio. The only problem is that my Giant MFJ meter needs about 10 watts to calibrate for SWR. I talk on SSB mostly. I’m going to play around with the dead key on the radio while watching the meter with the amp on and see where the amp dead keys and swings the most from dead key. Is that a good idea in your opinion?
Since there are so many replies I’ll chime in and say that the dead key is only good on AM mode. I stated that I mainly talk SSB which doesn’t effect the power at dead key with no carrier on SSB.
Shadetree Mechanic
Delaware Base Station 808
Normally I will adjust the carrier with the amp on to be about 1/4 of the peak that it produces.
So I am going to attach a PDF if you open it and scroll down to the bottom left graph you will see a representation of Power Out compared to Power Input. This is for the now legendary Toshiba 2SC2879. It is rated as a 100w device by Toshiba notice it makes that power at say 4.5 watts input per device but it is totally saturated by 11w. The rate at which the curve flattens increases more and more as the power input climbs. If the company has rated it for 100w PEP and you run it at 140wPEP what do you think that does to the device? What would happen to your engine in your car or truck if you ran it at redline every time you used it? What happens if you run your car or truck at 1/3 redline on the hwy under moderate load? How often do they have to rebuild the engine on a Top Fuel Car??
Heat, moisture and vibration are the enemy of all electronics. An affordable watt/swr meter would be a good thing to have. It is a means to setup your radio and antenna system and a means to notice anything obvious like a drop in power or sudden increase of swr.
Each device is different. I just chose this one because I had it handy and I knew it had the graph I wanted. Sometimes an image is worth 1000 words.
Heat, moisture and vibration are the enemy of all electronics. An affordable watt/swr meter would be a good thing to have. It is a means to setup your radio and antenna system and a means to notice anything obvious like a drop in power or sudden increase of swr.
Each device is different. I just chose this one because I had it handy and I knew it had the graph I wanted. Sometimes an image is worth 1000 words.