I have a QJE 50 amp power supply with a voltage meter and a amperage meter powering a RM KL-503 which has 6 power settings at setting 1 the amp meter shows a forward swing using more amps as my Cobra 148GTL goes from 2 watts to 15 watts audio. At 3 power setting on the KL503 it hold steady at dk and with audio swing. Now at number 6 setting on KL 503 it shows on the amp gauge a dk of 28 amps and with audio it swings backwards at least 10 amps but what is confusing is I still get a wattage reading of nearly 100 watts forward with modulation? Why would my power supply meter show it using more amps on dk for every setting that is higher but on high audio makes it show it uses less amps but my inline wattage meter shows an increase with modulation?
-
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.
-
A Winner has been selected for the 2025 Radioddity Cyber Monday giveaway! Click Here to see who won!
50 amp supply swiging backwards on high
- Thread starter hammer0630
- Start date
sadly, you can trust the amp meter more than the wattmeter.
it is simply a case of your amplifier trying to draw more amps during modulation peaks than the power supply has on hand to deliver.
yes, the power supply says 50 amps continuous, and it may actually deliver that.
some dont. advertisers do get very creative with their product descriptions sometimes.
the 30 amp max draw of the amp is what is suspect to me.
getting 450 watts out of the amp and only drawing 30 amps makes me say hmmmm....
that seems like some advertising magic, as amplifier classes have inherent efficiency ratings, regardless of the transistors used.
ohms law is the law.
the only way to get more watts out with the same amp draw is to increase voltage.
if the voltage must stay the same, then more amps will be needed.
normally it would take a "4 pill" amplifier to get 450 watts out, and they draw up to 75-80 amps to make that happen.
i wish i had better news, but you probably just need a bigger power supply.
LC
it is simply a case of your amplifier trying to draw more amps during modulation peaks than the power supply has on hand to deliver.
yes, the power supply says 50 amps continuous, and it may actually deliver that.
some dont. advertisers do get very creative with their product descriptions sometimes.
the 30 amp max draw of the amp is what is suspect to me.
getting 450 watts out of the amp and only drawing 30 amps makes me say hmmmm....
that seems like some advertising magic, as amplifier classes have inherent efficiency ratings, regardless of the transistors used.
ohms law is the law.
the only way to get more watts out with the same amp draw is to increase voltage.
if the voltage must stay the same, then more amps will be needed.
normally it would take a "4 pill" amplifier to get 450 watts out, and they draw up to 75-80 amps to make that happen.
i wish i had better news, but you probably just need a bigger power supply.
LC
All power supplies have two ratings, the amount of current that can be supplied continuously (CCS) and the amount of current that can be supplied for very short periods of time (ICS). The ICS is always larger than the CCS and is the one advertised because it makes that power supply seem 'larger', more 'capable'. The differences between those two ratings isn't 'set', it varies because of how the supply is made. A very 'stiff' power supply might have a CCS of maybe 75% of the ICS rating. The average power supply has a difference of maybe 60%.
One very rough way of figuring how much current is required for an amplifier (solid state ones) is to divide the max power output by the supplied DC voltage, multiply that by 2 and that's the required current for that power output. Why that '2'? Because all solid state amplifiers are only about 50% efficient. At least half the current supplied to that amplifier is used to produce it's output. You can't get something for 'nuthing.
That's a very 'rough' guess, but it's certainly closer than most advertising.
Your watt meter isn't 'wrong', it's reading what's coming out of the amplifier correctly. The thing is that you have to understand what's happening in that amplifier (AM mode!). If the thing is 'swinging' backwards it typically means it's over-modulated. That means that at particular times zero power is being produced because there's too much modulation power being applied to a carrier, which results in a zero output. You can't have a 'negative' power, there ain't no such thingy. That means that at those points the amplifier is 'sucking', not 'blowing'. (Howz that for an analogy??
)
- 'Doc
One very rough way of figuring how much current is required for an amplifier (solid state ones) is to divide the max power output by the supplied DC voltage, multiply that by 2 and that's the required current for that power output. Why that '2'? Because all solid state amplifiers are only about 50% efficient. At least half the current supplied to that amplifier is used to produce it's output. You can't get something for 'nuthing.
That's a very 'rough' guess, but it's certainly closer than most advertising.
Your watt meter isn't 'wrong', it's reading what's coming out of the amplifier correctly. The thing is that you have to understand what's happening in that amplifier (AM mode!). If the thing is 'swinging' backwards it typically means it's over-modulated. That means that at particular times zero power is being produced because there's too much modulation power being applied to a carrier, which results in a zero output. You can't have a 'negative' power, there ain't no such thingy. That means that at those points the amplifier is 'sucking', not 'blowing'. (Howz that for an analogy??
)- 'Doc
Something is being overlooked here. Hammer never said the volt meter on this power supply was dropping under load and that would be the first indication the power supply is too small. On the other hand, when an amp meter drops under modulation it's much more likely you are overdriving the amp with carrier.
It is never mentioned what the carrier level is during these conditions however we know the carrier is at 28 amps and drops to 18 under modulation. That's 386 watts of input power for the carrier. The RM amp is biased so even at 50% efficiency we are talking about 193 watts of output.
That is almost double what this amp could make and still modulate the positive peaks to 4 times the carrier level. You'll probably get your best results with the amp on high power and with the carrier at the radio reduced to make the amp key 100 watts.
It is never mentioned what the carrier level is during these conditions however we know the carrier is at 28 amps and drops to 18 under modulation. That's 386 watts of input power for the carrier. The RM amp is biased so even at 50% efficiency we are talking about 193 watts of output.
That is almost double what this amp could make and still modulate the positive peaks to 4 times the carrier level. You'll probably get your best results with the amp on high power and with the carrier at the radio reduced to make the amp key 100 watts.
50 amps is also the most current four of the largest 12 volt bipolar transistor should ever draw total. The 2SC2879 still reigns king in this area at a maximum collector current of 25 amps. Four of these transistors in the classic push-pull configuration will NEVER draw close to 100 amps.
That's because in the four transistor amplifier, only two transistors will be drawing current at any given time. That is how push-pull works. In a bank of two transistors, one transistor will fire into the output transformer to make half of the sinewave. It will switch off at the crossover point where the other transistor will fire and complete the other 180 degrees.
Note: This information relates to the RF signal and not DC bias. Bias will cause all of the transistors to draw a low level idling current. Bias was not considered here since it will only consume a very small percentage of the overall operating current.
That's because in the four transistor amplifier, only two transistors will be drawing current at any given time. That is how push-pull works. In a bank of two transistors, one transistor will fire into the output transformer to make half of the sinewave. It will switch off at the crossover point where the other transistor will fire and complete the other 180 degrees.
Note: This information relates to the RF signal and not DC bias. Bias will cause all of the transistors to draw a low level idling current. Bias was not considered here since it will only consume a very small percentage of the overall operating current.
The answer is easy. Your amp meter in the DC line has a much easier time measuring average current with modulation than the typical watt meter does at measuring average power.
Watt meters have to rectify and filter the RF to some degree in order to drive a DC meter movement. Most watt meters will have a capacitor in them to filter the rectified RF that attempts to charge to the peak voltage level.
This is true with most inexpensive "average" watt meters and causes them to exaggerate average modulated power readings. This is why a true average meter like the Bird 43 will typically show much less modulated power than other meters.
The Bird 43 will also behave the same way a DC current meter feeding the final stage would. If the amp meter goes down with modulation, so will the Bird. If the Bird goes forward with modulation, so will the amp meter.
My voltage meter never fluctuates and is adjustable and has no problem raising the voltage level past 13.8 under the heaviest load I can put on it. I tried using ssb and making a constant level of sound and it does reach and maintain 32 amps indefinitely which is approximately 4 more amps than my am dk. And again my am dk is 2 watts but does nearly 15 watts modulation and ssb peaks at 18 watts. Now besides my 2 watt am carrier it peaks at 15 watts and ssb at 18 watts and that seems to equate that 3 more watts would consume 4 more amps? But then where does 10 amps decrease come into play when 15 watts is applied? And yes I can hardly understand what I just wrote!
just out of curiosity,
can you put an SWR meter between the radio and the amp, and post the SWR going into the amp at each power level?
then put the SWR meter between the amp and the antenna and do the same thing. post the SWR at each power level on the amp.
LC
can you put an SWR meter between the radio and the amp, and post the SWR going into the amp at each power level?
then put the SWR meter between the amp and the antenna and do the same thing. post the SWR at each power level on the amp.
LC
Agreed, 15 watts dead key is way too much, like posted above set the dead key at no more than 2 to 2.5 watts and try it there. You are going to kill that thing. I run a magna force 350HD and I use a dead key setting of 2.5 watts swinging to around 60-70. Works good, and the amp never gets warm.