Input amps for my Linear amp?

[Snitch321]

Hi Guys,
I have purchased a RM KL800 linear amp, which shows a 600watt output and requires 30 amps, 24v input. Now i have purchased a power supply that matches, which provides 30 amps, 24v out. However, my question is because the plug socket in the linear power supply is 13 amps, then i take it, it is not getting the required amperage neccessary to fully power the linear amp? And i would need to replace the fuse with a 30amp one?

 

[Lauri-CoyoteFrostbite]

If the line into your power supply is rated at 13 Amps for what assume is 120 VAC, then the standard household current should handle it fine. A good vacuum cleaner can pull close to that. It sounds like this 24 volt power supply is properly fused for 30 Amp output---

The fuses in either line will not introduce resistance sufficient in any way to effect the operation of your new amplifier..... do not replace any fuses for a higher rating !



Lauri

 

[prcguy]

Do what she says....

24V at 30A from your power supply is 720 watts of power. 120 volts at 13 amps on the input side of your power supply is 1,560 watts and if its a linear power supply its probably around 50-60% efficient, so that 1,560 watts of input power is required to produce 24 volts at 30 amps DC (720 watts) to feed your amplifier. The missing power is lost as heat in the process.

An RF power amplifier is not 100% efficient and varies with type, maybe 70% or so for a common class C type made for CB service. I would expect a class C amp to draw about 857 watts of input power to put out 600 watts of RF power. Since your power supply is rated 24 volts at 30 amps (720 watts) that would power a 70% efficient class C amplifier to about 500 watts output before exceeding the power supply specs. That is about all you can expect. If your amplifier is a less efficient class like AB1 it will put out even less power with the 30A power supply you have.

I see the specs on your amplifier is 500-600 watts maximum output with a supply voltage of 20-30V DC. I would think to get 600 watts out of that amp you would need to feed it more like 28-30 volts and then at 30 amps of current it might do 600 watts. Maybe.

 

[merlin]

I had to ferret out the specs for this amp, and looks to me like 30 amp fuses would be adequate.
13 to 15 amp line fuse.
Note here that these Chinese THINGS are grossly overrated.
A claim of 600 watt PEP output is about burnout level and that is with 30 amp fuses.
You might squeeze 300 watt PEP out of this and that is being way overdriven.
Compared to other amps on the market, this one does have a level of protection and a low pass filter.
Keep the drive down and with a 2 tone generator and analyzer, you can check the linearity mandated by SSB.
The joke here is 1 Kw PEP max. You get that out of this, the devices already popped and too much smoke got out.

 

[AK9R]

Note here that these Chinese THINGS are grossly overrated.

What "Chinese thing" are you talking about? RM amps are made in Italy, I believe.

 

[merlin]

OK, thanks for the input.
Maybe you know if this is class C or AB ?

 

[Snitch321]

If the line into your power supply is rated at 13 Amps for what assume is 120 VAC, then the standard household current should handle it fine. A good vacuum cleaner can pull close to that. It sounds like this 24 volt power supply is properly fused for 30 Amp output---

The fuses in either line will not introduce resistance sufficient in any way to effect the operation of your new amplifier..... do not replace any fuses for a higher rating !



Lauri

Thanks Lauri, i appreciate you cobfirming it is working as should. Just so i can understand it, so essentially the linear amp powerful supply will pull to the limit of the 13amps? And that is sufficient to supply the right level of wattage eventually to the linear amp (600 odds wattage)

If the line into your power supply is rated at 13 Amps for what assume is 120 VAC, then the standard household current should handle it fine. A good vacuum cleaner can pull close to that. It sounds like this 24 volt power supply is properly fused for 30 Amp output---

The fuses in either line will not introduce resistance sufficient in any way to effect the operation of your new amplifier..... do not replace any fuses for a higher rating !



Lauri

Thanks Lauri, i appreciate you cobfirming it is working as should. Just so i can understand it, so essentially the linear amp powerful supply will pull to the limit of the 13amps? And that is sufficient to supply the right level of wattage eventually to the linear amp (600 odds wattage

Do what she says....

24V at 30A from your power supply is 720 watts of power. 120 volts at 13 amps on the input side of your power supply is 1,560 watts and if its a linear power supply its probably around 50-60% efficient, so that 1,560 watts of input power is required to produce 24 volts at 30 amps DC (720 watts) to feed your amplifier. The missing power is lost as heat in the process.

An RF power amplifier is not 100% efficient and varies with type, maybe 70% or so for a common class C type made for CB service. I would expect a class C amp to draw about 857 watts of input power to put out 600 watts of RF power. Since your power supply is rated 24 volts at 30 amps (720 watts) that would power a 70% efficient class C amplifier to about 500 watts output before exceeding the power supply specs. That is about all you can expect. If your amplifier is a less efficient class like AB1 it will put out even less power with the 30A power supply you have.

I see the specs on your amplifier is 500-600 watts maximum output with a supply voltage of 20-30V DC. I would think to get 600 watts out of that amp you would need to feed it more like 28-30 volts and then at 30 amps of current it might do 600 watts. Maybe.

Thanks for confirming. I replied yo Lsurie but by what it sounds, the 13 amp draw is enough to get the wattage output required all down the line to my linear amp near 600 watts?

Sorry i should of included the linear power supply model: PTS 230, which states input 230v

 

[K7MEM]

Maybe you know if this is class C or AB ?

Yes. The specs for the RM KL800 "linear" amp states "All Mode" (AM/FM/CW and SSB). So it must be all the above.

 

[Lauri-CoyoteFrostbite]

Hi 321

I would not worry about your power supply being unable to handle the amplifier. Unless it is plugged into an old house's wiring or something unusual, the line current will remain stiff and not vary more than a few percentages even at maximum load. You should expect a clean 20 Amp's from any modern household source.

One thing I will suggest is you not run your amplifier full-out on a continuous mode like FM or RTTY-- not that it can't handle it, its just that things are going to get hot and you risk a thermal run-away if the internal protection circuits fail. And they do fail ! (voice of experience.)

On the other hand, I am imagining you will be using this amp for SSB. The current demand will only come on voice peaks and everything, even at maximum, should remain cool and copacetic.

Sort of an aside-- years ago I was talking to a station manager of a high power'd HF SSB fixed station. He told me that when they first went on the air the electric company was unable to correctly bill them for their power usage. The transmitters were these super blow torch's, yet the electric bills hardly reflected any usage at all.
It seems that the conventional meters the power company installed were of a mechanical design. The clock-like mechanisms were unable to quickly respond fast enuff to the SSB peaks to register these current draws.

Your 600 Watt amp will run very similar to this on SSB. It will deliver current just fine with recovery between voice peaks charging the filter capacitors keeping the output stiff. I would not expect this to be reflect'd much in your electric bill, however .

Now, stop worrying about this an go enjoy your new 'blow torch.'

Lauri



.

 

[merlin]

Yes. The specs for the RM KL800 "linear" amp states "All Mode" (AM/FM/CW and SSB). So it must be all the above.

Hmm the specs say nothing of the class. AM, FM, CW, FSK, all work fine with class C, but not SSB.
To save production cost, all these bargain basement amps do not have any form of biasing on the devices. They add a capacitor to the switching relay to prevent SSB chatter and call it SSB compatible.. you look at the spectrum and it is awful. it will sound awful on SSB.
A good look at the insides, I could tell you for certain.
To get 600 watts, means at least 2 stages, the first stage usually biased to class A, that drives the second stage biased for class AB.
A fast way to check is with no input, measure the idle B+ current. A true linear will have about 160 Ma bias. If it is zero, so is the bias making it class C.

 

[RFI-EMI-GUY]

Seeing as you intend to use that as a base station. You might want to put a harmonic filter after that thing and keep the drive down low so you don't splatter 6 channels and have harmonics in the aviation bands. Those will get you a lot of attention from the friendly candy company.

 

[Snitch321]

Hi 321

I would not worry about your power supply being unable to handle the amplifier. Unless it is plugged into an old house's wiring or something unusual, the line current will remain stiff and not vary more than a few percentages even at maximum load. You should expect a clean 20 Amp's from any modern household source.

One thing I will suggest is you not run your amplifier full-out on a continuous mode like FM or RTTY-- not that it can't handle it, its just that things are going to get hot and you risk a thermal run-away if the internal protection circuits fail. And they do fail ! (voice of experience.)

On the other hand, I am imagining you will be using this amp for SSB. The current demand will only come on voice peaks and everything, even at maximum, should remain cool and copacetic.

Sort of an aside-- years ago I was talking to a station manager of a high power'd HF SSB fixed station. He told me that when they first went on the air the electric company was unable to correctly bill them for their power usage. The transmitters were these super blow torch's, yet the electric bills hardly reflected any usage at all.
It seems that the conventional meters the power company installed were of a mechanical design. The clock-like mechanisms were unable to quickly respond fast enuff to the SSB peaks to register these current draws.

Your 600 Watt amp will run very similar to this on SSB. It will deliver current just fine with recovery between voice peaks charging the filter capacitors keeping the output stiff. I would not expect this to be reflect'd much in your electric bill, however .

Now, stop worrying about this an go enjoy your new 'blow torch.'

Lauri

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Omg you are so informative and wise, i appreciate the time you took to explain things!

 

[K7MEM]

Hmm the specs say nothing of the class. AM, FM, CW, FSK, all work fine with class C, but not SSB.

What can I say. You must be reading something different than what I am reading.

To get 600 watts, means at least 2 stages, the first stage usually biased to class A, that drives the second stage biased for class AB.

The user manual and the schematic are available on-line. Check it out. The amplifier consists of two parallel push-pull stages. While it might benefit from two stages, there is no initial class A stage. And, while it is listed as "wide band" it is really only designed for 24-30 MHz. There is bias applied to support SSB.

The design of these power amps dates back to the 70's and 80's, when Motorola came out with a series of application notes on wide band amplifiers (3-30 MHz). They were published in the Motorola RF Device data book. I still have a copy on the shelf. The amp vendors just copied their designs and they haven't changed since. For example AN-593. There are other app notes that discuss designs all the way up to 1KW using only parallel push-pull stages. They are designed for SSB service, but will handle other modes as well. The app note is for a relatively low powered amp, but they just use bigger transistors and more of them to get to 600 watts.

Years ago, there was a ham that had a similar amp (1KW) configured in a backpack, and walked around the Dayton Ham fest. He was operating pedestrian mobile most of the time. They had it tested and it really was 1KW. I'm not sure how smart that was because, the antenna was about 3 inches from his head.

I have a small amp that I bought at a ham fest over 20 years ago for about $20. It is called a Pride-150 (5W input, 150W Output). I wanted something for 10 Meters to boost my HTX-100, and I was curious about the design. I was very surprised when I opened it up and saw that the design was right out of the pages of the Motorola manual. The bias is a little crude, but it works. The Motorola designs usually had better bias schemes.