We need a linear power amp for lab work that will operate in the 2 to
4MHz range and deliver 50W continuous at 300+ volts.Input signal would be via a function generator.
Is there anything like this, or close to this, available off-the-shelf?
Thank you,
Jim Clark
Check out AR:
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
How about some HF power amp and a step up transformer ?
Most broadband linear solid state HF power amplifiers are designed for
50 ohm input and output impedances. Thus, with 50 W of power, this is only 50 Vrms.To get to 300 Vrms, a step up transformer would be required, but due to the narrow frequency range, a conventional transformer design should be sufficient, otherwise 1:4 and 1:9 transmission line transformers might be cascaded.
Some amateur radio solid state linear HF power amplifiers in the
100-600 W range might also be sufficient.These are typically designed for intermittent operation, so the heat sink is not sufficient for continuous operation on nominal power, but the larger one should be able to operate continuously. Driving the amplifier below full power, will usually improve linearity.
Depending on the output level in your signal generator, an intermediate amplifying stage might be needed between the generator and the power amplifier (which typically needs something like +25..+35 dBm drive power.
Yes, I was considering that, with something like the ENI 2400L amp:
The 400W output through a 1:9 transformer would no doubt provide the desired 50W at 300V.
The intended purpose is to drive a plasma antenna., which is obviously a non-linear load.
Since you seem to be on top of the game, do you have any suggestions about coupling to this, via the transformer, and protecting the (expensive) amp from back EMF, overloading, etc?
Many thanks for your advice so far..
Jim Clark
(not upside down to you)
A 100W amp would just be loafing at 50W, even continuous sine wave. And spec a 75 ohm output; that way you can use a 1:4 balun for your 300V.
Cheers! Rich
The amp you describe would output a few volts at 100W. To get 300V after a step-up transformer at the _same_ wattge, I believe the rated wattage of the amp would need to be increased proportionately. Or do I have this wrong?
Jim Clark
You've got it wrong. Transformers aren't all that lossy, and power is just voltage times current. The transformer steps up the voltage and steps down the current in the same proportion.
-- Bill Sloman, Nijmegen
I am sorry, I could not make any sense of your figures.
The OP wanted to drive 50 W to a load with a 300 Vrms swing. Thus the current would be 167 mA and represent a 1800 ohm load.
An RF power amplifier delivering 50 W to a 50 ohm load will produce a
50 Vrms voltage and 1 Arms current. To get this to the previous load specification, a transformer with a turns and voltage ratio of 1:6 is required. This translates to a 1:36 impedance ratio.If a transmission line transformer must be used, the 1:36 impedance ratio is not very practical, a more practical approach is one 1:4 stage followed by 1:9 transformer.
I would not expect that an amplifier with anything less than 100-200 W (nominally) for intermittent amateur service would survive in 50 W continuous service for any longer periods of time.
Even if you could find a 100 W (continuous) into 75 ohms (I do not think cable TV used such distribution amplifiers :-), this would only produce 87 Vrms, using a 1:4 balloon would produce 173 Vrms into 300 ohms.
Solid state RF amplifiers usually have some kind of SWR (reflected power) protection, cutting off the input signal, if the reflected power is too large. I have no idea how a plasma antenna behaves, but if there is a transmission line segment (either as a long coaxial cable or some lumped inductors and capacitors), any load would like mismatched transmission line and hence the SWR protection should work.
No, it's already been stipulated that there are amps available from
100 to 600 W output. And 100W at 75 ohms is more than just a few volts.Yeah, I kinda figured that those who were following the thread would know that it would need to handle 50 watts.
Only in that the amp wattage was the first thing they called out.
Hope This Helps! Rich
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