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Author Topic: Will New Power Transistors End the Need for Tube Amplifiers in the Future?  (Read 22536 times)
WX2S
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Posts: 744




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« Reply #60 on: January 24, 2013, 02:25:34 PM »

If only he'd build some for HF...

- WX2S
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73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
G3RZP
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Posts: 4830




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« Reply #61 on: January 25, 2013, 12:58:53 AM »

That one is not linear, which is why it gets that efficiency.

But 'harmonics CCIR'? CCIR ceased existing 21 years ago.......

It SHOULD be to ITU-R SM329 or for Europe, ERC/REC 74-01.

Doesn't say much for a company that can't state the correct applicable standards.

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NO9E
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Posts: 433




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« Reply #62 on: January 25, 2013, 01:38:45 PM »

The info is at http://cache.freescale.com/files/rf_if/doc/data_sheet/MRFE6VP61K25H.pdf?pspll=1

According to curves, at 2.4 A standby current the efficiency is 62% at 700W, 72% at 1000W and 80% at 1.3 KW. Highest power with some overdriving but why not on CW.

IMD3 about -32db at 1 KW but < 40db at 700W. Probably easy to improve with minimal feedback.

The clue to efficiency is tuned and not broadband network. One MRFE6VP61K25H costs about $200 in quantity. Probably one can afford a few with different one for each frequency range.

Ignacy, NO9E

That one is not linear, which is why it gets that efficiency.

But 'harmonics CCIR'? CCIR ceased existing 21 years ago.......

It SHOULD be to ITU-R SM329 or for Europe, ERC/REC 74-01.

Doesn't say much for a company that can't state the correct applicable standards.


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W6TVK
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Posts: 25




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« Reply #63 on: January 26, 2013, 11:29:02 PM »

RZP:  I'm surprised that nobody has come out with liquid cooled solid state modules!

That would be an intersting concept.

Harris sells solid state TV transmitters whose RF modules are water cooled.  The heat spreaders have a serpentine copper tube on the back side that carries a glycol coolant solution.  In the unit I know about, we get about 500 watts output per module in the UHF TV band. It's great design that works very well. 
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M0HCN
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Posts: 473




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« Reply #64 on: January 27, 2013, 09:07:29 AM »

I have built liquid cooled solid state amps (mainly for RF plasma drivers), and there are a few issues that do not appear in air cooled units to anything like the same extent.

Condensation will get you if the amp is in a warm room and the radiators are outside, and you need to provide flow fail cutouts and the like, leak detection is a good idea.
Even if most of the heat goes into the cold pate you still usually require air to cool the incidental bits (power supplies, magnetics, caps, resistors, also the output filters will need cooling air), so you usually end up with a fan anyway.
 
Remember also when looking at those efficiency numbers that those amps are tweaked to deliver into 50 ohms resistive, an amateur service amp is usually expected to deliver into 1.5:1 VSWR so needs a drain match that will deliver rated power into 75 ohms, that hurts efficiency into 50 ohms, there is a way to fix it, at the cost of more power supply complexity and a more sophisticated impedance bridge at the output.

I have contemplated playing with that freescale part, but as the UK limit is 400W at the aerial there is limited point in me going there.

73, Dan.
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