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Author Topic: KW amplifier with MRFE6VP61K25H in production for 2m  (Read 6270 times)
NO9E
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Posts: 711




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« on: February 15, 2012, 06:19:10 AM »

There was a discussion on  MRFE6VP61K25H a while ago. Lots of doubts including the reliability.

Looks like the device is used now commercially for 2m: 2 W in  1 KW out. This is key down not pulse mode; see http://www.w6pql.com/parts_i_can_provide.htm

Since he offers it for sale he must have done lots of testing and determined good reliability. He also sells a module for $790, which is not much more than a 3cx800. His thermal design is interesting: the module is soldered to a copper plate.

If one is CW operator, such a device used in KPA500 can increase the output to some 800W due to increased efficiency (70 vs 45%) and could be driven by K3 in low power mode. Not sure whether linearizing with this module would be easy. 
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KH6AQ
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« Reply #1 on: February 15, 2012, 06:50:30 PM »

I believe the apparently low efficiency of HF linear amplifiers is due the fixed output impedance matching network. In order to provide rated power at a VSWR of 1.5:1 the matching network is designed to do so at 75 ohms (where maximum efficiency occurs). Into a 50 ohm load the efficiency drops.

So, if an amp is designed to have an efficiency of 70% into 50 ohms it will not be able to supply as much power into a 75 ohm load.
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NO9E
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« Reply #2 on: February 15, 2012, 07:21:31 PM »

This module is rated at > 70% efficiency. MRF150 is rated at 45%. Must be not only due to class C in the former but probably also due to a different matching.

But it seems it if something is possible on 144 MHz it must be easier on lower frequencies.

Ignacy
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N3OX
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« Reply #3 on: February 15, 2012, 07:29:38 PM »

There was a discussion on  MRFE6VP61K25H a while ago. Lots of doubts including the reliability.

Looks like the device is used now commercially for 2m: 2 W in  1 KW out. This is key down not pulse mode

Were the "doubts" about that video where the device is putting out almost no average power while running off a current limited power supply and it's shorted out with a screwdriver proving how "rugged" it is?

I think many transistor modules will be very, very reliable if you supply them with the appropriate high VSWR shutdown and other monitoring and protection circuitry.

But you still have to do that protection stuff, even for the devices that have Youtube videos showing some dude shorting the output with a screwdriver.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KH6AQ
Member

Posts: 7718




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« Reply #4 on: February 16, 2012, 06:09:10 AM »

This module is rated at > 70% efficiency. MRF150 is rated at 45%. Must be not only due to class C in the former but probably also due to a different matching.

But it seems it if something is possible on 144 MHz it must be easier on lower frequencies.

Ignacy


So you are comparing apples and oranges. We don't want a class-C ampllifier on the HF bands even for CW. On CW it will distort the CW element rise/fall times (decrease the risetime) and cause key clicks.

Now we will run this new transistor class AB on HF. And let's set the matching network to provide rated power to a VSWR of 1.5:1. What DC-RF efficiency do we get? About 45%, the same as the MRF-150.
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KH6AQ
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« Reply #5 on: February 16, 2012, 08:51:09 AM »

It is possible to achieve very high amp efficiently at least on the lower HF bands. In 1993 ssing a power supply MOSFET I achieved 90% efficiency at 7 MHZ counting driver stage power. The output stage alone had an efficiency of 90%. Note that the output power was 25 watts.

The amp was very far into class-C with current rise/fall times of 5 ns. To meet amateur harmonic regulations a five pole output filter and matching network was used. And to amplify CW while retaining the rise/fall of the input RF envelope audio feedback was used. So, during the rise/fall times the efficiency suffered.

Amps like these (high efficient class-C) are used for industrial processes such as AC plasma etching and deposition.
« Last Edit: February 16, 2012, 09:19:08 AM by WX7G » Logged
WB8VLC
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« Reply #6 on: February 18, 2012, 01:43:36 PM »

I wouldn't recommend buying any amps for SSB that are using the 1kw part due to poor IMD, if they were using a pair of the 600 watt parts then yes by all means but the 1KW part is supposed to be getting a die change which will addresses the IMD problems.

So far I haven't heard anything on when the changes will be finished, but I'd wait a couple of  months to see if the part number will change entirely or just how Freescale's going to differentiate the improved parts from older ones.

Mike
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