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Author Topic: my qro lost its power, from 110W down to 18W  (Read 1895 times)
SINDK8
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« on: October 23, 2004, 03:57:40 AM »

its a sad story, its a tpl, 5 watt in, 110 out. linear amp. i accidentally keyed my transciever, high power(45W)for about .3 seconds. I immidiately i put it on low power (5W). theres no smoke, no foul smell. the only evidence it left was in the in-line wattmeter reading. reading just 18Watts. not just like 110W flat. i inspected the relay, the diodes, the transistors and i didnt found anything unusual discoloration or any burn marks. it still clicks, but only 18Watts. I am worried. I know, its my fault. i am very sad now. BTW, this qro has 4 MRF224 transistors installed. is there any datasheet available on this motorola transistors. please help me.
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K6AER
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« Reply #1 on: October 23, 2004, 10:40:25 PM »

The MRF 224 transistors will not handle the 45 watts excessive power even for a second. That amplifier design has only three transistors in a parallel design. The good news is the transistors are about $20 each and can be removed with a soldering iron and solder wick.
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SINDK8
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« Reply #2 on: October 25, 2004, 03:44:56 PM »

whew, are these mrf224 transistors available in the market?, coz i searched the internet, i cant find any datasheets related to this transistor. do you have a service manual of this tpl qro, and yes youre right it has 3 parallel transistors and one pre driver, all the same mrf224. Smiley
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KE3HO
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« Reply #3 on: October 26, 2004, 10:26:54 AM »

http://www.rfparts.com/mototran.html

There are probably other sources too.

73,
Jim - KE3HO
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W9GB
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« Reply #4 on: November 02, 2004, 06:38:54 AM »

SINDK8 -

You may be lucky and have only lost some discrete components on the input side of this amplifier, BUT unless you are have good soldering skills and sufficent knowledge to test the trasnsistors with a VOM -- you could easily waste time ($$/hour your labor) and spend $$ for parts that you really would not need to replace.

IF this is an educational project, then I would highly suggest a bit of reading [Motorola Application Notes - authored by Helge Granberg(sk)].  These are available at the CCI web site.  Application notes AN791 is close to this design - CCI kit number 875

RF Parts will have these transistors and alost every compnent that you woudl need.  THey also have some of the Motorola application notes on file.

w9gb

w9gb
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