Rf power amp testing

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Blackolive
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Rf power amp testing

Post by Blackolive » 26 Apr 2019, 12:58

Picked up an 140 watt 2M linear for silly money.
It was advertised as non working.

I know that the transistors can be tested with a multimeter and measuring across the junctions, but due its method of construction its not going to be easy without possibly damaging the Unelco caps.

If they have failed, do they normally fail open or short circuit ? Im hoping I can do initial testing around the RF circuitry by firstly checking the resistors particularly around the biasing circuits, then putting it on a current limited supply and measuring the voltages at various points.
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Blackolive
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Re: Rf power amp testing

Post by Blackolive » 26 Apr 2019, 12:59

Pics
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Blackolive
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Re: Rf power amp testing

Post by Blackolive » 26 Apr 2019, 13:00

Made a start on the cosmetic side
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dt307
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Re: Rf power amp testing

Post by dt307 » 26 Apr 2019, 15:13

i norm fit swr meter before and after if it goes off the scale the trannies are bad and i remove them and check them with a tester not a dvm .
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Blackolive
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Re: Rf power amp testing

Post by Blackolive » 29 Apr 2019, 10:34

good shout

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Re: Rf power amp testing

Post by Blackolive » 05 May 2019, 13:15

Nothing is screaming popped transistors (yet) so Ive tidied it up, changed some drifted components and caps, and got rid of all the old flux residue.
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Blackolive
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Re: Rf power amp testing

Post by Blackolive » 17 May 2019, 08:32

It lives.

Not tried it at full power yet as I hadnt put thermal compound on the transistors. Ive fitted a small computer fan as some of the parts inside that get warm arent heatsinked. Tidy job. Going to use it with an IC-251 with mutek front end, should be a decent station

https://youtu.be/Dy_cqqq89xI

https://youtu.be/WT7t1fq6Kc8
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