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Minipa100 parasitic oscillation - help?

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bob edwards
Posts: 9
Joined: Sun Feb 14, 2021 9:34 am
Location: Chippenham, Wilts, UK

Minipa100 parasitic oscillation - help?

#1

Unread post by bob edwards »

Trying to set the standing current at 1A on this amplifier kit. At about 240mA, the current rises uncontrollably to 8A. Temporarily connecting a diode detector to one of the transistor drains it detects 65v dc - oscillation. I've terminated input and output with 50 ohm.
Has anyone found a fix for this please? The board and circuit are like this one https://www.aliexpress.com/i/4000970169145.html

Like others, I'm considering replacing the MRF9120 dual vhf mosfet with a pair of IRF530. Less power and hopefully more stability. It'd be nice to get it going as-is.

Cheers, Bob G4BBY

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