• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

amp troubles

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this is my first tube amp build. i found the schematics at http://www.ax84.com/moonlight.html. when it worked i was happy how it sounded (althougth it didn't have much tone control). but now whenever i turn the amp on it makes this pulsating popping sound (like a machine gun). when i first power up and strum the guitar i hear audio for a second then the pulsating noise starts up again. i don't see any burnt components. could it be a bad tube or power supply. please someone help me.
 
I agree with SY's idea; The trouble is most likely instability due to a supply decoupling inadequacy.
Next, check that all decoupling parts (3 electrolytics) are connected properly. if so, then maybe one is faulty. Try adding another in parallel across each in turn. :att'n: Observe polarity and watch out for stored charge.:att'n:
 
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