Help me diagnose an amp issue

Jaek-Chi

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Hi all,

Just wanted to get a bit of advice to see if this was an easy fix or if it sounds more problematic and would require getting a tech to look at it. I've gone through a heap of amps and honestly i've been pretty lucky in the sense most have been problem free.

Went to play my Engl Savage the other day, turned the power on, it warmed up for about 10 minutes, i plugged my guitar in, and took the standby off. It made a loud popping noise, which sounded odd. I then strummed a few notes and it was fine for probably 3 seconds, which it then cut out all response and made a constant noise that was louder than the tone coming through for the brief time it was working. It wasn't feedback, it was similar to when you put your lead into your guitar while the amp is on and its not all the way in the guitar jack so it makes like a constant thick, loud humming (?) noise.

I switched the amp straight off. After an hour or so i pulled the back cover off. All the tubes seemed to be ok, and i also checked the fuses at the power supply point, which also looked ok. Unfortunately that's about where my knowledge stops

Any ideas what it could be?
 

wakjob

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It's a tube amp.

First step, check all tubes...
 

Jaek-Chi

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Yeah i had a look at all the tubes. They seemed to be fine. No sign of the filament being damaged or black, blown tube. I'll have to have another look though.
 

glpg80

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Looks mean nothing. Pull the preamp tubes out one by one and check them with a known working tube.

Check the power tubes by pulling the outter pairs and halving the impedance of the amplifier. Check to see if the problem leaves. If not, replace the ones you pulled back into the amplifier and pull the inner pair. Check to see if the problem leaves.

If none of the power tubes remove the problem, put the impedance back to normal.

Power tubes rarely go in pairs, so it will be 1 of the 4 power tubes if they decided to let go. If it is a bad power tube, you're taking it to a technician which can verify other parts are not damaged like arcing across socket pins, bad screen grid resistors, internal fuses needing replaced or checked, bad switches, etc.

If it's a bad preamp tube then you simply pull each tube one by one and replace it one by one until you've found the culprit. No impedance or biasing anything to worry about with pres - just never hot swap them.
 


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