What's wrong with my MOD-50 - update: bad EL34 power tubes

  • Thread starter Thread starter MkIV
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MkIV

MkIV

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I plugged in my MOD50 today after not having used it for some time. Started in the Low power mode and it sounded very strange - Ok when I hit the strings but sounded rasping as the tones faded out. I turned it off and switched to Hi power and the sound was ok again. But after a few minutes it started to sound almost like if I were using a tremolo and the volume slowly decreased. The problem remained regardless of which module or channel I played with.

I haven't done anything yet, but I'm going to swap the power amp tubes later tonight. I think its a pair of Groove Tubes EL34's in it right now. Think I might switch to a pair of 6L6 or 6V6 for starters.

Any other tips on what might be the trouble? Perhaps I should check the phase inverter tube as well? :confused:
 
If it's on every channel,could be the power tube only.Should be all right with new power tubes.Good luck!
 
How does the quote go.... if it's a tube amp, 9/10 it's the tubes that failed.

I'd assume it's one of the tubes in the head....check the tubes are all seated correctly then check the bias and tube failure lights......my guess would be it's a Power Tube failure or the 12ax7 in Phase Inverter slot (immediately adjacent to power tubes)

no go there try a known good 12ax7 one at a time, starting at v1 (closest to the input)
 
Yeah, it sounds most logic that it's either the phase inverter or a power tube.
 
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