Power tube, Speaker, Output Transformer issue?

[bkemp23]

I replaced the power tubes in my Wizard MCII about a month ago without issue. Yesterday, my amp started to sound terrible, missing low end, the low end that was there was farty, overall kind of fuzzy sounding. My measurements from my original tubes were 486VDC and 32.2mADC. Those were the values I set for the new tubes. After rechecking the bias once the amp started to sound like crap, it was now measuring 501VDC and 28.7mADC. I checked the resistors around the tube sockets and they are all within spec. Bad tubes???

Also, when I was playing, i noticed my speaker was starting to smell funny, no issues prior to this. Was that just from the farty bass or did i somehow damage the speaker, possibly something wrong with my output transformer? it is a WGS12L so no way it should have been getting over powered. Also, it is only a week old so did I get a bad speaker???

Anything else I should check?

Thanks in advance.

 

[glpg80]

You have to burn in new tubes and monitor their bias range over the course of 24 actual on-time hours before they settle to a specific value.

The original loss of bass and overall tonal suffering is already right there in front of you - you blew your speaker.

Bad power tubes have popping and crackling sounds as well as a loss of definition of lows and highs, but not to the point that it won't function correctly when biased correctly.

Note that as plate current goes down indicated by your bias, plate voltage will go up since tubes at idle aren't pulling it down. You'll have to calculate your 60% threshold using around 480V from the prior known working tubes and not the 501V value of the new tubes not yet burned in.

When you suspect something bad has happened, the finger points to the latest changes you've made: either the speaker or the tubes.

Hopefully once your tubes are biased correctly the problem will still be around and you'll be able to point the finger to the speakers. If the problem resolves itself with the bias, then you'll know it wasn't the speaker - albeit you're going to likely need to replace it anyway as the voice-coil is compromised if you smelled the coil burning.