Blown HT Fuse, Uber Rev 2 - Update: Biasing Questions

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russellconner
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After blowing the HT (1A, slow blow) fuse a week or so ago, I replaced it and the amp has been running fine. However, to be safe, I checked the bias last night.

The bias ranged from 31 mA to 38 mA across the four tubes :scared: , so I lowered the bias so that the tubes are now all between 27.5 mA and 33 mA. I didnt check the plate voltage last night, but when i put the tubes in a year or so ago, i believe it was 498 V. So, this puts them at 55% to 66% dissipation.

The sound seems fine, but i havent pushed them very hard yet.

something im hearing, and maybe its just an E34L characteristic, is the sound getting "congested" when i crank up the presence on the dirty channel. it sounds like its overwhelming the power amp. with the presence down, it sounds much more clear and defined.

also, just for my reference, at what gain/presence/channel vol/master vol settings do you reach a point where the amp is maxed out and starting to break up?

when i have the gain at 2:45, presence at 12:00, channel vol at 11:00, and master at 1:30, it sounds very pushed and about to break up...if i increase the presence, at these settings it sounds like its going to catch on fire. how about you guys' settings?

the reason i ask, is this amp has never seemed to have the air-moving capabilities of my '94 dual rec. now, to be fair, the dual rec vol taper is brutal. its holy smokes loud at 11:00 (channel vol, i dont use the effects loop/loop active master). beyond that, it starts to break up and not add volume.


sorry for all the questions, but thanks anyway in advance for any input you guys might have.

russell
 
You should be fine, although it seems that JJ power tubes have a lifespan of about a year when playing at high volumes, so I'd keep an eye on them. You might also want to check for bias drift, and you probably already know that the hotter you bias the tubes, the shorter they're gonna last.

As far as the fuse, it should probably be fine if you replaced it with the correct type.
 
Please see updated info/questions in original post.

thanks,

russell
 
When I had JJ E34L's in my Rev Blue, at about those settings it seemed that there was an immense amount of power tube distortion and it just seemed to flub out. The Winged C's in my Rev 2 don't do that, so it might be the JJ tubes which have been known to have QC issues at times. Lowering the bias is going to reduce how quickly the power tubes are going to distort. IIRC those tubes you have are pretty old, so it may be that they're starting to wear out.

My advice would be to retube it with better-matched power tubes. That may solve your problem of power section distortion and volume loss.
 
 
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