Ok so firstly, yes i did do a search but didnt realllyy find my answer.

So whats going on is, in the absense of an attentuator (buying one in the next few weeks) when i got my amp back from being repaired, i go 2 of my power amp tubes pulled so i could pump the tubes a bit harder (i think it sounds way better... except for cleans... theyve gone to the ... bin? can't swear here.) and i was wondering, my head (bugera 333xl) has a switchable impedence on the back which the guys at the store set to 8 and said leave it. Now i have a behringer stack (yes.. i know.. crap.... until i put celestions in it which wont happen for another 6 months, but bear with me.) so this amp has a 16 ohm and 8 ohm setting (mono and stereo) and i was wondering what it should be set out seeming as the tubes have been pulled and all that jazz.

it SEEMS to sound better when i put it on stereo... but i dont wanna blow up my head or cab... again... so any advice would be great.
With two tubes pulled, run it on the 8 ohm setting into the 16 ohm setting (mono) on the cab.
Sweet... i dont suppose you would know why my power amps are humming like mad (i stick a noise gate in the FX loop and its still there so its inbetween the power tubes and speaker) coz i tried diff cables and its still there.... easy enough to get rid of in recordings (invert the phase of a recording of the hum) but it doesnt change volume no matter what i do to the amp.
Sounds like bad power tubes, or something wrong with the power supply.
Try switching out the two power tubes in there for the two you're not using, see if that helps.
I would... but im not 100% comfortable with playing around with things like that. Do you think it might be coz its only running off 2 tubes?

Can i just change the tubes without having to rebias? I bought them as a matched quad.
Last edited by doommaker at Oct 10, 2008,
u can switch them but switch them accordingly, meaning if u have 1 and 2 in now put in 3 and 4....u get what i mean...and i really think u should invest in an attentuator cause eventually ur either gonna **** up ur tubes or gonna need to learn to bias them to keep them cool...also i really dont know what to say about the impedance...i think it should be the same as only the wattage changes when u pull tubes...the power amp should need the same impedance as before but i cant promise u this.