Tube Suggestions Onix SP3

As a rookie to tubes, one of the Melody 5881s tubes on the Onix SP3 I recently purchased on Agon has gone pzzzsst and I'm clueless and suffering without good sound. I have to keep within a reasonable budget but at the same time have a solid replacement for resale value. Can the original Melody 5881's be had anywhere? Otherwise the tube shop I called said I need to replace all four, rather than only 1 and recommended the NOS Sylvannia 5881 at nearly $90 per. I'm tempted to just buy another used Onix if that's the case. (Just kidding) Help
I received the SED 6L6GC tubes and installed. On immediate listening they seem much more harsh on female vocals than the original Melody tubes. Almost to the point of sounding like clipping. Could this result from no burn in time yet? It was as if I hooked up an inexpensive receiver, nothing close to the original sound. Do I need to change some settings on the Onix? I've heard others talk about bias but not sure if this is possible on this Amp. (No Manual came with it) Any suggestions would be helpful.
Power tubes usually do require break-in. I've frequently found that the top smooths out and the bass developes after 24 to 100 hours of operation, BUT.....

Proper biasing is manditory and the bias setting for the 6L6's would be quite different than the 5881's. I'm not up to speed on the bias arrangement for the Onix but if its not auto bias (as I suspect) you should contact the distributor, referred to earlier, and find out how to bias in your new tubes.
Hey get2it1 - the SP3 is not an autobiasing amp, you need to re-set the bias whenever you replace the 5881s. Technically the 6l6gc is not a direct replacement for the 5881 and needs to be biased higher than the 5881. The 5881 bias should be set a 1.15V. Some fellow sp3 owners on the av123 forum calculated the 6l6gc tube bias as 1.60V for the sp3. When I put in my 6l6gc I just biased it at 1.15V with the plan of increasing up to 1.60 but I never got around to it because it sounds good at 1.15 and I figure I'm stressing the tube less.

As for actually biasing the unit you need to get a voltmeter if you don't own one already. You can pick up a digital voltmeter at Radioshack for under $20. Turn your system on and let the amp warm up for 5 minutes or so. Don't play any music while you are biasing the amp, this is important. On each side of the amp you will see 5 holes. Turn your meter on and insert the black lead into the center hole. Insert the red lead into the hole on the far right and check the meter for a reading. Insert a small screw driver in the hole between the leads and turn the screw until the bias reads 1.15V. Once this is done remove the red lead and insert into the far left hole and then adjust the screw between the leads until it also reads 1.15V. You've just biased the two tubes on the side of the amp. Repeat the procedure on the other side and you're done!

One thing to remember is that these tubes take about 24hours of play time to break in and during that time the bias will often drift so you may need to reset occasionaly during this break in period. After this breakin period you should only need to check the bias every 6 months or so.

Good luck!

Go to the following forum thread and you'll find some great information on biasing the Onix SP3 amplifier:
Outstanding Tooter, Rhing and Newbee. Left a message with av123 checking on the replacement Melody as a plan B. I will work on the Bias per your instructions Tooter. Much Appreciation All.