muddy low end tube amp syndrome

[Keven]

hey guys

i've been finding my quad el34 amp muddier and muddier these days in the low end. in full power 100w mode, it's fine, if a little rumbly, but on the low power 30 watt mode it's farty. i play differing guitars with bkp and not and it seems common

my first thought would be to replace the power tubes, but my amp isn't even a year old yet.

i called up yorkville tech support and he said mud means low power output. he told me it should be at around 25V or did he mean mV i'm not too sure yet, but the amp manual does state that tube biasing should be at 25mv give or take. could it be that my amp wasn't biased correctly when i bought it? it is still brand new but if only the bias is the cause of the farty low end that's been bugging me forever on this amp, i'd be happy to fix that!

so, does amplifier power output means the bias or is it something else?

[Twinfan]

Could be a couple of things I guess.  If it's under warranty, I'd send it back and get it checked out.

[jpfamps]

Could well be the power valves either drifting out of spec or on the way out.

The bias point of valves can and does drift with age so it could be that your valves have moved away from the optimum operation point.

Even though you've only have the amp for less than a year the valves could still be on the way out, obviously depending on the amount the amp has been used.

I suspect the valves won't be under warranty though.

[Keven]

another tech also said that electro harmonix tubes are pretty shoddy these days, and directed me to winged c for my power tubes and svetlana for the preamp tubes.

this amp has bias points and a bias trimpot, i could probably just re-bias is until i can get my hands on some tubes.

and you're right, the valves aren't under warranty.  i've played the amp every saturday this year for over 5-6 hours and in the summer we've had 3 rehearsals a week. so it's been used. but i bought it brand new.

anyway. i'll bring a DMM to band practice and check it out... thanks!

[Keven]

just another update i'd like to add to the mix. i was running my GT-10 preamps right into the tube power amp section of this amp (it's the YCS100H2 by traynor..) and noticed no muddiness or anything strange with this manner of working.

my local tech told me to check out the preamp tubes, as that could be the problem. and it kind of clicked, i noticed the muddiness when i ripped all my digital stuff out of my chain and plugged my guitar straight into the amp in 30w mode and went from there. that's when the muddiness showed its ugly face. since i noticed no muddiness with the gt10 and the tubes glow seem very healthy.. it could very well be it!

I'll start by swapping preamp tubes and go from there.