changing tubes and changing amp bias

MLC2006

I think I want to change my tubes. I was reading that manual and it says that when changing to different tubes, sometimes the amp bias has to be adjusted. I don't know anything about this, but I'm fairly sure it's something I don't want to get into.

the amp is a Fender Blues Deluxe Reissue with stock groove tubes 3x 12ax7 and 2x groove tubes 6L6 (white).

what I don't like about the amp is:

1. the low end is too muddy
2. the clean channel starts to break up too soon at lower volumes. I would rather have crystal clear at as high a volume as possible and use a pedal for any overdrive. it is not a problem on the drive channel, just the clean channel when playing stuff like Skynyrd and Led Zep.


just from reading, I think I may want to try:

Tungsol 12ax7 and Groove Tubes (red). the red Groove Tubes are supposed to take longer to break down at higher volumes and the Tungsol are supposed to have very clear and crisp highs and lows. the reviews I've read on the Tungsols are pretty much rave reviews.

anybody recommend these or some other combination? would I have to have the bias adjusted in making these changes?

ianvomsaal

If you don't know how to bias, get it done by a tech - the voltage in an amp can literally KILL YOU!
Generally different makes of similar tubes actually read differently, which is why they have a rating. Typically if you switch tube
companies you'll probably want to get the amp biased just to get things running absolutely premium - which is why they make
different tubes - they all run slightly differently and thus it's why they sound different - you can completely change the tubes
out without biasing, but you'd be kind of defeating the purpose of changing the tubes, because the amp wouldn't necessarily
be running as optimum as it could. Changing tubes (same tube/same company) is fine to do without biasing, though if you use
your amp a lot it's a great idea to get you amp biased every couple years (because bias can drift a bit with heavy use). Then
there are some amps like Mesa that don't need to be biased - it's just how they're built - but if you put any tube other than a
Mesa Boogie tube in it you actually void it's warrantee, so if anything happens to the amp you're basically S.O.L.

exhausted

ianvomsaal wrote:

Changing tubes (same tube/same company) is fine to do without biasing, though if you use
your amp a lot it's a great idea to get you amp biased every couple years (because bias can drift a bit with heavy use).

they'd have to be matched tubes of the same grade to avoid having to bias.

but this is all moot for the blues deluxe. you can't bias it without monkeying with resistor replacement and on a pcb amp that's just asking for trouble. it's not an adjustable bias.

just get a matched set of tubes. hopefully your current ones are labelling with a number (groove tubes does this) so just get a pair of the same number and hope for the best.

do whatever you like with the preamp tubes. they're cathode biased so you don't need to worry about anything.

i'm not 100% sure how the clean/dirty arrangement works in that amp (i'm looking at the schematic but, despite building amps, i'm no expert). they aren't separate channels per se so whatever tube changes you make are going to affect both clean and drive sounds. it appears V1 is common and V2A (half a 12ax7) is added for the "dirty" but i'm not sure. look at V1 for changing your clean tone but it is going to impact the drive.

ianvomsaal

exhausted wrote:

ianvomsaal wrote:

Changing tubes (same tube/same company) is fine to do without biasing, though if you use
your amp a lot it's a great idea to get you amp biased every couple years (because bias can drift a bit with heavy use).

they'd have to be matched tubes of the same grade to avoid having to bias.

Yup, "same tube/same company" - same tube means same exact tube (rating included) - this means same everything.
If you have a GT #6 rating you'd typically have to stick with that (with the Fender tube scale, White = GT 4-7 range).
Hopefully this will help you: http://www.guitaramplifierblueprinting.com/Rating.html.