Marshall Super Bass preamp tubes

[KillerV]

I've had my Marshall Super Bass for a while now and it's a killer amp, but I've found recently that it hasn't been sounding as great as it always did. The amp also breaks up at even the cleanest settings. Am I right to assume that this means my preamp-tubes need to be replaced? If so, what would be good replacements for playing hard-rock and blues? A guy whose opinion I trust suggested that I try Electro Harmonix 12AX7's. Are they any good?

One more thing that I've noticed is that there's a strange almost "tremelo"-ish type of thing happening when I play the open A-string on any of my guitars. It also happens when I play the same A (5th fret) on the bottom E-string. It only happens on the low A's - no other notes. Does this also have to do with the worn preamp tubes?

[donnyjaguar]

By first approximations it sounds like your amp is biased too hot, drawing too much current, overworking the power supply and causing this condition.

I won't comment on the various "tonal" qualities of 12AX7 tubes. Plenty of experts here when it comes to that kinda thing.

[dk123123dk]

I've had my Marshall Super Bass for a while now and it's a killer amp, but I've found recently that it hasn't been sounding as great as it always did. The amp also breaks up at even the cleanest settings. Am I right to assume that this means my preamp-tubes need to be replaced? If so, what would be good replacements for playing hard-rock and blues? A guy whose opinion I trust suggested that I try Electro Harmonix 12AX7's. Are they any good?

One more thing that I've noticed is that there's a strange almost "tremelo"-ish type of thing happening when I play the open A-string on any of my guitars. It also happens when I play the same A (5th fret) on the bottom E-string. It only happens on the low A's - no other notes. Does this also have to do with the worn preamp tubes?

Have the caps ever been replaced? If that is a vintage head, it could need a checkup. EH tubes are decent for new production, but I think I would go with a nice NOS ecc83 in there. I would have a tech check it out.

dk

[JimmyR]

I would be more likely to suspect the power tubes. However preamp tubes can be inexpensive to try replacements. EH 12ax7s are ok - fairly full and fat sounding but not particularly spectacular. I would suggest trying them or JJs in the second and third positions, but if you can afford it get a good NOS Phillips or Mullard or similar for the first position (furthest from the power tubes).

As for power tubes, I like SED ("WingedC") EL34s but have recently been using JJ KT77s in my Marshalls. The JJ KT77s bias up just like EL34s and sound great in my amps - just like a really good EL34. I think it is more likely that it is the power tubes that need replacing. Modern power tubes often only last a year or less of constant playing.

If your amp is an original then yes check the filter caps also. They're the big blue-plastic (sometimes green) things poking out the top next to the tubes. If replacing them I strongly recommend getting good quality caps like F+T or JJ from somewhere like metroamp.com. Don't worry if they're a bit shorter than the originals!