#1
I have a Marshall DSL401 and it's my first Valve amp. When I played it the other day it just didn't sound 'right' and the clean channel didn't have the volume I expected. Does this mean that the valves need replacing? If so, will I need someone to do it for me as my technical knowledge is very limited and what sort of valves should I look at for it? At the moment all I know is that the valves currently in it are JJ Tesla.
Gibson Les Paul Studio with Catswhiskers pickups
PRS SE 'Floyd' Custom 24 with Creamery pickups
Fender Standard Stratocaster with DiMarzio pickups
Takamine GN30
BluGuitar AMP1
#2
What about the disti channel?

If it has a loss in volume too I would say you need power tubes. If it is just the clean channel then it is possible you only need a new preamp tube or two.

If you like the current tone you have stick with JJs. If you want to change your tone at all you can look into a different brand of tube.

Can't speak to whether or not you will to bias the amp when replacing power tubes as I'm not familiar enough with it. My guess is yes, in which case get some help.

Preamp tubes you just pop in and play.

Does that help?
#3
That does help a bit actually. I noticed the loss of volume on the clean channel most as the master volume is always maxed out and when I switched to the clean channel I wasn't suddenly deafened. What I noticed on the drive channels was a partial loss of volume but mostly a bit of a deterioration of tone.
Gibson Les Paul Studio with Catswhiskers pickups
PRS SE 'Floyd' Custom 24 with Creamery pickups
Fender Standard Stratocaster with DiMarzio pickups
Takamine GN30
BluGuitar AMP1
#4
I'd say get your power tubes replaced soon as they are on their way out. You may want to replace the last preamp tube, before the power tubes, while you are at it.

Maybe someone can tell you if this amp is fixed or cathode biased, I'm guessing it is fixed.
#5
The 401 is fixed bias.

A big difference in channel volumes usually indicates a preamp tube issue since the channels run on different preamp tubes but the same power tubes.
Those amps eat through tubes quickly, I'd suggest retubing the whole thing if the tubes are a few years old. When you're replacing the preamp tubes replace them one at a time and play in between so you know which tube was the bad one. Keep the rest of the tubes as backups.
#6
Thanks everyone but what does 'fixed bias' mean?

It makes sense to me to install a whole new set of valves but do you just remove old tubes and fit new ones like lightbulbs or is it rather more technical than that?
Gibson Les Paul Studio with Catswhiskers pickups
PRS SE 'Floyd' Custom 24 with Creamery pickups
Fender Standard Stratocaster with DiMarzio pickups
Takamine GN30
BluGuitar AMP1
#7
It is a bit more technical than that.

Yes tubes pop in and out, but they don't screw in like a light bulb.

Fixed bias means the voltage needs to be biased (think regulated) when you put new tubes in. Again, I have almost 0 experience in biasing Fender amps. The tubes work in pairs (in Class A/B amps) so they need their voltage 'regulated' once you put them in so work together the best they can. Otherwise, you could have a bias mis-match that could be harmful to the amp.

That said, most of the major tube distributors send tubes out that are Matched. This means that they have been biased already to match up. That doesn't mean you do not need to bias the amp once you put them in your amp.

I'd get a friend or a shop to do it for you. I could give you more information but I'm not really an amp tech. You would need a bias probe, multimeter and knowledge of electronics. For example filter capacitors store lethal amount of power and kill you if you touch one that has not been properly drained first.

PS: Some amps, like a Peavey Valveking are 'nonadjustable' fixed bias which mean you just pop the new power tubes in and play.

Some amps, like some Mesas, have test points and 'trim pots' built into the amp so you can easily bias yourself. Think of a trim pot as a knob that you turn to change the plate voltage. In most amps these trim pots are inside the chassis of the amp and better suited for an amp technician to work on.

Good luck.