Off Topic Strange problem with a Marshall DSL 401

[fbecir]

Hello

I have a strange problem with my Marshall DSL401. I bought it new 5 years ago and I played a lot with it (rehearsals & gigs).
2 months ago, it started to behave strangely : the Clean Channel lost some power (in order to play at the same volume I have to increase the master volume) but the Dirty Channel still behaves normally. Besides, there is now a noise with the Clean Channel at high volume.
Thus, I thought it was time to change the tubes. I bought some new 12AX7 (SOVTEK) and new EL84 (Groove Tube). It did not solve the problem.

So what's wrong ?
Another clue : after one hour of playing, the Clean Channel starts to behave normally.

Any idea ?

Thanks for your help

 

[TNT]

1. Heat was an issue on the earlier models, and caused those very symptoms. A fan will help, or just open it up a little more in the back.

The later models didn't have the same heat issue, but also did not sound the same (certainly different, and not as good in my opinion!).

2. If tubes were just replaced (and biased correctly, extremely important with this amp), then check transformer.

By the way, the power tubes are the "small diameter" tube type, did those
GT's fit in there easily?

 

[fbecir]

Hello TNT. Thanks a lot for your advices.

My DSL 401 is from December 2003 and I believe it is the second generation (thus without the heat problem).
For fitting the tube, there is no problem with the EL84 from GT. The only problem you have is with the 12AX7 : the Marshall ones are thin and there is a rubber ring to protect the tube. The SOVTEK are bigger thus is not possible to use the rubber ring. It seems that it's not a problem.
For biasing, most of the amps are biased on the cold side. Thus the factory biasing is not optimum but should not be a problem.

The thing that puzzle me is the fact that when the amp is really hot (after 30 minutes), it starts to function perfectly. If a component was out of order, this should not happen

Thanks again for helping

 

[candid_x]

Might try another (and a better) 12AX7 than Sovtek in the V1 position. The V1 is hugely responsible for shaping your amp's clean tone, and everything that follows in the signal path. Might try a straight JJ 83S or EH in there, or the new Tung Sol reissue might even work best for that amp. All current production and readily available. The Sovtek 12AX7LPS isn't bad, high gain, but the WA's are just plain ratty sounding, imo. That's the first thing I'd replace to trouble shoot the amp.

 

[Spudmurphy]

I would recommend that you contact Marshall - they are a great company to deal with.

If you could get to their factory they would sort it out for you.

 

[colinboy]

I too have this amp but havent had any problems with it so far.maybe it over heated or something like that???

 

[rickjohns]

I have owned several of these amps, and also own a DSL100. Marshall is notorious for poor soldering on the circuit boards. You might have a cold solder joint, and when the unit heats up it makes better contact. I would take it to a tech, and have them go over the boards and resolder everything. I have had this done to all three of my marshalls, and they have been rock solid reliable ever since.

 

[Larry]

I have owned several of these amps, and also own a DSL100. Marshall is notorious for poor soldering on the circuit boards. You might have a cold solder joint, and when the unit heats up it makes better contact. I would take it to a tech, and have them go over the boards and resolder everything. I have had this done to all three of my marshalls, and they have been rock solid reliable ever since.

My suggestion as well.

 

[DrGonzo5150]

I have owned several of these amps, and also own a DSL100. Marshall is notorious for poor soldering on the circuit boards. You might have a cold solder joint, and when the unit heats up it makes better contact. I would take it to a tech, and have them go over the boards and resolder everything. I have had this done to all three of my marshalls, and they have been rock solid reliable ever since.

+1

Can't stress it enough. It's a must!!!!
Ultimately I ended up having circuit boards resoldered in all my amps.
And same as above..
Rock solid reliable ever since.

 

[fbecir]

Thanks a lot for your answers

I believe you are right concerning the problem of my poor DSL401 : a cold solder joint.
Spudmurphy : I really would like to visit the Marshall factory, but I have to cross La Manche (you call that the English Channel ), but here in France I have to deal with the distributor.
I know a guitar & amp tech near my home. I think I will call him. What will be roughly the price for such a reparation ?

Thanks again for your help

 

[Spudmurphy]

Jump on the Le Shuttle and you'd prolly get there quicker than me ha!

No seriously, if you did cross La Manche to spend a couple of days here you could arrange a trip around the Marshall factory and get your amp fixed at the same time. It happened when I was a there - a guy dropped off his amp and a couple of hours later he called back for it and it was sorted.

Is your amp made in the UK?

 

[fbecir]

Jump on the Le Shuttle and you'd prolly get there quicker than me ha!

Yes that's true ! I like to travel by train but with a 22kg amp it's a bit harder
For visiting London, it's really nice (3 hours from Paris).

Is your amp made in the UK?

Of course it is !
I believe that all the tube amps are still made in Bletchley. For me a real Marshall is made in UK ,a real MusicMan is made in USA and a real Camembert is made in France.

 

[Spudmurphy]

It's just that I know that certain models of Marshall are made abroad. - prolly the solid state ones.

I wonder why the soldered joints are breaking down as people have indicated in this thread.

When I saw the assembly line at the Marshall factory, the circuit board was prepd with it's components and checked "dry" (unsoldered) for continuity.

The circuit board was then pre heated before it went for a bath in the "solder pool" - meaning that no human did any soldering and being brought up to temperature meant that it wasn't "shocked" as it entered the hot pool. If the board doesn't suffer from dry joints where are the location of the dry joints? - to the valve bases?

 

[candid_x]

I believe that all the tube amps are still made in Bletchley. For me a real Marshall is made in UK ,a real MusicMan is made in USA and a real Camembert is made in France.

LOL! Vive le Camembert!