New DSL40C Odd Thump and Volume Reduction:

That got used regularly for 2 years,
Prior to my purchase of the origin
Then I paired the 2 together for a period, then I got the cobwebs off of my lead 100 mosfet,
And put it on vacation
As I have said never had so much as a hiccup with it !!
Cheers Mitch
 
Spent a few hours playing this last night - at volume levels a title less than 1/2 - and it acted strangely again but then cleared up and worked fine.

While playing, the volume would rise suddenly, as if a volume pedal was pressed, and then the volume would drop back down.

It did this without any noise and without loss of clarity.

Thoughts???
 
Robert Herndon said:
Spent a few hours playing this last night - at volume levels a title less than 1/2 - and it acted strangely again but then cleared up and worked fine.

While playing, the volume would rise suddenly, as if a volume pedal was pressed, and then the volume would drop back down.

It did this without any noise and without loss of clarity.

Thoughts???
Click to expand...
Possibly a pre amp tube, but that would be hard to diagnose, if it’s just a fluctuating occurrence
 
Robert Herndon said:
Not a big deal, but I figured I would post the question here and at the Marshall Forum.
Click to expand...
The MF is going to tell you more than you are going to want to hear,
Myself I would drop 4 new preamp tubes in it with out batting an eye, and test again!
The way you have just tested it, another thing to try is with it up and running, take a pencil and tap the power tubes, if you see anything out of the ordinary, replace and rebias the amp, they are a bit finicky with tubes
 
My others have been no problem, but one of my white ones that has had no issues is making a funny little popping noise sometimes,
so I need to pay attention to my own advice !!
Cheers Mitch
 
Mitch Pearrow SJMP said:
The MF is going to tell you more than you are going to want to hear,
Myself I would drop 4 new preamp tubes in it with out batting an eye, and test again!
The way you have just tested it, another thing to try is with it up and running, take a pencil and tap the power tubes, if you see anything out of the ordinary, replace and rebias the amp, they are a bit finicky with tubes
Click to expand...

I am going to separate the chassis form the cabinet and look for hidden modifications, like the 'C-19' mod, or any damage. Then I will likely swap the tubes too....
 
ran the dsl into this for recordings..the jcm 800 era vintage/gt75(very 65 like) talk about balanced..my studio guy had it on the graph..said it was the most complete frequency coverage in all his years he eve saw..the vintage filled in the middle what the gt75 is missing & its an efficient cab. i call it the hard rock cab..,use the greenbacks for more rock..can push the greenie a lil for some give & personalityx pattern (2).jpg
 
syscokid said:
I hope you check all the tubes. And since your pulling the chassis, start chop-sticking all the components and their connections, cables, ribbons, etc...
Click to expand...

I'm going to look for signs of tampering and modification first.

Since this is happening at fairly low volume, would you rule out power tubes???
 
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