Marshall dsl100H noise question

[Rod]

Hello!


I would like to have sugestions and ideas on what to check where the probem is with all these noise that comes from the amp( see video bellow)?

I allready have done the tapping with the wooden chopstick with a dummy load and oscilloscop and i dont see any problematic areas, any sugestion on what to do next? the amp sounds fine, but the noise as you can see in the video bellow its not fine

https://www.youtube.com/watch?v=Ue3f...ture=emb_title

So i need your tech help here to check were the problem is, and how do i check it and what tools to use to check it?, i know to use a oscilloscope and know electronics.

[The Dude]

Starting at the front end, pull preamp tubes, one at a time, and see if you can narrow down what gain stage is making the noise. It could be as simple as a noisy tube.

[Rod]

Thanks Dude for your reply, But if i pull the v1 preamp tube and leave all the other preamps tubes i will get no sound at all right?

[The Dude]

The point is not whether the amp produces sound. You're just looking for the source of the noise. Or, are you saying the noise is only there when something is plugged in and the amp is operating? In other words, does the amp make noise even with no input and volumes down?

[Rod]

I just checked it out, and the amp makes the same noise without the guitar jack plugged in, so without the guitar cable plugged in im going to pull the preamp tubes one at time to narrow from what gain stage comes the noise, right?

Should i start with the cathode follower preamp tube? If i pull out the v1 tube and leave the others it doesnt mean that the problem is V1 cause the first tube isnt there to amplifi the signal to the other stages rigth?

[Enzo]

Don't over think it. The guitar signal comes in at V1 and progresses through the rest of the tubes. If we pull one of the later tubes and the noise stops, all that tells us is the noise is from before that. Not useless, but not as helpful as the other way. Pull V1, if the noise remains, then it is from after V1. If pulling V1 stops the noise, then the source is in or before V1.

[Rod]

hello again.

Ok i pulled out V1 and the noise stopped so it means that the problem is somehere in the first stage, right?
So now what should i check, what should i look at in the V1 stage that may cause the noise problem?

Thanks for your help.

[Jon Snell]

Firstly, check the valve by replacing it, if still noisy, check the anode load resistors.

[g1]

Do you have another tube to try in that spot?

[Rod]

Yes i replaced the V1 tube with a good know tube for not beeing microphonic, and the noise still hapens, so the noise is not related with the tubes.

[The Dude]

......check the anode load resistors.

^^^^^^That. Also, if you can list the voltages on the V1 tube pins, it might reveal something.

[Rod]

Hello guys.

Again i dont see nothing special in the voltages, in the image bellow you can see the voltages i measure:





I have done some mods to the amp, with trial and error with various componentes soldered in the same spots, so the v1 zone in the board its a little mess :-) ,as you can see in the pictures bellow, could this be the culprit? You can see the little mess i the pictures bellow.
What products can i use to clean the board?
Also some cathode resistors are not easy to desolder at the side of the leg that is soldered to the ground, What is the best way to desolder the cathode bias resistor leg that is solded to the ground? do you have to have a solder iron with more power?

[Helmholtz]

What does CL100mil mean?

[Rod]

I dont know what CL100mil means.

Ok , if some soldered conections werent allrigth, i wouldnt be able to measure the voltage right? So what could be the possible problem generating all that noise?

[g1]

If you have done mods in the V1 area, yes they could be responsible. Post a schematic showing the mods that have been installed.