Bad tube? DSL100H

[TysonMRox]

Hey dudes, I’ve never posted here and don’t know what I’m doing. Anyway, about a month ago my amp started making popcorn noises and a loud, low hum. Sometimes switching it off and on would help, sometimes it wouldn’t. I’ve had it for 5 years and it’s been gigged and played hard for most of that so I would assume it’s more than time for a tube to go bad, I just don’t know what a bad tube sounds like. Thanks guys.

 

[Shawn Kawvey]

..

 

[TysonMRox]

Thanks man. I want to take it to a tech but I don't know any around here. Anyone know any good techs near southeastern Ohio?
I tapped on the tubes and one of them made noise, but then I swapped some around and found that any tube in V1 makes noise, but only sometimes. And tapping on the second tube would sometimes make the loud humming start, then I'd hit the top of my amp like the Fonz and the humming would stop. I'm now even less sure what's wrong than when I started.

 

[Chris-in-LA]

5 years on a set of tubes is a lot. Try getting a few new preamp tubes and do a few substitutions. Most Marshalls run 12ax7’s in the preamp, not sure about your specific amp. And, more than likely your power tubes also need replacing if you’ve worn out your preamp tubes. Do you know how to bias your amp?

 

[TysonMRox]

Yeah, they’re 12ax7s. And not really. I’d just throw more EL34s in it anyway. If they survived this long, would the factory bias be fine?

 

[Matt_Krush]

. If they survived this long, would the factory bias be fine?

Yes, No, Maybe.
Why?
Tube variance by manufacture..and even within a manufacturer, is not a tight tolerance. Internal resistance/mu can be all over...thus current draw from the tubes can have a significant swing from low to high.
And one manufacturers rating system means NOTHING compared to another.

So, could be any one of the answers...only way to know if the bias setting now will work with new tubes, is to actual check the bias...
There are a million videos you can watch, even if its just to know how to do it...its worth knowing.

You can just toss in EL34s to a quick function test, but if a tube starts getting hot/red-plating...shut the amp down quick....oh, make sure you get a matched quad set.

Safest bet however, is to check/adjust bias whenever installing new output tubes.

 

[Lance Chambers]

I think you have a grounding issue.

 

[TysonMRox]

Does this help?

 

[Yamariv]

Does this help?

I've heard alot of bad preamp tubes while amassing my vintage tube stash but that's an odd sound I've never heard before. I'd guess its the power tubes, buy a matched set, bias them and see if that helps. 5 years is alot on a set of modern power tubes so if it's another problem you're not really out cause you probably should change them anyway if they have a lot of play time on them.

General rule if you don't have all the gear to work on amps (knowledge, variac, dim bulb, tube tester etc..) that if your amp suddenly starts acting weird out of the blue, it's probably a tube. Of course it could be something else yes, but generally weird intermittent sudden problems would point you to a tube.

 

[TysonMRox]

So, who votes take it to a tech vs get some pre and power tubes and wing it with the current bias? Side note, I’ve seen some posts that say the factory bias is 90mV, and then people saying that’s really high for other Marshalls. Anyone know a good voltage for a DSL100H?

 

[TysonMRox]

For all with a similar problem who come across this in the future, tubes were bad (didn’t see that coming), and there were also some cold solder joints on two of the tube sockets and a wire coming loose somewhere.
Re-tubed with JJ E34L’s and ECC803s. Sounds rad.

 

[Dogs of Doom]

So, who votes take it to a tech vs get some pre and power tubes and wing it with the current bias? Side note, I’ve seen some posts that say the factory bias is 90mV, and then people saying that’s really high for other Marshalls. Anyone know a good voltage for a DSL100H?

72-79mV per side...

 

[Dogs of Doom]

are you using the 16ohm output?

I say, if you aren't experienced in fixing electronics, especially tube amp's, you might want to take it in this time.

1 thing you can try 1st off, is spraying some de-oxit on a guitar cable, & insert it into the input jack. Insert it, then spin it around, then act like you're having cable sex w/ the input & plug in/out a few x's.

Do that w/ all the jacks on the amp. Use the speaker cables to do the speaker jacks, on both amp & cab. Do it to the effects loops as well.

I just had a non master volume, 2 channel amp, that I jumpered the channels w/ a dirty cable, that hadn't been used in years (oxidized plugs) & it made similar awful noises...

If you just decide to take it in, have the tech go through & give it a thorough cleaning & lube & to check for cold solder joints. Tell him that you might need to hardwire the ground on the 16 ohm output jack, so that it's always connected to the 4/8 ohm, because the inside connection/switch goes bad & will cause grounding problems when using the 4/8 ohm jacks. (very bad, if this happens)