Marshall DSL100H grounding issue?

[ntek]

so yesterday for the first time i was experimenting with running 2 amps; '82 JCM800 50watt left side output from my line6 DL4 delay and my DSL100H from the right side output on the DL4 delay so i could experiment with ping pong, stereo delay etc. i'd never had a problem with the DSL100H in the 5 years since i purchased it new, and after about 30 minutes playing it, it started making loud pops and i noticed one of the power tubes flash/spark. Both the heads were plugged into the same wall outlet. I could not get the DSL100H to recreate this issue today when i tested it by itself (no other amp connected). I initially suspected it was a grounding issue, so i checked the 3rd prong on my wall outlet with a multimeter to make sure it was grounded and it is in fact grounded. also both amp chassis are grounded to their 3rd prong. I am NOT using an ABY line selector, though i do own a BOSS AB selector. my question is - is my setup causing some sort of grounding issue between the 2 heads? Or is it more likely a component is starting to fail on the DSL100H? I tend to think it's a problem is using the 2 amps in tandem since the problem does not exist when i use the amp by itself. I kinda want to see if the BOSS A+B selector will alleviate the issue, but at the same time dont want to risk further potential damage to my amp. The DSL100H has very low hours of usage on it, however i have not replaced any tubes on it in the 5-6 years i've owned it (still has factory tubes). Thanks in advance for any suggestions/help.

 

[GregVanz]

so yesterday for the first time i was experimenting with running 2 amps; '82 JCM800 50watt left side output from my line6 DL4 delay and my DSL100H from the right side output on the DL4 delay so i could experiment with ping pong, stereo delay etc. i'd never had a problem with the DSL100H in the 5 years since i purchased it new, and after about 30 minutes playing it, it started making loud pops and i noticed one of the power tubes flash/spark. Both the heads were plugged into the same wall outlet. I could not get the DSL100H to recreate this issue today when i tested it by itself (no other amp connected). I initially suspected it was a grounding issue, so i checked the 3rd prong on my wall outlet with a multimeter to make sure it was grounded and it is in fact grounded. also both amp chassis are grounded to their 3rd prong. I am NOT using an ABY line selector, though i do own a BOSS AB selector. my question is - is my setup causing some sort of grounding issue between the 2 heads? Or is it more likely a component is starting to fail on the DSL100H? I tend to think it's a problem is using the 2 amps in tandem since the problem does not exist when i use the amp by itself. I kinda want to see if the BOSS A+B selector will alleviate the issue, but at the same time dont want to risk further potential damage to my amp. The DSL100H has very low hours of usage on it, however i have not replaced any tubes on it in the 5-6 years i've owned it (still has factory tubes). Thanks in advance for any suggestions/help.

Bad tube, cut and dried

 

[guitarbilly74]

The hum and pops are normal when splitting your signal between 2 amps. It's called a ground loop.

The first thing you need to do is to make sure the all the effects are being powered by a power supplier with isolated out like a Voodoo Labs, CIOKS etc if you're using wal warts or daisy chaining power to your pedals that won't work.

Then you also need to isolate your audio path. The easiest way is to lift the ground of the cable going from your delay to one of the amps. You can do it yourself or buy a "humbuster cable".

Or you can buy an audio isolator like this:

https://www.sweetwater.com/store/detail/CleanBoxII--art-cleanbox-ii-2-channel-hum-eliminator

 

[TheKman76]

An earth loop is very unlikely to cause valves to arc. While you, no doubt, have an earth loop with the setup, if there's no audible noise or hum through the system then there's no pressing need to address it.

Valve arcing is very likely to be a bad valve. It may just be a wonderful coincidence this started at the same time. Five years is a good innings for power valves, time for some new ones.

 

[guitarbilly74]

Tube issue was the first thing that occurred to me too, but then he mentioned that he tried the amp by itself and the problem went away. That's strange, because a bad tube would be an issue even with the amp by itself. So I was thinking the ground loop was introducing some kind of noise or interference that the power section did not like. But I agree that it's not a bad idea to replace tubes on an amp after 5 years anyway. maybe do both (replace the tubes and isolate the ground) and see if that helps.

 

[LyseFar]

I am using a Palmer Line isolator box to avoid ground loops. Cheap and easy solution when dealing with more amps at once.

Palmer RIVER wupper | Line Isolators | Palmer

The more complex the setup, the higher the chance of ground loops. With the Palmer wupper Line Isolation Box, everything is quiet again so you can enjoy your audio without humming and buzzing. The Palmer wupper is an isolation...

www.palmer-germany.com

I have the old version but same same.

 

[ntek]

An earth loop is very unlikely to cause valves to arc. While you, no doubt, have an earth loop with the setup, if there's no audible noise or hum through the system then there's no pressing need to address it.

Valve arcing is very likely to be a bad valve. It may just be a wonderful coincidence this started at the same time. Five years is a good innings for power valves, time for some new ones.

just a follow up to my original post. Looks like Kman78 was correct - it's 100% a bad power tube. i finally got my box of replacement fuses today so i tried popping in an a pair used JJ's that i had from when i replaced my JCM800 power tubes, and THAT seems to have resolved the issue. I was able to play the amp for over an hour without any issues. IDK if its just my ears of the JJ's give it a softer/warmer distortion / overdrive compared to the stock Marshall EL34 tubes.