EVH LBX II potential bad tube?

[Gonzalo]

Hey guys,

I bought a used EVH LBX II on Reverb and having some issues I'm trying to troubleshoot.

Clean channel sounds amazing and takes pedals really good. With the crunch channel is a whole different story.

With volume at 0 when the gain is past 3 o'clock its starts giving me a ton of feedback. Also volume goes from nothing to super loud from gain 0 to 0.1 (I had to lower the volume pot on my guitar to 1 for video).

Furthermore the volume pot seems to have zero effect on volume. Be it at zero or 10 its the same volume, just more hiss the higher I go.

Please see video attached with demo:

Appreciated

 

[Gonzalo]

ok. I opened the caged and made sure that all tubes are properly seated. I checked all tubes with a wood pencil to see if there was any tinging and all seemed good.

I exchanged the V1 and V2 tubes (which according to diagram are the preamps for each channel) between each other as well and the amp started behaving differently.

Clean channel still works well as before.

Crunch channel:
- Initially (prior to video) with the volume at zero I was able to crank it to 7-8 with no issues and volume was fairly low. I would touch the pot a bit (like prick it) and the volume would jump up. Eventually the volume stayed up and I wasnt able to turn it down again.
- Afterwards the volume pot started behaving the same again. No change between zero and 10, but I was able to get the gain up to 7-8 and play for a bit. Within 10 minutes though the feedback started coming back and by the time I filmed the second video I'm having similar issues again (although much less than before).

Any thoughts?

 

[Gonzalo]

ok, seems the V1 tube is bad. Is this the correct assessment? Not sure if it comes out on the video but I do hear a harmonic when tapping it, which I dont hear on the rest.

Video ->

 

[efiltsohg]

Do you have any other tubes you can try? Pull from a different amp maybe

 

[Gonzalo]

I went to guitar center and bought a new tube. Is a bit better, but I dont think that is the culprit here. I think its a bad volumen pot.

Check this out. When at zero I pull on the know a bit and it cuts the volume down to like 10%, when I push it back in a bit it goes back to super loud. Once its super loud, there is no noticeable difference between zero and 10. That cant be right...