So I was playing my EVH earlier tonight for a couple hours and I switched from channel 3 to 2 and got no sound. Tried channel 1 right after and I got no sound either. Channel 3 works fine. I was playing both channels 1 and 2 earlier and they were fine. Tried just changing the channels on the amp instead of the foot switch to see if it was the switch but still no sound. I hadn't disconnected the foot switch to test this, not sure if this matters. I turned the amp off right after as I was about done playing for the night anyway so that's as much troubleshooting I have been able to do so far.

On channels 1 and 2 there is still the normal background noise that the amp would produce when I'm not playing but when I play I get nothing at all.

From what I've read on the ol' google, seems like it could be a preamp tube has gone bad but I've never had any problems with a tube amp before so I really have no idea. Have read also that the foot switch cable can be a little shoddy so I suppose it could possibly be that as well.

Anyone have any idea what it could be that's caused channel 1 and 2 to die?
Preamp tube, IIRC channels 1 and 2 have some shared tubes. If you google something like "EVH 5150 III tube layout" (or there may be one in the manual) you can work out which tubes are shared, then swap them out one at a time for a new tube, providing you have spares.


Tube layout for 100W version: http://support.evhgear.com/schematics/EVH_5150III_TubeChart.pdf

50W version: http://support.evhgear.com/schematics/EVH_5150III_50W_Head_Tube_Layout_and_Functions.pdf
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Last edited by GABarrie at Aug 30, 2013,
Buy the looks of it try a new tube in V1,V5 or V6
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Ideally you'd have spares, as mentioned, but if you don't just try moving preamp tubes around. If the problem 'moves' with the tubes (for example after switching them channel 1 and 2 may work but 3 may stop working) then you know it's a bad tube. If the problem is unchanged by moving the tubes then it is something else. Good luck!
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Unless its electronic drums.

I'm trying to switch the V3 and V4 tubes with V5 and V6 but for some reason I'm having a hell of a time getting the things back in.

It looks like the pins are lined up correctly but it doesn't want to move at all, I'm pushing down pretty hard and it just wont budge. Not sure if I'm doing something wrong but it's pretty lame, 3:30am right now and I didn't want to spend all night doing this.


Alright so I tried again and was able to get them back in in like 10 seconds...

As I thought, and the rest of you suggested. It's one of the tubes in either V5 or V6 that is causing the issue. For about 2 minutes all 3 channels actually worked fine and then all of a sudden channel 3 cut out and 1 and 2 were working like wonders.

So my question now is; Should I replace all 6 preamp tubes or just V5 and V6? Supposedly, the amp is only around 4 months old but after receiving the amp and finding out the amp wasn't in the condition it was claimed to be I'm not sure if that is true.

Also, from what I've read the newer EVHs came stock with JJ tubes but all 4 preamp tubes I took the covers off of were unlabeled. Is this normal? I really liked the tone I was getting so I would like to stick with what was in there to start with if possible.

And thanks to the three of you who responded already, you were all very helpful.
Last edited by supergohan931 at Aug 31, 2013,
Check that you haven't bent some pins on the tube. If you have, straighten them with some needlenose pliers.
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I was very careful not to wiggle them around so I didn't bend them, was afraid they were going to break off or something

I edited my last post as I ended up being able to get them in after a second try without any issue.
Just replace those 2, or even one (you can work out which one is dodgy by swapping just one of them back).

JJs I would say will only improve the sound you're getting, they come with plenty of balls and enough clarity. But if you replaced a couple you'd get an idea what they would do to your sound.
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50 watt head comes stock with JJs, website and manual says so, though I never checked to check how legit it was on my amp. If you have the 100 watt head, then I don't think they specify what comes stock in them. Should be fine to buy one new valve, try it in V5 and if that doesn't work then put it in V6. Though you should probably buy 2 to have a spare one incase it happens again.
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