technical help with my 5150mk2

[SimonAdams]

so i bought a 5150mk2 of ebay a couple of weeks ago (i needed the 5150 tone again). and to my dismay i think there is something wrong with it, but i dont know anything about tubes, so i thought id describe the situation to you guys and see if its a tube problem or an amp problem.

the tone is low gain (i had a 5150mk1, so i know what i 'should' be hearing as far as the gain is concerned), even on the lead channel with the gain cranked.

after about 30mins or so of playing the amp suddenly drops in volume and gain.

the first 3 power tubes have a slight blue plasma on the inside, the 4th doesnt. so. i swapped the 3rd and the 4th valves around, so that the 3rd valve was in the 4th socket and vica versa. instead of retaining the blue plasma, the 3rd valve in the 4th socket lost its blue, and the 4th valve in the 3rd socket gained the blue plasma.

the pre amp valves 'do' glow, but VERRYYYYyyyyy slightly. again i dont know if this is normal or not, or how much they should glow or shouldnt.

all of the valves are Sovtek.

if you guys have any tests i can do or anything to determine if its a valve problem then that would be great. its just, im a student, and i dont want to spend £100 on a new set of tubes if i dont need them and instead need to take the amp to a tech...

thanks!

 

[Sweetnothing]

That looks like bad capacitors or semi fried tubes, take it to a tech asap, it's something you should consider amp and guitar wise when shopping on eBay ( I've done it everytime). To my knowledge it looks like one tube is not working well ( could be the tube itself, or the socket in a worse situation) and it's forcing the other tubes to work a lot harder, they glow blueish, mine went blueish when used it at 60W ( two tubes).
Also, when swapping or pulling tubes, remember it's a A/B power section, the tubes work in pairs, and the pairs are 1+4 and 2+3.

 

[Loren Littlejohn]

I just did a re tube on my amp (just the el84s though) and it was only $100 usd installed. It was well worth it. Although my problems didn't sound like yours, I was getting this wierdish orka whale sounds comming from the amp even when no guitar cord was plugged in. Anyhow 3 days and a new set of Ruby power tubes later the amp sounded fantastic.

 

[Mr. Brokenamp]

Ok you said the the 4th tube is not glowing? So take out the 1st tube in relation to that one. You can run the amp like that and see if it will work if that does just go buy a matched quad of tubes and put them in. I know the original 5150 amps are fixed bias so you don't need to go to a tech just pop in the new tubes.