Immensely Irritating 6505 Issue

[StupidDav]

Apologies for the illiteration

Anyway, whilst practicing this evening, my old problem with my 6505 came back after about 3 months of calm to bite me on the ass. Basically I'm playing normally, and then the bass and mids cut out and I'm left with a scratchy mess of a guitar tone. Turned the amp onto standby and theres a 'whoosh' sound then silence, then I turn the thing off standby after about 10 seconds and its back to normal.

I did notice whilst the amp was on standby that the two inner power tubes were noticeably brighter than the outer ones, and I don't believe that they were a couple of days ago, which leads me to believe that this may be an issue with the bias circuit of the amp.

Sooooooo.............anybody got any ideas?

 

[drenzium]

Amp tech, now. You could be doing irreversible damage to your head and/or tubes.

 

[Opeth666]

+1 of what drenzium said

 

[The Atomic Ass]

+2.

Something serious afoot, seek professional assistance, that is, if you like having a working amp.

 

[aeronaut]

I agree with the statements posted above no doubt. Get your amp head to a licensed professional immediately to avoid further damage!!!!

 

[SuperD]

Don't panic yet! Clean the FX loop jacks with contact cleaner ( eg. deoxit). Spray it in the jacks and insert/remove a cord to dislodge dirt and or corrosion. The symptons you describe, while certainly possibly caused by tube/bias issues, are also much more commonly caused by dirty/corroded FX loop jacks, in particular the return jack.
While I would never tell you to NOT get it serviced, based on your post I'm inclined to believe it's the jacks. Fuck the shit outta them with cleaner on a cable, and if they are the culprits the permanent repair is to have your tech replace the jacks...cheap. Hope this is all it is!!! And let us know!!!

 

[StupidDav]

Thanks for all the quick replies!

Amp tech, now. You could be doing irreversible damage to your head and/or tubes.

Just after I got the amp it was doing it nearly every time I used it after about half an hour or so, so I sent it back under warranty, so I'm guessing that if the thing was going to be damaged it would've happened then.

Don't panic yet! Clean the FX loop jacks with contact cleaner ( eg. deoxit). Spray it in the jacks and insert/remove a cord to dislodge dirt and or corrosion. The symptons you describe, while certainly possibly caused by tube/bias issues, are also much more commonly caused by dirty/corroded FX loop jacks, in particular the return jack.
While I would never tell you to NOT get it serviced, based on your post I'm inclined to believe it's the jacks. Fuck the shit outta them with cleaner on a cable, and if they are the culprits the permanent repair is to have your tech replace the jacks...cheap. Hope this is all it is!!! And let us know!!!

I'll get some cleaner at some point in the week and fuck them jacks The last time the problem happened I opened up the amp and cleaned everything out with it, then not a peep until yesterday. Anyway cheers for the replies guys!

 

[The Atomic Ass]

Don't panic yet! Clean the FX loop jacks with contact cleaner ( eg. deoxit). Spray it in the jacks and insert/remove a cord to dislodge dirt and or corrosion. The symptons you describe, while certainly possibly caused by tube/bias issues, are also much more commonly caused by dirty/corroded FX loop jacks, in particular the return jack.
While I would never tell you to NOT get it serviced, based on your post I'm inclined to believe it's the jacks. Fuck the shit outta them with cleaner on a cable, and if they are the culprits the permanent repair is to have your tech replace the jacks...cheap. Hope this is all it is!!! And let us know!!!

If it were just a sound issue, we would all recommend this as a starting point. However the OP stated that two of the power tubes are glowing brighter than the others. That warrants attention by amp techs.

 

[Leuchty]

I hate to bother Joe (lordovchaos) but maybe you should PM him. He may have some kind of idea.

 

[StupidDav]

Yeh I think I may just do that. At the moment I'm thinking (maybe optimistically) that the inside pair of tubes glowing brighter is a problem by itself and the dirty jacks thing reared its head coincidentally But the more I think about it, the less possible that theory sounds

Just an afterthought - its not the plate glowing brighter, as far as I can see the plates are bluish on all four tubes. I think its the filaments.

Pics

 

[AeonSolus]

correct me if i'm wrong, but, doesn't blue light in tubes means bad tubes?

 

[newamerikangospel]

There are alot of things that can cause tubes not to glow the same as each other. Are they matched tubes? Are they matched pairs or quads? The inside tubes may not be matched with the outside tubes. However, one of the best quotes I have seen was something along the lines of "tubes are not light bulbs, so dont judge by their glow".

correct me if i'm wrong, but, doesn't blue light in tubes means bad tubes?

From what I have read when I was asking this question, its just excess mercury in the "vacuum" of the tube. Blue, and blue-green are pretty normal.

 

[StupidDav]

There are alot of things that can cause tubes not to glow the same as each other. Are they matched tubes? Are they matched pairs or quads? The inside tubes may not be matched with the outside tubes. However, one of the best quotes I have seen was something along the lines of "tubes are not light bulbs, so dont judge by their glow".

Well the tubes are the stock Rubys that came with the amp so I'm guessing they are a matched quad Well I'll get some cleaner and clean the jacks and not worry too much about the tubes then. I didn't notice any change in sound at all before or after the scratchy mess tone.
Does anyone know what kind of jacks to replace the send/returns with to stop the shit buildup?

 

[StupidDav]

Bump for progress (or lack of)

I switched the power tubes around yesterday, so now the pair that were in the middle are the outer pair. So now the outer pair glow brighter than the inner, which rules out the sockets I guess. Got me some "Servisol Switch Cleaning Lubricant" and cleaned out the jacks on the back, plugged the thing back in and no dice, still fucks up. So now I got the chassis out and I've just finished cleaning every ribbon cable connector I could get to on the board and gave the return jack another clean. I have noticed theres some discolouration on the transformer bases, and the transformer on the right of the amp if you look at the front, the base is a little bent and discoloured.

The left transformer:

The right transformer:

Don't know if the discolouration on the transformers is important. I'll update if the cleaning didn't work and I'm not really expecting it to.

ALSO I plugged the guitar straight into the fx return of the amp when it was playing up, and there seemed to be no problem with the sound, not tinny or scratchy, it sounded like it should have done, so I'm thinking that the problem is before the power amp. The only thing I can think of is preamp tubes, but when the amp was playing up before I got my single 12ax7 spare and replaced each tube one by one and each time the problem came back. The preamp tubes are 3xJJs 12ax7s and 2x Sovtek 12ax7LPS. My friend's dad who used to make tube amps thought that it was a mismatched cab which was causing the problems, seeing as the cab was a DIY job, but I checked the resistance of the cab with a meter and it came up 8 ohms.

Sorry about the monster post but I'm practically at my wit's end with this thing. I mean they are meant to be practically indestructible and I get the one broken one? Sooooo any ideas? Else this thing is gonna have to go to an amp tech which is a long journey and a lot of money, and I could really do with the cash at the moment.

Anyway /rant and /monster post.