single rectifier channel 2 problem

[matt_b0527]

hello! this is my first post on this board. i'm glad you guys are all here.

heres my dilemma.

i've got a early 00s 2 channel single rectifier. i was in the studio last week in an iso room with my amp head when i heard a distorted noise coming out of the back of the head. i had just finished tracking the song and the output through the cab sounded fine. anyways, i shut the amp off and finished using a different head.

fast forward a few days and i take the amp with me to work. i take out the preamp tubes to check if they're all good/broken/working/whatever and come to find out that one of them actually had a broken piece inside of the tube (imagine a bad light bulb, how you can hear the filament jangling around, yeah, like that). i replaced that tube (fender gt 12ax7, v2) with a jj 12ax7. i plugged the amp back in, same cables/guitar/knob settings and started playing on the overdrive channel and it just sounded really really bad. i mean awful. it sounded like a cheap peavy. it sounded like there was way too much distortion coming through, like it was overly saturated. instead of being that tight mesa crunch that we all know and love, it sounded like someone was using a buzz saw on top of my amp. i turned it off and replaced all of the preamp tubes with fender gt 12ax7s hoping to resolve the problem...no luck; the buzz saw remains.

the clean channel works/sounds fine. it sounds the exact same as it used to. the gain channel just sounds terrible.

i took the amp to one of the 2 mesa service guys in town and he had it up on his bench for about an hour, looking at the insides of the chassis with me and looking for anything he could identify as being a problem. he said all the tubes were fine. there weren't any visible signs of damage or anything. he is running into an issue of not really being able to diagnose the problem because he doesn't have another single rec to compare it to and to him he just hears the amp as it is now as though its normal. he doesn't have a point of reference, so its really hard for him to try and find out whats wrong. i haven't taken it to the second repair guy in town yet.

based on the information, does anyone have any ideas as to what could cause this problem? i'm really really upset that my amp sounds this way now. i've played this thing every weekend for the last 2 years and loved every second of it. turning it on and hearing it this way makes me sad.

thanks

matt

 

[domct203]

Hello, and Welcome to The Board.

First thing I would do is replace that JJ with another GT 12AX7 and see if the amp's tone returns to how you remember it. Was it a GT 12AX7-C?

Not all 12AX7's sound the same. Even ones of the same brand can have different sonic qualities.

Good luck, and we are here to help if you need it.

Dom

 

[cyber104]

I know this is going to sound crazy/unlikely but have you checked your speaker cable.

I had this exact same problem with my son's Dual Rectifier - drove me crazy replacing tubes

Decided to try another speaker cable and that was all it took

 

[domct203]

Sorry, just re-read your post and I see now that you already replaced the JJ with no luck.

Try replacing the speaker cable as mentioned. You haven't accidentaly used an instument cable there have you?

Dom

 

[Neptical]

Sounds like power tube(s) failure to me, hence the 'buzzsaw'/cheap distortion sound - even though I know you haven't mentioned touching those. But you've mentioned installing all your other 12AX7s back in and the problem remains. So, the way it sounds is as if your getting nothing but all preamp without the power section.

 

[matt_b0527]

thank you guys so much for all of the suggestions!

i have tried a separate speaker cable. separate cabs even, but the problem persists. i've tried about every preamp tube combination i can think of and nothing seems to change it.

i hadn't thought about the power tubes at all. i suppose that could be next on my checklist.

 

[crisis]

I had a bit of a similar problem but one I bought upon myself. I am running a US110v head in Australia on 240v through a step down transformer. One time (actual two) I plugged straight into 240V and blew the fuse. The first time I did this I replaced the fuse and all was good. This time when I replaced the fuse the o/d channel actual lost a heap of grunt. I presumed I had blown a tube and messed around with a few I had but to no avail. I eventually took it to a service guy who couldn’t find a problem. Eventually he called me in to listen and tell him what was wrong. When I got there and listened nothing was wrong, and hasn’t been since. Whatever I did rectified (lol) itself somehow. Anyway I don’t know if that helps you diagnosis, just sayin.