Tube Amp Problem [SOLVED]

[zayance]

Ok plugged sine wav in Return Loop, i have Signal in Grid 2 Of V3, nothing on Grid 1 of V3

PS, i've edited last post on page 2.

 

[mad.ax]

Ok plugged sine wav in Return Loop, i have Signal in Grid 2 Of V3, nothing on Grid 1 of V3

With or without V3 pluged?

Axel

 

[zayance]

Without V3 Plugged

 

[mad.ax]

Ah ok. But something sounds wrong. When you inject signal in the return jack (= V3b grid) you can hear it (assuming that V3 and the EL84s are plugged), then if you traced the signal trough V1 & V2 till V3b grid, you should be able to hear it too...

Plug everything in and check back...

(I hope this is not some intermittent failure :'()

Axel

 

[zayance]

I hope this is not some intermittent failure

It is , now it works  ??? ??? ??? ??? ??? :'( :'( :'( :'(.

So wierd, i mean i even tested with guitar plugged in before doing back all the test, when i took his amp to my lab etc...., hope it will stay as is, maybe some kind of contact on the pins and the socket of one of them  ??? ???

Anyway, i love electronics, but that's one of the part i don't like, BUT all your help mad.ax, and i really like to thanks you for all this step by step procedure you gave me, i still need to know more about tube amps tough, and this gave me a little apercu of what it is, and i'm sure this simple procedure will help some other folks out there, so Thanks a lot for your patience and time, i really cross fingers that this amp stay as is, becaue intermittent failure, could really be a PITA, when moving amp form gig to gig or so.....

 

[mad.ax]

Intermittent failures ARE a MAJOR pita! Especially if this amp is meant to move from gig to gig...

As a tech, your job is not to cross fingers, but to make sure that this won't happen again

Given the fact that it is intermittent, and how this all started (difficultly swapping tubes in a cheap PCB), I'd say that there's indeed 90% chances that the problem is a mechanically broken pcb trace near a tube socket...

I know you wished you could avoid that, but the only way to be 'sure' is to get your hands on the other side of that PCB...

Cheer up! Can't be that hard... and it's certainly easier than to see this amp coming back on your bench next week!

Axel

 

[zayance]

No it won't be that hard to check underneath, i'll do it, and yes i don't want to see it back on my bench  , so lets get down to work.
So if i don't see some broken PCB trace, i could still redo all the socket solder joints, so to make sure.

 

[mad.ax]

The other 10% chances are oxidized contacts of some sort, either in the tubes sockets, or the NC contacts in the loop jacks...
This amp looks brand new, so it's very unlikely, but you may as well check that too...

Axel

 

[zayance]

BTW, when amp was on, i just slightly tapped the V1 Tube and it crackeled, don't have to right???, all the others didn't.
I just tapped with finger on the tip of the tube, i mean the glass tip of the tube...

 

[mad.ax]

All tubes are microphonic to some extent, especially new 12AX7s! V1 is the place where you have the most gain. So I'd rather worry about a tube that would NOT crackle if I tap it...

Axel

 

[zayance]

Allright, thanks a lot for all these helpful informations, i'll pay you a beer, if you come near the Lac Leman 

 

[mad.ax]

Thanks for the offer...
Of course, if you ever come around Beziers, don't forget to shoot me an email... thought the local beer tend to be red and grape based around here!

Axel

 

[zayance]

, c'est noté.

 

[zayance]

Just another noob question mad.ax, i'm watching at the back of the PCB, solder seems fine, but i'll redo, but the ceramic socket of V1 and V2 are a little loose around the pins if you understand what i mean? Could it be a problem?? Or this is what happens to sockets when pulling in and out the tubes??? Thanks lot.

 

[isophase]

well done guys,
i've learned quite some stuff from reading this post, and even if the problem is not yet 100% solved, i'm sure you will get it right very soon, i hate when things like that happen, personally and until now most of the weird problems i've experienced with tube amps originated from bad tubes (will never buy EH tube again NEVER).
hey, and if you guys ever come to Paris, make a sine
cheers
     

 

[zayance]

well done guys,

All the compliments goes to mad.ax

 

[zayance]

Ok job done, amp working, resoldered, remounted, devil is back again  ;D ;D, Thanks a lot for your help mad.ax.

PS: i've also pinched together the socket pins together just to make sure the pins are in good contact.

 

[mad.ax]

Sorry for answering this late, but I was out for the day...

Just another noob question mad.ax, i'm watching at the back of the PCB, solder seems fine, ...

Maybe I'm just paranoid, but I always feel more confident when I find an obvious fault to fix...

but the ceramic socket of V1 and V2 are a little loose around the pins if you understand what i mean? Could it be a problem?? Or this is what happens to sockets when pulling in and out the tubes??? Thanks lot.

Yes this is what happens to sockets when pulling the tubes in and out... But you did the right thing (pinching the pins...)

Hopefully, your problem was a cold solder joint that gave up... You should molest that amp a bit... Wiggle the tubes, a few slaps on the cabinet... The idea is to inflict shocks and vibrations to see if the issues comes back or not... If the gremlins doesn't start to shout louder than the devil, then you're good 

No needs for compliments guys. I'm just trying to help and share... That's the spirit of this forum 

Axel

 

[zayance]

Maybe I'm just paranoid, but I always feel more confident when I find an obvious fault to fix...

I hoped it was one, but like Pucho stated before

just because a solder joint looks healthy does not mean it is healthy....

So i guess he was right.

Hopefully, your problem was a cold solder joint that gave up... You should molest that amp a bit... Wiggle the tubes, a few slaps on the cabinet... The idea is to inflict shocks and vibrations to see if the issues comes back or not... If the gremlins doesn't start to shout louder than the devil, then you're good  

That's what i did, nothing changed, everything seemed to be fine, i'll do it again tomorrow, before giving back the amp, or maybe will give a little water after midnight  8)