symptoms of cap death?

[guitardude05]

so i turn on the ole' mark iv today and use tweed power like i normally do when im just practicing alone. i started jammin on the lead channel and i notice the volume was kind of low for the settings i had. i messed around with the master volume and channel volume and the amp is just not getting as loud as i want it to.

hmmm.. so i go to R1. almost NO volume. i turn the channel volume to 10 and its not close to the volume i usually get.

okay, so i changed some tubes and it didnt really improve the problem. i switch to full power and its still not giving everything it seemed. whatever. i leave for a while, come back and the amp seems to work better now.

could this be maybe just my ears playing on me or is this a sign of possible cap death? the amp is from 97 or 98. the last time i had the chassis out (about in February) everything looked fine to my eyes. no buldging caps or anything like that. ive probly put about 100 hours on the amp since then. i will have to take it out again and check but i cant imagine them going bad so soon. anyone have any advice?

 

[Harry the Horder]

A sure sign of cap death is a change in tone and also extreme death or total failure would bring on motorboating as the cap would no longer filter out the cycle noise when the ac gets altered to dc.
When mine where dying I noticed that when I played the bottom strings-low E I got a bit of distortion as if my speaker was slightly on it's way out and sure enough one of my caps had the tell tell bubble.

 

[Monsta-Tone]

It's a good idea to change them out eventually anyway.

I would check a few things 1st though, maybe you already did some of these.


Change out the PI tube, I think it's V5 on the Mark IV.
Try new power tubes.
Also, maybe see if you bumped the Triode/Pentode or Class A/Simul switches. The Class A may just give you this type of result.
Check the speaker connections, or better yet, try the amp with another speaker.


If none of these work, and there are sure to be more, but it's not even 6 am yet, then maybe it's time for new caps.

 

[phyrexia]

maybe you didn't let the amp get hot enough?

 

[guitardude05]

i dont know what was going on, everything works fine now but the channel volume is not as sharp from 0-2. it is a much more gradual volume change now... im probably just going deaf cause i notice i have to crank my stereo louder than ever to play along with the amp.

 

[mr_fender]

Dirty pots maybe? Could possibly account for the change in the pot behavior if there is/was crap on the wiper of the master pot(s). Dust and smoke can find its way into the craziest places. If any of the pots are scratchy, contact cleaner couldn't hurt.

Also, don't rule out bad cables. A bad connection on a patch cable on my pedalboard had me chasing my tail changing tubes once. Intermittent problems can be a real pain to track down.

 

[guitardude05]

okay, the volume just kept getting worse and worse and i knew that something was terribly wrong with this. i took out the chassis and everything was visually fine, the orange caps all had a small bulge on top, but i assume that is probably a manufacturing thing. thats the only that caught my eye.

i had bought 3 mesa boogie 12ax7's at guitar center about 2 months ago. when i put them in 2 months ago, there was no volume change, but the tone was great. there was lots of gain and it was really crunchy. so 1 by 1 i took them out. v2 first, replaced with a sovtek. there now my volume is back. v1 didnt make too much difference, but i change v3 and now there is bass that i never remember having. but there is not as much gain it seems anymore.

the 3 mesa 12ax7's are black labeled, but i have 2 old ones that are white labeled and they work great. i am so sick of tubes... but why would these 3 slowly die??? hopefully v2 doesnt go out again, then i will know its more than just a tube issue. :?

 

[kiff]

your symptoms remind me somewhat of what I've had. our problems aren't indentical, but some (low volume from v2) seem to be overlapping. I plan on taking mine to a local tech soon, but after my band has some time off. let me know if you solve the problem and i'll do the same...

http://forum.grailtone.com/viewtopic.php?t=27955

 

[guitardude05]

im not sure what to think. i had a tung-sol in v1 about 6 months ago and it was done within about a month. and at least 2 if not all 3 of these mesa tubes i had been using are done. maybe i am just unlucky with my tube purchases (which i hope) or maybe something is wrong internally causing premature tube failure.

i was just jamming out for about an hour because with these new tubes in i am really loving my tone. there is a tad less gain, but i think it is for the better. it is mean as hell and my pinch harmonics are really coming through now. hopefully my preamp tubes will hold up for longer than 2 months...


oh and 1 more problem......... when i switch to r1, there is about a x2 increase in volume of r1 right when i switch for a split second. like if i am playing and dont stop to switch channels it gets super loud for a millisecond before resuming normal volume. whats the deal!?

 

[Monsta-Tone]

The orange caps are your tone caps and coupling caps. They are not electrolytic and it is very rare that one would fail. The orange hump on them is due to the manufacturing processes. It looks like that is where the machine holds it until the leads are applied and it is dipped in the orange plastic. Don't worry about these.

The Electrolytic caps are long, cylindrical things. They should be some of the largest components in your amp, other than the transformers and tubes.



Look at your manual and it will tell you which tubes have which functions.

As for the new tubes, sometimes they are damaged in shipping. I also have heard from a few people that the TS tubes may not be all that sturdy. I have one in V1 of my DC-5, but I got it from Doug's Tubes. He tests them all before selling them so that he can weed out bad ones.

All tube brands have failures right out of the box. The Mesa ones are tested, but anything can happen to a tube after or during shipping.

If you're tired of tube issues and they pop up again, spend the extra money and call Eurotubes or Doug's Tubes or KCA NOS Tubes. You won't be disappointed.

 

[kiff]

does anyone have a link to a tutorial for replacing caps? discharging the caps, tear-down sequence (mark4), replacement cap values (and vendors) and anything else that applies...

 

[Monsta-Tone]

Safety Tips: http://www.aikenamps.com/SafetyTips.html

Glossary of Terms: http://www.aikenamps.com/AmpTerms.html

Capacitor Information: http://www.aikenamps.com/CapConvert.htm

The guys here are incredibly helpful: http://www.fenderforum.com/forum.html?db=&message_area_number=22&lastpost=2008-08-3021:24:00

Great Information Forum: http://www.el34world.com/Forum/index.php?board=13.0



You could also do a search here on this forum. There must be 100 threads on how to replace caps.

 

[kiff]

Cool, thanks for the links!

You could also do a search here on this forum. There must be 100 threads on how to replace caps.

I actually read many, but the ones I read didn't go into any details...