Help me diagnose a problem

[big bob]

During practice my amp started cuting out. It was like it would lose volume then all the sudden start slowly comming back, then lose volume then faze back.

 

I'm. Guessing rectumfrier tube... ?

[mars_hall]

If it is two output tubes, I would guess one is starting to fail.

[PunkKitty]

To me it sounds like the power tubes are failing. Generally a rectifier will either work or it won't. They don't really fade or cut out.

[Kuz]

To me it sounds like the power tubes are failing. Generally a rectifier will either work or it won't. They don't really fade or cut out.

This is correct, slider (Mike) told me that rectifiers either work or they don't.

[JeffB]

does the amp have an effects loop and do you use it?

[big bob]

does the amp have an effects loop and do you use it?

Yes it has one, no I don't use it.

[PunkKitty]

Put in a fresh set of power tubes. Pre amp tubes, like rectifiers, don't really wear out. They either work or they don't. But if you have multiple pre amp tubes it could be that one of them is failing. But the symptoms indicate failing power tubes.

[JeffB]

Yes it has one, no I don't use it.

sometimes the send/return jacks get dirty/oxidization etc and things similar to what you described happen. It generally just requires cleaning the jacks with doxit*.(*spelling)

I dont know if this is your problem here though.

I used to do a lot of outdoor gigs and would have problems like you describe regularly

Sometimes just turning volume and eq pots full range a few times would help them make contact. Spraying them and the input and speaker jacks with doxit* would often fix the problem. It was seldom tube related but if these general maintenance checks and fix's didnt work, it was a tube thing.

[peterbright]

Invest in some deoxit and use it in the send and return inputs, but it probably is a failing power tube. I try to keep a spare set just to use to check (when I "upgrade" the originals for example, I keep the originals)

[bolero]

what kind of amp is it? and how old?

 

I would guess a power tube as the most likely cuplrit, but there are plenty of other things to go wrong on old amps, if it's the sound city

 

you could temporarily swap in new power tubes & see if it still does it. also watching the tubes as you play could give a clue. there are resistors in there that can go bad due to heat etc & throw things out of whack

 

I assume you have tried different gtr cables, directly into the amp? that will negate anything else in the signal chain. I have heard of bad power in buildings doing stuff like that too

 

ps I would bring it to a tech!

[big bob]

Bolero, it's the carr slant 6 v. I'm not sure what plate voltage it runs at but I'm sure a quick email to Steve Carr would remedy that.

The amp is maybe 13 years old. It has EH tubes in it now, I don't think they are the originals but they have been in for at least the two + years I have had the amp. I know I give them about 10 hours of play time each week including at least one 4 hour stent each week.

 

I have not been able to recreate the weird fluctuations that happened at practice, so it might have been a cable. When it happened I just switched amps as I didn't want to hold up practice, we have a show next week and that was our last rehearsal before.

 

I played for an hour last night, watching the tubes, and while there is no red plating happening there is one that is quite a bit brighter than the others.

 

It was probably something other than the amp, but at this point I'm way too excited about trying new tubes out..... Sooooooooo

There is a new matched quad of jj's on the way, and maybe some new old stock rca's in the near future.

[peterbright]

Can't have too many tubes!

[bolero]

ps I just remembered, I did have an amp that was cutting in & out like that

 

-->turns out the drummer had stuffed a T shirt into the back of the amp to muffle the sound...that was a real bonehead move as there was no airflow & the amp overheated!!

[tbonesullivan]

might just be due for a visit to a tech. I have had cutting out problems with my Mesa DC-5 and my Marshall TSL122. They were completely different issues, and one was peculiar to the amp.

 

I would contact Carr if possible and see what they say. Also giving the whole thing a good contact cleaning couldn't hurt.

[Hfan]

Can't have too many tubes!

+1, all tube amp owners need spare tubes for times like these. Very easy to swap them out one at a time or maybe, with power tubes, all at once and then switch them in and out one at a time to find a possible cause.

[big bob]

Matched quad of JJ's on the way, looking into some NOS as well.

[peterbright]

For reasonably priced good tubes (not the absolute best) go with JJ's.

[big bob]

I'm kinda hoping the JJ's are as punchy as they say. Then I should be able to run them in the fixed bias pair and run some creamy Rca's in the cathode bias set.