• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Mesa 400 help question....

Chef

Chef

In Memoriam
May 23, 2004
41,814
18,945
65
Columbia MO
Disclosures
Staff Reviewer; Bass Gear Magazine
#1
I recenlty bought a used Mesa 400 bass amp. The previous owner had purchased new JJ pre and power tubes from Eurotubes in Feb of this year, had the amp serviced/cleaned/biased-I have the reciepts from Euro and the shop...but, there was a 32 volt 6 amp fuse in the amp; it should have been a 250 volt 6 amp fuse...So, it powered up fine, but as soon as I turned "standby" off, the fuse blew.I replaced it with a proper fuse, and it now powers up and runs/sounds fine, with two caveats I wanted to ask y'all about.
1) Sometimes it "pops/sizzles" just a tad and then quits making that noise. This happens just right after power up, not necessarily after warmed up...I suspect this is likely to be a preamp tube?
2) And, one of the 6L6's rattles a little. I can damp it with just a fingertip on it; and all the 6L6's "glow the same." I've moved it to different sockets, and it seems to be the tube, and not the socket. I doubt the previous owner ever heard the tube rattle in the road case...maybe it had been like that before the fuse blew. It was shipped to me with the tubes removed, I had it out of the rack to re-install them.
I know things like this are hard to diagnose long distance, but I wanted to get your thoughts on things. Mesa service indicated that blowing a fuse that was so dramatically under-rated was a) to be expected, and b) should not have hurt anything.

thanks, alan
 
#2
Can't help you much Chef, good luck though in finding answers. I do notice that mine makes a little sizzle noise too only for less than a second every time I turn off the standby switch and the speaker comes on, don't know enough to know if that is normal or not, but I gigged with it for a good four hours straight Saturday night without a problem, other than the noise when coming out of standby.

Stupid question: Are you letting it warm up for a minute or so before coming out of standby?
 
#3
Chef said:
I recenlty bought a used Mesa 400 bass amp. The previous owner had purchased new JJ pre and power tubes from Eurotubes in Feb of this year, had the amp serviced/cleaned/biased-I have the reciepts from Euro and the shop...but, there was a 32 volt 6 amp fuse in the amp; it should have been a 250 volt 6 amp fuse...So, it powered up fine, but as soon as I turned "standby" off, the fuse blew.I replaced it with a proper fuse, and it now powers up and runs/sounds fine, with two caveats I wanted to ask y'all about.
1) Sometimes it "pops/sizzles" just a tad and then quits making that noise. This happens just right after power up, not necessarily after warmed up...I suspect this is likely to be a preamp tube?
2) And, one of the 6L6's rattles a little. I can damp it with just a fingertip on it; and all the 6L6's "glow the same." I've moved it to different sockets, and it seems to be the tube, and not the socket. I doubt the previous owner ever heard the tube rattle in the road case...maybe it had been like that before the fuse blew. It was shipped to me with the tubes removed, I had it out of the rack to re-install them.
I know things like this are hard to diagnose long distance, but I wanted to get your thoughts on things. Mesa service indicated that blowing a fuse that was so dramatically under-rated was a) to be expected, and b) should not have hurt anything.

thanks, alan
Click to expand...

From a current standpoint, the original fuse was NOT underrated . . . the voltage rating determines what voltage it can break when it blows - not when it blows. IE, a 32 volt fuse may have just arced over in that application, and not protected the amp under a severe failure, whereas the 250V fuse would have done fine. They will both blow at 6 amps, though, so that is not the reason the first fuse let go . . . .

And by rattle on the tube, do you mean mechanically? If so, a lot of times with handling, the cement that attaches the tube to it's base can get loose, doing just that. Just be sure that you don't twist the tube, or the leads to it's base will short, and that WILL blow fused! Myself, if it is really loose, I'd replace it . . . and if thats not what you are talking about, then never mind . . . .

- Tim
 
#5
No sir, the glass seems to be tight to the base...

tadawson said:
And by rattle on the tube, do you mean mechanically? If so, a lot of times with handling, the cement that attaches the tube to it's base can get loose, doing just that. Just be sure that you don't twist the tube, or the leads to it's base will short, and that WILL blow fused! Myself, if it is really loose, I'd replace it . . . and if thats not what you are talking about, then never mind . . . .

- Tim
Click to expand...
 
#6
Hey Chef,

I bought a full JJ tube set for my 400+ and suddenly had the same (start-up)
symptoms as you, plus a tinking sound.

I called Bob at E/T, explained the symptoms. He directed me to pull each
tube and spray its pins with tuner cleaner and work the tube in and out of
its socket a few times.
(problem stopped immediately, and never returned)

I've heard that JJ tubes have slightly undersized pins and can be a more of
a problem (than other brands) in loose/dirty sockets.
(I think I heard, new production JJs have full size pins now)

I also had to bend each half of my bear claw type tube retainers for my
power tubes, because they were barley touching the tube bases.
(I'd check and re-tension yours if needed)

When I first bought my 400+, it was blowing fuses because of a loose power tube.

I'd pull that problem power tube (and the rest) and get out the magnifying glass
and check the pins closely for any signs of arching.
(wouldn't hurt to pull the amps top off, and also inspect your sockets)

I've seen fuses with all kinds of different voltage ratings, but I usually only care about the amp rating.

Are you using slo-blo type fuses?
(my 400+ fuse label, calls for a "8 amp slo-blo fuse")

I've read that Slo-blo type fuse are safe, but a little more forgiving to various situations.

Good luck...:)
 
#7
Hi, Chef

1. Tube amps usually make all sorts of weird noises when turned on/off, AFAIK that's normal, the noises vary with the circuitry, some are generated in caps some in transformers some in tubes. I wouldn't worry.

2. Do You mean that the tube innards are a bit loose, so the mica discs are not touching the bulb and vibration causes them to rattle? That's annoying, but if it doesn't affect the sound, I'd leave it there unless You have a tech who can find a close enough match to the rattling tube. It shouldn't be hard though as the tubes are practically new...so those tubes should be still under warranty?

I've found out that for some reason some of the rattling power tubes perform fine, some don't.

Hope this helps at least a bit.
Sam
 
#8
Anderbass: yessir, slo-blo fuse. Only the one under-rated one let go, I've not had any issues in the 2+ hours of time on the amp since I replaced it.
I can pull the tubes and hit the pins with cleaner, and tighten the retainers.

T-Bird, I dunno why that one tube is making noise. The tubes have a grand total of about three hours on them now, but I'm the second owner of them. Dunno if there's a transferable warranty from Eurotubes, but I have emailed them to get their input. My first post is basically what I sent them this morning...

As I noted up top, the amp-since replacing the fuse-seems to run fine, and sound great.
 
#9
FYI:

Hi Alan:



So the first thing I would do is to clean the sockets which can be done by removing the tubes and then using one of them, spray the pins with some electrical contact cleaner ( you can even get this at a Radio Shack, they call it TV tuner cleaner ) and then work the tube in and out of each socket a few times to remove dirt and corrosion.



Tube rattle is a very common thing if the amp is sitting directly on a cab. It of course doesn’t hurt anything but it’s annoying. The best solution so that more tubes do not start rattling is to place a piece of foam between the head and cab.



Thanks



Bob
 
#10
Chef said:
So the first thing I would do is to clean the sockets which can be done by removing the tubes and then using one of them, spray the pins with some electrical contact cleaner ( you can even get this at a Radio Shack, they call it TV tuner cleaner ) and then work the tube in and out of each socket a few times to remove dirt and corrosion.
Click to expand...

Alan,

Radio Shack sells a much better product for this now: Caig ProGold (now called DeoxIT Gold according to the Caig website, mine says ProGold and is probably NOS). It comes in a "pen" applicator, which is easier to use, and it is also a bit more heat resistant than typical spray cleaners. I've been very impressed with the results it's giving me on repairs and cleaning up ancient NOS tubes so far.

Best of luck.
 

Latest posts

Top Bottom
Back