Smoke from F-50 combo

[mikeyp]

So I was doing a little playing this morning while nobody was home. Had it cranked pretty good on channel two when it went to less than 1/2 volume. I jumped off the couch and put it on standby, tilted the amp forward so I could peak at the tubes and through the vented panel I saw a puff of smoke coming from above one of the power tubes. I about **** myself and turned the amp off completely. At this point I had about 15 minutes before I had to leave for work.

So while writing this I got a callback from Mesa. They said even though there was smoke, it may not be that bad and could just need new power tubes. :? They are about 3.5 years old so that probably isnt a bad idea. Would any of you just stick a set of tubes in and turn it on? It would seem to me that it should atleast be inspected to see what was burning. What sucks is the authorized repair shop in this area I'm familiar with. It is extremely messy and they could'nt fix an amp I took to them, though they said it was. This blows.

 

[MusicManJP6]

Not sure about the smoke, but it could very well be as simple as replacing the tubes. Did you happen to notice if one power tube was lit and the other was not when you tilted it forward? I'd try replacing your power tubes and testing before taking it to a tech if it was me. Let us know what you find out.

 

[Old BF Shred]

Did it blow a fuse? And are you sure the fuse in it is the right size? Don't laugh, there are posts here about this. If you are the original owner then you should know if it is OK, but....... :roll:

If a tube shorts internally, it will usually blow the fuse.
Also it could partially fry the screen resistor causing smoke (this does not always destroy the resistor, but usually does. Good thing it's a fairly cheap repair).

Did you notice an orange-ish glow from the tube(s) when you looked at it?
You can try new tubes (Mesa's or bias range specifically for Mesa amps)...unlikely to do any additional damage at this point (assuming it was caused by the old tubes), but I'd watch it closely for a while....

But, smoke is generally not a good sign...something just plain got too hot in order for this to occur.
And generally, if just one output tube goes (out of two), it will still be significantly louder than 1/2 volume. Could be another issue.

Probably should have a tech check it out so you know for sure...sorry to hear there is not a good one in your area.
Good luck!

 

[mikeyp]

It all happened pretty fast but I think both tubes were glowing. Not sure what color. I did pop out the fuse on the back and it looked ok. I can take a better look at it later. I am the original owner so unless a fuse gremlin came by the house one night it should be the right one . Yeah the smell from electrical smoke cant be good. There is another tech about an hour away that I may have to try. Being it is still under warranty I dont want to see it get fixed with jumper wire, know what I'm sayin'. I would almost rather send it to Mesa because I'd hope they would "make it right". Thanks.

 

[mikeyp]

I tried a set of JJ's I had laying around. They have low hours on them and I figured even if they aren't correct bias wise at least I'd get an idea. Amp turned with no smoke. Clean volume seems a bit low and it breaks up way early. It's harder to tell on the dirty channel but I'm pretty sure its a little muddier than it should be. Could be the JJ's there. I guess it's probably time to take it to a tech. I wonder how upset they'll be if I bring my own new tube's?

 

[mikeyp]

Being me, I decided the least I could do is take the 4 screws out and have a look around inside. What I found was this

I soldered it back in place, although from the top, and the amp seems to be fine. Would you think those two resisters should be replaced anyway? Anyone know if they are directional?

 

[Old BF Shred]

They are not directional. Looks like the screen resistors......This is a common problem with the early run Stiletto Ace combos...the heat from the tubes melts the screen resistor's solder.
Looks like you found it. You may want to be sure the leads are a tight fit....that is, it should hold on to the connection points without any solder on it, or it may happen again.
And CAUTION! there may still be high voltages from the power supply capacitors...don't get zapped! 8)

Also, BTW, be careful taking in a Mesa amp for warranty with non Mesa tubes ...they say it voids the warranty.

Good luck

 

[mikeyp]

I guess the bad tube caused it. I wondered if it was a good thing it fell out. Would other damage have happened it it hadn't? Almost like a they put them in upside down for that reason? I did call mesa and they suggested I take it to get checked out even though it seems fine. It is under warranty. It did have the original tubes when this happened, which is probably why it happened. I told them I only put the JJ's in for testing purposes. I was starting to think about new tubes but just hadn't done it yet :roll: . Mexican reristers huh?

 

[Old BF Shred]

Mexican reristers huh?

Perhaps Chinese.....
The fact that they fell out of the solder points without "looking" like they were totally fried indicates the solder melted and they fell out. Looking at the photo, you see the other resistor is connected with the leads coming up from under the PWB (circuit board). If hot enough, good 'ol gravity allows them to drop out. This is what the Ace combo is famous for. The head version(s) don't have this issue as the tubes are above the chassis (not below) and the heat rises up away from the PWB, not into it.
Having said this, I would still have them check it out, as it is under warranty, and there could more to it than a description or photos can reveal.
If you have the old tubes, I'd put them back in, but let them know you suspect one may be bad (whether it is or not) so they don't just fire it up with it in and cause more damage (although it may not be bad after all, why take a chance?) As far as how other brand tubes will affect your warranty, that basically boils down to Mesa's call on a per-case basis. Since it happened with the stock tubes, just be sure they understand that and I'd like to think they will be reasonable about it.

Either way, good luck!

 

[UKBoogieboy]

My F50 used to keep going to half volume and losing everything. Needed a new set of valves every gig. The shop has now giving my a credit note for the full amount. They sound good when they are working but you can't rely on an F50, two have played up that I used.

 

[mikeyp]

Well this problem was due to a power tube going bad. My f-50 was trouble free before this and so far it has been since. Hope I don't get your luck. :wink: