Mark III, possible issue...

[Facelift]

well sort of. I got some NOS preamp tubes in and was testing them out in various slots. Knowing I had to pull the 2 6L6 tubes out of their sockets in order to reach in there to get to the pres out, I did so. Anyway, after changing a preamp tube I turned the amp back around and turned it back on. I normally have the master volume set around 3-4 but this time had it about 2, if that, and was playing through the lead channel. I had noticed it sounded kinda thin so I just thought maybe it was the preamp tube still warming up so I jsut kept playing. My guess would be between 5-10 minutes. The sound wasnt getting any better so I figured maybe the tube I put in was bad. After all, 2 of the NOS tubes i got were highly microphonic. So, I turned the amp to standby, turned the amp around and noticed :shock: "oh crap" I accidentally didnt put the 2 6L6 tubes back in thier sockets. I turned the amp off immediately and put them back in, turned the amp back on and whew, the sound was not thin anymore.

Now, heres where I think I "might" have an issue. Its either one of two things. Like I said I normally have my settings right around here, master volume anywhere between 3-4.

Anyway, the amp seemed like it was a hair quieter than normal in simul-class mode. Since it was on 2, I turned it up to three. It got louder but didnt seem to be as loud as before on 3. So I turned it up to 4. Still same thing, louder but not quite as loud as before. The sound is still huge and there seems to be no noticable loss in tone or balls, just a little volume. Its either that or Im going deaf, but my recent hearing test I took for work work suggest thats not the case.

So my question is, did I possibly mess something up by not having those 2 power tubes in thier sockets and having the amp turned on? I read thats one way to tell if you have a bad power tube is to take it out of it socket and turn the amp on but no length of time is specified in that. It doesnt seem like there is a drastic difference in volume but its enough to make me think I might have a volume loss, or Im just used to it.

Just so its clear, all tubes (pre and power) light up like normal. THere are none of them that are dimmer or brighter than the others.

Any ideas of what could be going on if in case I damaged something?

One other thing. Why does this amp sound better out of the chassis than it does inside the chassis? Only two things I can think of would be becasue there is no fan blowing on the tubes, and the reverb tank is unplugged when out of the chassis.


Thanks for any insight.

 

[MrMarkIII]

"... one way to tell if you have a bad power tube is to take it out of it socket and turn the amp on..."
This works if you replace the suspect tube with one known to be good.
Otherwise, as you have learned, removing tubes and running the amp does not give satisfactory results.
All tubes have different degrees of "brightness" and I wouldn't use that criteria to determine viability.
Mesa's are over-built, so if the amp works, you should be fine.

 

[Facelift]

So I take it the slight volume loss could be just my imagination?

 

[MrMarkIII]

Could be. It's weird how your ear gets used to a sound, then something changes, then OMG, my amp's awful now. All it takes is a bumped knob, a moved slider on the Graphic, or maybe one of those pre-amp tubes you switched.

 

[Facelift]

Hmm, maybe Ill try swapping them around tomorrow again.

As for my other question, any idea why would this head would sound better with the chassis out of hte headshell rather than in? I thought i read that even though the reverb is turned all the way down that its still on and slightly present. Could this be it or could it be from the tubes getting hotter becasue of no fan, or both reasons?

Thanks for the responses so far.

 

[MrMarkIII]

If you use the Reverb/Graphic foot switch, that's the way it works. You can still use the knob to adjust the maximum reverb, but when you foot switch it OFF the reverb goes to a background level. So if you turn the reverb up to 10, the foot switch will turn it down to maybe three. The lower the knob, the lower the background level as well, but it's never totally OFF. That's with the foot switch only.
The Reverb/Graphic foot switch requires a TRS, (or stereo) cable.
As far as the amp sounding better out of the shell, well, you must have better weed than me, dood. :lol: