Access to tubes in Combo/Fuzz/channel master observation.

[thalweg]

Hi Everyone.

I tried searching for a tube replacement procedure but haven't found anything detailed.

Access to tubes:
I'm attempting to access the pre-amp tubes in my combo. Does anyone have a procedure to do this? Do I just stick my hand in there and try to get them out? It seems awkward with the power tubes in my way? Do I remove the power tubes first? If I remove the power tubes how would I do a tap test on the pre-amp tubes? Remove that silver bar across the back of the chassis as well?

Fuzz and Buzz in channel 2 Crunch setting:
The reason I'm asking is I seem to sense a little high end static on the channel 2 crunch setting with low gain. It only occurs while playing...it has a buzzy and fuzzy static sound that seems distinct from the core tone. I just want a quick look at the channel two tubes and test if I need a replacement.

Channel Master volume:
While having the master volume in each of the channels at 0 and slowly turning it up I get zero volume increase then a sharp initial transient increase at about the 7-8 oclock position. In otherwords its not a smooth volume envelope but a abrupt one. After that, moving up to higher volumes its fine.


Sorry for all the questions...I'm still in my discovery/honey moon phase of tube amps. I want to explore everything about this amp. Cheers

 

[Rkorn]

Remove power tubes first. When putting the back you should put them on the same socket as before.
One of pre tubes is in an almost impossible place to reach. You will eventually reach it, but putting the cap back on is REALLY REALLY hard...

 

[thalweg]

Thanks RKON...how do you do a pre-tube test with the power tubes removed? I can hardly reach in there now

 

[MrMarkIII]

Is the speaker front or rear mounted?
Look inside the combo at the edge of the speaker frame where the mounting screws are. Is the full frame visible, or does it look like the speaker is loaded in from the front of the piece of wood to which it's attached?
It looks like you can remove four screws and then the speaker grill pops off.
This would lead me to think the speaker is mounted from the front, but you never know.

 

[SteveO]

You could probably remove the grill and pop the speaker out. This would give you all kinds of room.

 

[thalweg]

It appears as a rear mounted speaker. Tho I haven't tried yet. I will do it and report back for the benefit of others thinking about the same thing.

 

[MrMarkIII]

Yup, it looks rear-mounted. Too bad. The idea was to remove the speaker, and then you have that big hole to access the tubes. Looks like a chassis removal instead.

 

[Rkorn]

The pre tube tap test...
do it with the power tubes in!!! WIth a long pencil or something like that... I wasn't able to do it in my MV head... they all seemed ok, but then the guys at the distributor changed them at everything was fine (for a couple of weeks...)

 

[SteveO]

It appears as a rear mounted speaker. Tho I haven't tried yet. I will do it and report back for the benefit of others thinking about the same thing.

I wasn't sure on that, as I have the head version. With it, all I have to do is pull the reverb tank and reach in through the hole in the bottom.

 

[phyrexia]

after two years, i think it is easier to pull power tubes and finagle your hand in there than it is to pull the chassis and return it to its proper place.

of course, your mileage may vary. it is quite a heavy chassis even for me. (i am relatively large.)

yes, even for v1.

 

[Rkorn]

v1 is easy to access with smaller hands... guys with big hands i don't know how they do it. I took half an hour to put the cap back on...
Are the pre tubes caps really that helpful? I believe some older Mesas don't have it. They just have a rubber band with Boogie logo on the tubes. I believe...

 

[golfnguitarz]

I have been wondering the same thing. That sleeve on V1 is an absolute b!tch to get back on. I thought I had it figured out after making a couple of swaps, then I managed to break two preamp tubes putting that stupid thing back on and just called it quits on messing with V1.

 

[>Photi G<]

I have been wondering the same thing. That sleeve on V1 is an absolute b!tch to get back on. I thought I had it figured out after making a couple of swaps, then I managed to break two preamp tubes putting that stupid thing back on and just called it quits on messing with V1.

Mesa has gone back and forth on the preamp tube shields for a while. Early amps, like the Mark I's and II's had them on each tube. They said that the shields blocked interference, since these amps had more gain than the tubes could handle. Starting with the IIC's, shields were only installed on V1, and occasionally, V5. Mesa discovered that only these positions were susceptible to outside interference, and the other tubes became microphonic with the covers on. Around 2005, or so, when the Belton Wave-Solder sockets came about, every tube had its own shield again, because the sockets were recessed in the chassis, so if you bumped the tube, it would likely break on the hard metal chassis. So, the covers went on to protect the tubes from knocks and dings. Also, the amps got even MORE gain, so additional interference protection was needed.