Mark V 25 - Changing Tubes

Hey Guys,

It looks like you have to take the chassis apart on this amp to replace the pre and power tubes?
Can someone walk me through this, or let me know where I can find out how to do this.
Not having much luck finding specific info.

Thanks

Pretty easy. Disconnect the reverb tank, remove the screws in the top, slide the chassis out the back of the cabinet. Reverse to assemble. Power tubes can be changed without removal from the cab, but the preamps are much easier with the chassis removed. Less chance of buggering it up. Keep fingers and tongue out of the exposed electronics.

Excellent, thank you.

I don't need to Bias the replacement tubes do I?

Not on Mesa's as long as you buy Mesa tubes.

barryswanson said:

Not on Mesa's as long as you buy Mesa tubes.

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Can someone tell me what brand of preamp & power tubes Mesa use stock in Mk V 25 ????
thanks :mrgreen:

They are Mesa branded. I don't know who manufactures them currently.

JJ's. There are only 3 companies in the world making tubes, Shuguang (China) New Sensor-[Sovtek, EH, Tung-Sol, Svetlana, Genalex, Mullard] (Russia) and JJ (Czech Republic).

peter_rooter said:

Excellent, thank you.

I don't need to Bias the replacement tubes do I?

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For the power section you will have to get Mesa tubes, as for the pre-amp section they can be of any brand

sonoragazzo said:

peter_rooter said:

Excellent, thank you.

I don't need to Bias the replacement tubes do I?

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For the power section you will have to get Mesa tubes, as for the pre-amp section they can be of any brand

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Not correct - you can put any brand of power tubes in but..............
You will probably void the warranty if you stick in another brand and there's another problem that requires it be sent to Mesa Corp for repair.
They might look at the non Mesa stamped tubes and try to avoid warranty blaming the different tubes - even though you might have better quality ones installed than the stock Mesa JJs :mrgreen:

You don't need to bias any tubes on modern mesa amps - doesn't matter what brand they are.
If you're getting alternate power tubes just make sure you get a matched pair or matched 4 - all good tube retailers do that routine anyway.

Monstercastle said:

Pretty easy. Disconnect the reverb tank, remove the screws in the top, slide the chassis out the back of the cabinet. Reverse to assemble. Power tubes can be changed without removal from the cab, but the preamps are much easier with the chassis removed. Less chance of buggering it up. Keep fingers and tongue out of the exposed electronics.

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Well it's not easy at all on the Mark V 25.
Getting to V1, V2, V3 is very difficult even with the reverb tank out plus...........
You need a special right angled screw driver to get to the reverb tank screws and............
the back left side screw is very difficult to access even with a special tool - there's about a 1 inch gap only.

I couldn't find a tool that would fit in the gap.
I gave up after an hours fiddling with no luck trying to remove the back left side screw for the reverb tank.
And removing the whole chassis is just a bigger PiA.
I'm just gonna pay an amp tech to do it which is annoying just to replace V1.
That's the disadvantage of small & light weight

You simply disconnect (not remove) the reverb tank, and remove the top screws and slide the chassis out leaving the reverb tank in the cab. I think Authorized Boogie also said on prior threads that you can just remove the front trim panel.

Monstercastle said:

You simply disconnect (not remove) the reverb tank, and remove the top screws and slide the chassis out leaving the reverb tank in the cab. I think Authorized Boogie also said on prior threads that you can just remove the front trim panel.

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Can you please provide link to this prior thread.
Only youtube video I could find was for a Mark V (not 25) and said the front panel trim screws only removes the cover material & not the wood panel underneath.
I removed those 4 front grill screws and this appears to be correct - the wood panel would not move.
This same video also shows you can remove the reverb tank (on the Mk V) but you need this special screw driver.
https://www.youtube.com/watch?v=QbhAYpjJrrw

And I can't find a right angled screw driver that will fit in the 1 inch gap on a Mk V 25.
The reverb tank screws on the Mk V 25 (1 in each corner) are in a different location to the big Mk 5 - making access to them much harder.
The problem is getting to V1 - which of course happens to be the blown preamp tube on mine :mrgreen:

There's a reply here from Authorzed Boogie about the 5:25

http://forum.grailtone.com/viewtopic.php?f=33&t=70602&hilit=Remove

Monstercastle said:

There's a reply here from Authorzed Boogie about the 5:25

http://forum.grailtone.com/viewtopic.php?f=33&t=70602&hilit=Remove

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hey thanks but doesn't help at all for the Mk V 25.
The big Mk V is real easy compared to the tiny V 25.

Mesa Boogie Authorised guy says
"Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!"

Great - HOW

I've tried - removed the 4 screws - the wood panel won't budge and I'm not gonna bash it with a hammer.
And which way would it pop out? - inside or outside.

All too risky & difficult for me - I've taken it to a good amp tech / authorised Mesa repairer to do.
I'd rather pay a little and get it done professionally without risking damage to the amp.
V1 is a real PiA in the V 25.
This is the price you pay for extreme light weight & small size

In the link I posted the discussion turned to the V:25 half way down. Authorized Boogie said: "Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!"

Monstercastle said:

In the link I posted the discussion turned to the V:25 half way down. Authorized Boogie said: "Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!"

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yeah I specifically talked about that comment in my post above yours on 16 Oct.
I said

"Mesa Boogie Authorised guy says
"Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!"

Great - HOW

I've tried - removed the 4 screws - the wood panel won't budge and I'm not gonna bash it with a hammer.
And which way would it pop out? - inside or outside."

Should be able to tap the front panel out from the back after removing the screws. I'll try it on mine tonight if I have time.

Monstercastle said:

Should be able to tap the front panel out from the back after removing the screws. I'll try it on mine tonight if I have time.

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ok thanks
I tried on mine, tapped wood panel with some force from the inside in a few places without success.
Decided not to try to force it

Sorry, didn't get home in time to try it last night. Not sure if you tried, but it's actually pretty easy to just pull the entire metal chassis out of the head cab. This is how I did it when I retubed. You just have to disconnect the reverb tank connection, remove the 4 screws on top by the handle, and slide out the chassis carefully out the back. Reverse the process to put it back together.

Monstercastle said:

Sorry, didn't get home in time to try it last night. Not sure if you tried, but it's actually pretty easy to just pull the entire metal chassis out of the head cab. This is how I did it when I retubed. You just have to disconnect the reverb tank connection, remove the 4 screws on top by the handle, and slide out the chassis carefully out the back. Reverse the process to put it back together.

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ok thanks very much - will do this if there's a next time for tube replacement :mrgreen: