Mark V Head - Dead simple tube swap instructions

[Monstercastle]

I really don't see what the fuss is about with tube swaps in the Mark V head. I bought a full set of tubes for spares, and upgraded to the SPAX7's in all the pre-amp spots. I don't expect to change them for quite a while again, and they are just dead quiet in my Mark V:25. So the big boy got the same treatment. I was fully expecting to pull the head from the case, but didn't need to.

Here is my step by step:
(1) Set the head (cooled down) upside down on the table on a towel or something.
(2) Remove the tube guard
(3) Remove the power tubes and rectifier tube. (I labeled mine with a Sharpie per the position chart in the manual)
(4) Twist and remove the large shield tube from V1
(5) Remove V1 noting the position of the pins for easier orientation of the new tube.
(6) Install new V1
(7) Reinstall V1 big shield (no problem with clearance in my experience)
(8) Repeat for V2-V7 (always noting pin orientation for easier reinstall)
(9) Reinstall Power tubes and rectifier
(10) Reinstall tube guard

Honestly, I was surprised at how much room there was. I have big hands (I'm 6'7" 350lbs) and had no issues whatsoever. The whole process took less than 20 minutes, and that was mainly because I labeled all the pre-amps I pulled with their location for storage.

Now the little Mark V:25, that you have to pull the chassis out of the box for.

 

[Dreamtheaterrules]

I have a V25, so I'm not looking forward to the first time I need to swap. But I think that the negative remarks come from people that are used to swapping tubes easily in some of the full sized heads with tons of space inside. When I tube roll, I like to put one tube in, play for a while, shut the amp down, quickly change one tube, and play for a while, then repeat. Then I get a real "exact same settings/same guitar/same time" test. Once I have a general idea, I start to leave that tube in for a few days and roll a few guitars through, hit it with a boost, etc.

When all you have to do to accomplish this is turn the amp around, reach in and change the tube, and you are back up and running in less than a minute, this tube testing is pretty easy. When you have to detach every chord from the amp, take it down from the speaker, remove 3-4 tubes to get to the pre-tubes.... it starts to be more of a hassle.

When you have to remove the amp from the head shell... IMHO, that's unacceptable. The small size immediately becomes more of a liability than an asset. I admit I've had my V25 for a year and haven't flipped one tube yet. I keep hearing a Tung Sol in V1 will be great. If it's really as much hassle as I've heard to swap a tube or two, I may never try it til it's required. I love the amp so much I'll obviously accept this. But it is a hassle. And as much as I love the size, I've looked in mini amps before and thought "make this 2" higher and maybe 2" wider and you have easy access to the tubes, and it's still small in size." In fact, one of the appealing things about some of the metal cased mini heads is, that the whole cage lifts off giving easy access to tubes. I'm getting ready to test some tubes in my TA15 and my V25. I'm guessing that one is going to be way more fun than the other...

 

[jmontgomery]

Lay the chassis upside down and swap away.

 

[Monstercastle]

I used to tube roll in my former amps but have no intention of doing so in my Marks. I did get the Spax7's for all preamp spots in both heads though. The Mark V and 25 have the tones I was chasing with my former amps, and they sound that good without worrying about this tube having more magic than that tube and all that. Now I'll use the time playing, and knowing when I do have a tube fail, the replacement will bring me right back to happy. I'm done chasing that dragon. 8)

 

[bandit2013]

I have been down this road many times. Always had a problem getting the Long tube shield back on and it resolved itself as I rounded off the tabs and had to replace the shield. (bought several to keep as spares). For tube rolling - experimentation it is much easier to remove the amp chassis from the shell and invert onto the cab. I usually borrowed the reverb tank from the Mark IVB since it was easier to put back in.

Easy thing to remember about the preamp tubes, all of the tubes will face in the same direction except V3. The gap on the pins will face towards the front of the amp and V3 is mirror to V2. Rectifier tube is closest to the AC power cord.

 

[Monstercastle]

Always had a problem getting the Long tube shield back on

Were you trying this with the power tubes and rectifier tube still installed? With them out I could drive a truck through there, at least on the head.

 

[bandit2013]

No, there is no way my hands would fit in the space with the power tube in place. Besides that, since I damaged the long shield (also scratched the tube) I found the standard length shields to be much easier to install. The long shield is nothing more than the short one with an aluminum tube attached to it. Its only purpose is to indicate there is a tube behind the OT. However, with the Roadster head I can reach it with ease (I know, not the same challenge). My troubles with changing preamp tubes in the Mark V head are over. I converted the head into a combo. Now have easy access to all tubes.

If you plan on doing a tube roll, my recommendation would be to remove the chassis and invert it on top of your speaker cab. Leave the shields off and swap preamp tubes as needed without the wait of letting the power tubes to cool down. Once you are done, put it all back together. It is best to have the reverb tank in the circuit when doing a tube roll. That has its own challenges to re-install if you remove it from the shell. Use q-tips (with one end removed) placed in the T-nuts and assemble the bushings over the sticks, carefully place the tank over the assembly, remove one stick at a time and replace with screw. Quite easy.

Once you have changed tubes a few times, the hassle becomes less of a challenge without having to remove the chassis. I am not saying there is any issue with your technique, if it works, great and thanks for sharing. 8)

 

[Monstercastle]

Yeah, no worries. I was just surprised at all the posts about how difficult getting to the pre's are in the Mark V head, broken tube shields, people cutting open the front panel for quick access, etc, when the entire process of replacing all 7 pre-amp tubes took me 20 minutes without having to pull the chassis. And I'm 6'7, 350lb with big hands. Really seemed like much ado about nothing. Now my V:25, yeah, that's another beast entirely if you try to do it without pulling the chassis.

 

[Authorized Boogie]

Now the little Mark V:25, that you have to pull the chassis out of the box for.

Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!

 

[Monstercastle]

Now the little Mark V:25, that you have to pull the chassis out of the box for.

Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!

Thanks Authorized for the tip.

 

[bandit2013]

Hey, that's good to know. Too bad the Mark V head was not similar. I had no desires to modify the shell to accommodate the tube swap. My issue with the extended tube shield was getting the spring centered on the tube. Using one of the short shields resolved that one. The spring in the extended shield was biased to one side and not centered in the bore. Made it more difficult to install resulting in damaged tubes or eventually ripped metal detents on the bottom of the shield. Sometimes it would go one with ease and I could do a tube change in a reasonable time. Most of the time I would spend just 45 minutes to get the thing back on. It took me less time to pull the chassis out, swap tubes, clean out all the metal chips from the shields sliding against the chassis and reinstall. If I was tying to locate a noisy preamp tube, I would do that with the chassis removed as it is easier to perform without having to wait for the power tubes to cool down.

 

[Dreamtheaterrules]

Remove the grill for access to the Mark Five: 25 preamp tubes! Thanks!

Thank you!

 

[Ytsejammer777]

Finally got around to performing some tube rolling this last weekend and this method worked great. I really had no issues getting around inside and swapping around preamp tubes!

I really don't see what the fuss is about with tube swaps in the Mark V head. I bought a full set of tubes for spares, and upgraded to the SPAX7's in all the pre-amp spots. I don't expect to change them for quite a while again, and they are just dead quiet in my Mark V:25. So the big boy got the same treatment. I was fully expecting to pull the head from the case, but didn't need to.

Here is my step by step:
(1) Set the head (cooled down) upside down on the table on a towel or something.
(2) Remove the tube guard
(3) Remove the power tubes and rectifier tube. (I labeled mine with a Sharpie per the position chart in the manual)
(4) Twist and remove the large shield tube from V1
(5) Remove V1 noting the position of the pins for easier orientation of the new tube.
(6) Install new V1
(7) Reinstall V1 big shield (no problem with clearance in my experience)
(8) Repeat for V2-V7 (always noting pin orientation for easier reinstall)
(9) Reinstall Power tubes and rectifier
(10) Reinstall tube guard

Honestly, I was surprised at how much room there was. I have big hands (I'm 6'7" 350lbs) and had no issues whatsoever. The whole process took less than 20 minutes, and that was mainly because I labeled all the pre-amps I pulled with their location for storage.

Now the little Mark V:25, that you have to pull the chassis out of the box for.

 

[Monstercastle]

Glad it helped.