Best Method of changing premap tubes

[cscotto]

Hello,

I just picked up a JP-2C. The is fantastic, but I have a microphonic/humming preamp tube. I think it is V1. I want to change out the stock tube for a Tung-sol. On my Mark V, I generally remove all power tubes, then squish my hand around the transformer to get to V1. Not fun, but doable.

The JP-2C has even less space for a good sized hand. I watched a Youtube video where removing the reverb tank made the job easier on a Mark V. Frankly, for the amount of work that took (you still had to remove all the preamp tubes), it theoretically seems easier to remove the chassis. So, two questions. For those that already changed preamp tubes on the JP-2C, what method did you use? Is there anything I should know before removing the chassis, tips, tricks, problems, or will it pop right out after I removed the four bolts?

Thanks in advance,

 

[cscotto]

OK, well, I will answer my own post in case it helps anyone else.

First, the tube layout is in the JP-2C allows easier access to the preamp tubes. V1, for example, is not stuck behind a transformer. I only needed to remove three power tubes to gain access to all the preamp tubes. I placed the head upside down on desk, reverb tank pointing up. This made lining up the tubes very easy. With the head upside down, it was also pretty easy to get those cans back on. I could actually get both hands inside the case to push down on the can with one hand and twist with the other hand.

All in all, the job was much easier than I thought it would be.

 

[GJgo]

...Or you could just unscrew the front cover. Voila.

 

[cscotto]

That is what I wanted to know. Thanks. I was trying to find out if you could get to the tubes by removing the grille cloth. You can't on the V, and I didn't want to try on the Jp-2C unless I knew it was possible.

 

[kramerxxx]

When I owned a Mark V, the first time I wanted try current preamp tubes in V1, I pulled the chassis out, removed the front grill, and took a jig saw and cut an access hole through the front. Cool to hear mesa is doing this in the JP2C from the factory.

 

[bandit2013]

No jig saw required with the JP-2C. You will need a long screw driver or wooden dowel to push on the cover from the inside once you loosen up the 4 screws. Face plate is tight and will need a little push to free it. No need to remove the power tubes to get access to the preamp tubes. Mesa listened and followed kramerxxx's fix for the "I cant reach the dang tubes" issue. I was going to do a write up with pictures but photobucket kicked the bucket and would not let me log on anymore. My hands cannot reach around the reverb transformer to reach V1 from the rear. Front face plate removal is the best method.

As for the Mark V head: I am clueless how one could remove the reverb tank on the Mark V without removing the chassis first. Perhaps the year may make a difference, mine was built in 2012 and the screws that hold the tank in place screw from the inside. Also try to get the tank back in would also be a task if the chassis is in place. I did think about making a change so I could drop the tank but it was much easier to convert my Mark V head to a combo.