Mark V maintenance

[Dr.Jackle]

Hi,

I've never opened a Boogie amp, and just learned by first hand experience why many people whine about this matter. So, is there any fast way to get clear access to V1 preamp tube? Even though I'd remowe all power tubes, there's still a transformer in my way so that changing the tube is unreasonably difficult. The only way seems to remove the amp from it's chassis? If so, how do I get it out? I unscrewed the metal grill on the back of the amp, the metal laths on top of the amp, as well as the handle and still the amp was tight in the chassis.

 

[golfnguitarz]

I have done it by just removing the one power tube by the transformer. The sleeve is a little tight around the V1 preamp, but to see how to undo it, try gently pushing down slightly and twisting the V2 or V3 sleeve to see how it works. The first time was difficult on the V1, but it gets easier once you see how it works. Just go slow and make sure your amp is unplugged.

 

[>Photi G<]

If you really wanna remove the entire chassis, make sure you disconnect all other cables, such as the reverb, fan (and maybe detach the fan altogether), and power (you'd better :evil: ). Next, unscrew the chassis bolts from the top of the cab. The handle shouldn't be necessary. Make sure there isn't anything catching the amp from behind the grille (that means remove the grille and check. Then, I find it easiest to hold the amp by the PT, and the OT which are at opposite ends of the chassis. Slide the chassis out the back of the cab, and set it down on a bench. The following step is SUPER IMPORTANT: Take some gut shots, and immediately post them here! :mrgreen: Then flip the chassis upside down on a clean surface, and replace the desired preamp tubes.

 

[Dr.Jackle]

Hehe, thanks. I changed the tubes without removing the chassis. The V1 sleeve was a real pain in the ass.

BUT, I didn't cure the problem yet.

First I had some mosquito-like squealing with CH3 Mark IV mode, and it appeared in a minute when I started to play. CH3 was a bit noisier than before so I of course assumed that the problem was with a preamp tube. I tried to swap V1, V3 and V6 but it didn't cure the problem. Then I noticed that when I flipped the standby to on, the middle pair of power tubes give very clear blue/purple flash and then start to glow purple. Those are the tubes in use all the time as I run all channels in 45W mode. When I switch to 90W, all the power tubes start to glow purple and in 10W mode the two 6L6's next to the rectifier tube glow purple. I've understood the purple glow is somewhat normal, but what about the flash in the center tubes wen I flip the standby on? I thought not, so I replaced the center pair with new ones (the yellows) but I still get the flash. So, is this normal?

Now V1 and V3 are replaced and the mosguito-like squealing is gone (I hope so, at least it didn't start after that), but the CH3 is still pretty noisy, and CH1 (especially in tweed mode) is noisier than CH2. Then also as I tried to track down the problem, I noticed that the more I add reverb to CH1, the amp starts to hum very much, so that reverb on ten it's unusable. Same procedure gives small hum with CH3 and no hum at all with CH2. I believe this is not normal?

I'm going to replace one at a time rest of the preamp tubes, but given all these symptoms, can this be just a tube problem?