Studio 22+ loss of output

[tonejam]

Lately, I've noticed my 22+ isn't cutting the mustard, in a band situation. People used to be amazed at the guts it had, and I used to boast that it could give a Twin Reverb a run for its money. That certainly isn't the case these days.
My first thought is capacitors, but my tech, who is highly respected, and makes his own line of highly thought of tube amps, discounts this. He says if the amp was made in the 60's, sure it might need caps, but not mine. I think I'll try replacing all tubes as my first step, but what else could it be? Any ideas?
thanks folks.

 

[MichaelC4]

I think I'll try replacing all tubes as my first step

Do it!
Sounds like a tube wearing out.
New tubes will bring back the balls.

Also, clean the pots with DeoxIT F5.
And clean the input jacks with DeoxIT D5. Maybe even the tube sockets.

I've done all this to my 50+ within the last year and it seems to be in tip top shape.

 

[zoldt]

I have a question along the same lines... I have experienced the power output loss from my .22 as well (works fine for 10 minutes then power dies (cuts off to 1/2 or 1/3 volume on lead channel); turn off and come back later, it's back to full volume, but again only for ~ 10 minutes). I have read through these boards and will try what seems to be the common solution of cleaning the input/output jacks in the effects send/return loop first, but....
I also bought matched replacement power tubes directly from MesaBoogie website. I know the .22 is supposed to be a fixed bias amp so you can just replace power tubes and go (provided they are MB tubes specifically for the .22), but my .22 (I bought it used) currently has Groove tubes all the way around (power and pre-amp tubes). I'd just be replacing the power tubes only, but since I bought this used and do not know the details of what was done when these groove tubes were installed, how do I know for sure that I don't need to have a tech look at it to confirm the MesaBoogie tubes are biased correctly once they are installed? The Groove tubes EL-84's currently in there are labeled with a "5" number on them, if that's of any help; I think that number refers to what bias level they are expecting to be installed "into", and I don't know whether that number correlates correctly with the MB 6BQ5's that I got (MB sells only one version of this tube, while replacement Groove Tube EL-84's come in a range of numbers). I'd sure like to just drop the new ones in and go, but I paid $500 for this amp and don't want to do something stupid. I would say there are not a whole lot of hours on this amp after I bought it (I'm a home weekend/casual guitarist) but the drop-out didn't happen for the first ~2 years of ownership. Thanks, -zoldt

 

[swbo101]

I have a question along the same lines... I have experienced the power output loss from my .22 as well (works fine for 10 minutes then power dies (cuts off to 1/2 or 1/3 volume on lead channel); turn off and come back later, it's back to full volume, but again only for ~ 10 minutes). I have read through these boards and will try what seems to be the common solution of cleaning the input/output jacks in the effects send/return loop first, but....
I also bought matched replacement power tubes directly from MesaBoogie website. I know the .22 is supposed to be a fixed bias amp so you can just replace power tubes and go (provided they are MB tubes specifically for the .22), but my .22 (I bought it used) currently has Groove tubes all the way around (power and pre-amp tubes). I'd just be replacing the power tubes only, but since I bought this used and do not know the details of what was done when these groove tubes were installed, how do I know for sure that I don't need to have a tech look at it to confirm the MesaBoogie tubes are biased correctly once they are installed? The Groove tubes EL-84's currently in there are labeled with a "5" number on them, if that's of any help; I think that number refers to what bias level they are expecting to be installed "into", and I don't know whether that number correlates correctly with the MB 6BQ5's that I got (MB sells only one version of this tube, while replacement Groove Tube EL-84's come in a range of numbers). I'd sure like to just drop the new ones in and go, but I paid $500 for this amp and don't want to do something stupid. I would say there are not a whole lot of hours on this amp after I bought it (I'm a home weekend/casual guitarist) but the drop-out didn't happen for the first ~2 years of ownership. Thanks, -zoldt

Fixed biased Boogies will take any middle rated tube. The '5' on your Groove Tube is middle rated. Actually I believe Boogies will take GT rated between 4 - 6. So if you like the sound the GTs give you get another with that rating. You can also buy tubes from a reputable tube dealer like tubedepot.com and tell them you need a middle rate tube for you Boogie 22 and they will set you up.

Also all tubes sold by Boogie with their label are middle rated, so your good to go there as well.

 

[zoldt]

Thanks so much swbo101, you gave me the confidence to go ahead and install the new output tubes. My same problem showed up after 10-15 minutes of playing (reduced power and intermittent cycling between normal and reduced volume, crackly like a bad cord connection or bad potentiometer). Tried two different cords and two different guitars just to make sure it really was the amp. I started tapping pre-amp tubes and found that V2 really “sang” when I tapped it (so did V1, but not as much). Luckily I had ordered a single pre-amp tube when I bought the output tubes so I replaced V2. Once I started playing again, the amp was giving significant feedback, even with guitar at 0 volume or even unplugged. After 10-15 minutes of playing, I noticed the feedback was gone, and I hadn’t had a power drop-out issue during that time. Hoping it’s fixed.
An interesting thing written inside the amp was (as best I can tell) “Plate wired Mod. 8/93 M.S.” (See picture.) Anybody know what that is? Ok, I can't figure out how to upload the picture.

 

[McBarry]

Studio 22 are well known for thermal problems as they get bloody hot in there, and everything is on the one PCB AND it's machine soldered/clipped so tolerances are very fine.
I've repaired one with actual cracking of the solder of components - esp towards the rear of the PCB which is directly above the power tubes..

Might I suggest a thorough cleaning and re-tensioning of all the tube sockets, all the jacks, Deoxit pots as earlier suggested and carefully inspect the board for dry joints.

For pics, upload them to an external site like Photobucket, and then post a link in your post.
Here's a pic from my photobucket account to show two dry solder joints on a Studio 22. The joint was right next to the EL84 socket..
Notice the darkening around the area.. from memory it's the B+ dropper resistor..

 

[zoldt]

Thanks McBarry, here are links to two pics from inside my .22. The loss of output came back (after replacing preamp V2 with a brand new tube). I replaced V4 (reverb) with the tube that was in V2. Haven't tested it out yet, but I am not confident this is the answer. Anyway just looking at the board I would say there are a lot of questionable/dirty solder joints. Also still wondering if anyone knows what the "Plate Wire Mod" (see picture) might be.

http://s1367.photobucket.com/user/zoldt/media/IMG_1810_zps48814ec6.jpg.html
http://s1367.photobucket.com/user/zoldt/media/IMG_1811_zps448e23d9.jpg.html

I ordered Gerald Weber's "All About Vacuum Tube Guitar Amplifiers", hoping it has some practical trouble-shooting suggestions; two other books I've read provided more general background info.

Update 6/19/13: More troubleshooting: Played the amp with a box fan pointed directly at the back of the unit, and the power dropout didn't happen until I turned off the fan. In fact I could somewhat control the dropout by toggling the fan on and off (abrupt power attenuation starts within a couple minutes of the fan being off, but recovered 3 out of 4 times after turning the fan back on). I figure I'm going to play the unit disassembled until the dropout happens again, and then systematically cool each discrete element with a shot from a compressed air can until I can pinpoint the problem. If it's a bad solder connection it will be harder to pinpoint this way. I hope nothing explodes in my face from cooling off to swiftly; I'll stay away from the tubes but everything else seems fair game. Somebody stop me if I'm doing something stupid. (!)