Mesa Boogie DC-3 with Red Plating Tubes and Bad Reverb (AmpMechanic
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- čas přidán 9. 02. 2019
- In this 11th episode of AmpMechanic, David repairs a Mesa Boogie DC-3 with a serious red-plating tube issue along with a problematic reverb tank. As David digs further into the repair, he discovers a bit of a pattern that makes sense once he asks the owner a few questions. So, get your pencil erasers out. You'll need them for this repair.
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An extreme pleasure watching your exceptionally in depth and professional videos. Thank you!
Nice video. Inside of RCA jacks can be cleaned with pipe cleaners. You can use demineralized water to remove salt followed by alcohol and then a shot of solvent cleaner. Follow this by a hair dryer to remove all moisture. If oxidation on the shell is really bad, switch from a pink pearl eraser to an ink eraser. They are rougher and more aggressive.
Thanks Mike. I will have to write those tips down! I knew about the harder eraser one. I just couldn't find any laying around! I did clean a bit inside with one of those little brushes for cleaning braces. It's just like a pipe cleaner.
Woot Woot! Great video!
Thanks for the continued (and great) feedback @FWR.
I enjoyed the video. I actually own a dc3 and just last night when I was playing through it 2 of the power tubes started red plating. I've had the amp for about 7 months and this is the first time that its happened. I ordered just 1 pair of mesa boogie tubes for it today. Hoping that will fix my problem
Did the new MB tubes fix your problem?
The pouch is actually for the foot switch and cable.
oh wow! I didn't know that! Thanks for that bit of data. Will have to remember that in the future.
@@AmpMechanic Just sent back a Express 525 due to bad HISS just on the clean mode but not on crunch mode of the same channel
O L means out of limit, not open line. you can get O L if in the wrong range also.
The problem is caused through bad continuity of the reverb tank electronic boards. They are mounted to the tank with 2 rivets that are supposed to contact both the board that they pass through and the external tank housing providing a contact between the two.. This is the only way the boad makes this contact with the housing. way to do it is to soler a wire from the centre connector on the board to the tank housing and issue is gone. you now have continuity and the correct ohms. do this for both sides its a 5 min job.. sorted.
Hi Dave...another good video by you. I've got a Fender Princeton (RI) and has problem with one power amp tube...started internally arcing.......had similar issue with other matched set I installed prior to this....same socket. Got a new set of matched tubes but will have to poke around the socket area of the 6v6's to see WTF is going on as something may be amiss ! I re-biased the amp and I usually don't run it "HOT". Will let you know on the outcome once I get things on the bench...again ! Got new matched set from StewMac.......different tube mfr !
@tomk1atl: Questions I have (1) is the fuse the right size and is it blowing? If the fuse is rated too high, it might not be blowing when it should.. but if it's the right size and not blowing, at least that's a good sign. (2) Are you seeing any signs of arcing on the tube socket pins or if it's just inside the tube itself. You might see some burn marks and that might be indicative of a short in the socket's wiring (3) Have you used a multimeter to run some simple tests for shorts in the tube? Also, two suggestions on safeguards....use a current limiter when powering the amp up (it usually illuminates if you have a dead short) and power up gradually with a variac. Disclaimer: Amps are thoughtless, emotionless, and opportunistic murderers. As soon as they're given the chance, they will kill you. Any advice of mine you put to use, you put to use at your own risk of death.
I don't have any issues with blowing fuses, etc. I have a variac but this amp has been in service for about two years now. I have a reverb issue with it oscillating when rev knob turned more than "6". This may be a tube issue. I'll build the current limiter than Uncle Doug uses...smart idea ! Been working with this stuff for many, many years.......SAFETY is the #1 concern here for sure !
When I measured a new tank, the measurements jumped around for unknown reasons to me. Cables were good. Then it stabilized. Maybe the transducers need to stabilize.
Also, what's your take on the symptoms of A reverb transformer going bad? Blessings, Jim.
Hello, I have a question: does this amplifier engage like this all the time? Is there any way to fix this? I have the same amplifier and I also have feedback all the time. If so, please answer this question. Thank you, best regards
G'day... mate I have a Randall T2 amp head that suddenly has very low volume on all 3 channels... I've tried changing all tubes, nothing... different cables on amp and various guitars, nothing... sprayed tube sockets and input jacks with contact cleaner... nothing... took it to a local guitar shop repair guy a while ago... still not fixed but he seemed clueless so I won't even bother taking it back to him... Funny thing is, when I push the Loop On button on the front of the amp most of the volume returns, but still sometimes cuts in and out slightly but it is much much better than having the loop button off. My setup is straight forward to produce the issue... guitar plugged straight into the amp front jack, nothing else that could cause this... Sry for long msg.. any idea what it could be?
I did some minimal Googling of the T2. That's a hybrid (tube/solid state) amp with a bunch of mosfets in the circuit. I looked at the user manual very briefly and did not see a "loop on" button. Maybe that's on the footswitch? Anyway, once we're in solid state land, it's nearly impossible to diagnose the issue remotely. But, if I had to take a wild guess, the circuit probably forks in two directions.. one branch (the main branch) keeps heading for the output while the other branches off to the effects loop, picks up any external effects, and then returns to the main branch. My guess is that you've got a bad component or a short in the main circuit between those two points. Using the effects loop could be bypassing that flaw. I don't have the schematic. But one question is whether you lose the benefit of the tone stack when the effects loop is activated and you're getting sound? This might confirm my suspicion.
I won't down vote the video but I have to disagree with what you said regarding Mesa's biasing for this particular amp. My experience: I got a DC-3 combo brand new in the 90s. I happened to get a service plan with it. Playing at home I noticed that after about 20 minutes I started to hear a bizarre kind of distorted channel bleeding in the the clean channel. Anyway, I could re create the problem regularly, so I sent it in to get fixed and got a loaner. Same amp. Would you have guessed the same exact thing happened with the loaner. When I got my amp back it had nice new tubes and didn't have any issues for about a month. But the issue eventually came back. The only "fix" I ever did was to install a 120v fan into the chassis. About 20 years later and I'm using the amp again and getting the same issues. This time we have the internet. So I find out there are a LOT of folks having over heating issues with this amp regardless how they set the tubes up. It's gotten to the point where a few people came to the same conclusion independently. One tech on YT demonstrated how the EL84's were running way beyond spec on an amp that had several signs of overheating. I'm convinced this amp just had at least 1 design flaw. I love the brand. I'm a huge fan of Mesa and their heritage but I think they just dropped the ball on this amp and discontinued it accordingly. I just wish they had acknowledged this and put out a service bulleten for a fix. Because running stock these do not have Mesa reliability unless you're to treat your tubes as fuel.
I certainly cannot argue with the sort of pattern you spotted when doing searches on the net. In the end, you can always do some surgery and rebias the amp to run cooler (and not require Mesa Boogie certified tubes). I asked the owner of the one I fixed if he wanted to try that. But he decided to wait and so far, has had no problems with the amp (and it gets played daily by his son who is learning to play guitar).
Not familiar with this circuit, but 400 V is pretty normal voor EL34. Standard Marshalls like the 2203 have around 425 - 450 vdc on the plate. What do you mean the tubes are.pushed beyond the limit?
El84
"this amp will probably come back for repair again" is the mesa moto. trouble free? mesa? you have no idea what you are talking about .maybe 30 years ago. i have 3 mesa amps:2 lonestar 212 combos one 8:88 bass head about 3 years old every 2 gigs there is a problem. redplating power tubes ,noises ,fuses burning up input tranformers ....mesa are not for beginner techs either be very careful you need the warranty on these amps don't do it yourself .selected tubes for the amp model? there is no such thing(but used to be in the early days of fender and rca tubes like the first 6l6gc or 6v6gt ). all the tubes that come stock on mesa amps today are made in china (shhsshhh it's a mesa secret they don't have 'made in china' on them only a mesa logo)by shuagang (the cheapest lowest quality worst sounding tubes available today- jj sounds nicer sovteks last longer and have more gain ). mesa has a color code system and they sell in pairs so if you want to swap the tubes on the 8:88 you have to get 4 matched pairs with the same color code(blue is high gain on my tube tester they also run very hot so not recommended, grey and green are medium gain not sure about the other colors it's another mesa secret ). the pouch in the back of the amp is for the footswitch and\or power cord. i would not carry tubes inside an amp and expect them to work, but i would carry extra fuses and aspirin you'll need them. it's funny they named an amp "strategy" -the best strategy is to avoid new mesa amps. and the e7 chord on "always with me always with you" is wrong....
Thanks for your feedback Yaniv. Of course, I cannot dismiss your personal experience which sounds like it has been problematic. I can only speak for my experience with this amp that I repaired and what I do know is that the owner is still playing it daily without any problems. Regarding Mesa's white-labeling of tubes (Chinese or otherwise), I'm still pretty sure my educated guess is correct that they're picking (and matching) tubes that run on the cool side to begin with so that they can be pushed harder than off-the shelf matched sets. In other words, you can't just go buy any matched set (although, you could look for a matched set that runs cool). Even the more professional tube retailers want to know if the tubes you're buying are going into a Mesa Boogie. Anyway, I'm sorry you've had such a rotten experience with your MBs and wish you luck with whatever amps you end up using in the future. Thanks again for replying.
@@AmpMechanic the blue coded mesa branded power tubes run very hot that's a fact.they have tubes that run cooler but they don't give information about the meaning of the colors just advise you to use matched sets.they make you use theyre power tubes otherwise you lose warranty.an honest company would label high gain medium gain low gain so people can understand but then again an honest company wouldn't erase "made in china"
i live in a very hot climate so amps with heating issues don't survive.it's getting worse with time dc3 is far better than a lonestar mark 3 is much better than dc3...having the tubes mounted on the pcb is poor engineering.mesa amps makes you break the bank than they break your back.the question is how much time are you going to waste on fixing one amp? is it worth it? you work for free but another guy would tell the costumer"it will take too many hours and cost a lot so maybe it's not worth fixing"
@@AmpMechanic you can buy a "non mesa" matched set but first you have to use a tube tester see what's the gain level and other ratings on those crappy chinese power tubes that came with the amp than use tubes with the same ratings since it's fixed bias.if they are using such a hi tech tester how come all the 5y3 rectifiers they used on lonestars 1st gen went bad and they replaced them for free? robotube went for lunch?
With all due respect, the "mesa tubes in a mesa amp" stuff is a transparent attempt to capture repeat sales pure and simple. Maybe when the amp is built it might have some merit, but after a few years worth of component drift you sure will have to bias them, and it can be done in a couple of ways with some caveats-assuming you have the proper bias probes. 1) have a range of power tubes properly set up on your maxi matcher with desired current ranges so you don't have to do anything 2) install a pot in place of the bias level set resistor and trim to suit or 3) parallel a selected resistance value across the bias resistor to adjust its value to suit. When you've done all this and it's still red plating then you-not me-get to change out the power tube plate coupling capacitors because at 400v they're under spec for the job they're being asked to do.