That's It...This Amplifier is SATAN. (PART 3)

[@TheGuitologist]

NOTE: One thing I forgot to mention... Right before the guitar test, I had also changed screen resistors to 2W metal films and it still ran away, so not those.

[@hyperluminalreality1]

Hi man, did you happen to monitor the bias voltage on the output tubes in question to see if it varied while they ran away? Could it be parasitic oscillation on that half of the phase inverter? Test that by monitoring the AC voltage on the output primary while it runs away. An oscilloscope really helps in this kind of situation too. Mine is an ancient military surplus Kikusui COS6100M. 5 trace analog. Excellent amp monitor scope. I also have my UT61E and two Keithley 179A bench meters I got for $20 each. Multiple voltage monitors help diagnose also... Have you switched out the phase inverter and output tubes for known good ones or tested them on a tester?? You are shooting in the dark without some basic test data that is easily obtainable. Uh oh, Its not Friday... You will fix it, and get more entertaining video time your way too. I just like the "test your hypothesis with instruments" method as opposed to empirical parts changing based on an otherwise untested hypothesis, or theory. Quicker, and much less maddening. I am working on a 1980 Fender 140 right now. 6L6GC tubes in class B at 500vdc. Ugh. Point to point and a rats nest. Thanks again for all the vids. I let them play while working. better watch this one now. Yeah I posted before watching....DOH!

[@idiotburns]

The Guitologist good to check em

[@maxt8289]

Hi Brad. Not sure whether you already checked it, but try narrowing down where exactly your bias voltage is dropped. You are measuring at the sockets, but it could be anywhere in the signal path coming from the 47n PI-coupling cap towards the grids of the two EL84s. Alternatively you could rebuild the side that gives you trouble with a few wires omitting the pcb-part (starting from the bias node with the 330k bias res tied to 47n with a 220k grid stopper towards the g1s of the pentodes). If I recall correctly the max Rg1 for EL84s is around 300k for EL84s with fixed bias (Mesa used 220k+330k, but that is not the only thing out of spec in this poweramp).

[@idiotburns]

Yeah, OR2.3 even has a hard to see green band that is faded from heat it appears

[@MrUltraworld]

Please post part 4 , for the exorcism finale.

[@papakoho8184]

Some years back, a Mesa Boogie design engineer came home early and found his wife and an amplifier repairman in a compromising position on the couch. The husband did not kill the repairman. Instead he decided to make every day of the repairman's life a living hell. Thus we have the Mesa Boogie amplifier.

[@kristopher6031]

Lmfao

[@markhoskins]

I love Mesa amps. I have a few of them but honestly my favourite amps are the simple ones. I don't repair my amps but if they go down I need to get them repaired quick. I know I can take a handwired plexi, ac30 or classic fender amp to pretty much any tech and they'll know how to fix it. Designing with servicing in mind should be a priority for pro-audio.

[@geronimostade8279]

Hi brad, some suggestions from a technicians point of view: First off, there is no obvious reason to think, that the OT is shorted. While the amp idles, it represents a simple DC resistance of a few tens of ohms to the anodes. Anyway, there is a slight possibility of temporary shorts within the OT due to temperature changes that lead into RF oscillations. Some things you could check first. 1.) Disconnect the negative feedback and check if the bias voltage stays solid. -> If the problem still exists 2.) Pull the phase inverter tube. -> If the problem then still exists 3.) Check if the bias voltage also drops before the grid blocking resistors. -> If yes, you have some sort of bad connection from the Coupling cap to the output tubes or bad connection from the bias resistors to the coupling cap or a bad bias resistor. -> If the issue vanished 4.) I would also check the components around the Phase inverter. There is a slight possibility, that one half wave oscillates. Could be the PI tube itself, a bad Anode resistor in the PI or something in the tail circuitry, specially the 1Meg Grid resistors in the PI. I dont think the OT has any issues but you probably put me right. Good luck mate, Geronimo

[@josephzielke8775]

You could try swapping the transformer primary leads. After the swap if you see the opposite tube set red plating then you know it's the transformer.

[@Only1Shadow]

You can quote me on this: Engineers need arrested and sentenced to work on their own products.

[@UncleDoug]

I feel bad laughing, Brad, but your (all too familiar) frustration is exactly why I stick entirely with point-to-point circuitry. This video makes me even happier that decision was made.....years ago. Most "modern" amps are simply not constructed to facilitate repair. I sincerely hope you can finally fix this abomination and never see it again.....ever.

[@PaulinTaegu]

I have a feeling he let it get the best of him. Output transformer, I doubt it! Think of the symptom. 1/2 of the tubes RED plate, and that stays constant. OT test produced the same results for both sides. I think it is the coupling cap from the Phase Inverter for that pair of tubes. It warms up and begins leaking voltage from the Anode of the PI pulling the Bias voltage on the grids of that pair of tubes down. Coupling cap or caps for that pair of tubes need to be replaced, not the OT. Much cheaper too. I know this symptom, seen it many times. ;^) Damn Caps! LOL

[@TheGuitologist]

At least I can give people a laugh at my expense.

[@TheGuitologist]

See Part 2 for all that's been done already, Paulin. I already replaced the coupling caps.

[@PaulinTaegu]

Replace them again and use a higher voltage than called for signal caps. Use like 600V caps or higher if you got some in your stash! A little leakage when they get hot gives this symptom every time. ;^) I did learn this the hard way myself. LOL 8^)

[@PaulinTaegu]

I sent you an email with some pics. Check them out and see what you think. ;^)

[@benjikoorts4053]

"Just give me another Inch and a half" that's what she said!!!

[@TheGuitologist]

I was too pissed off to make such an obvious joke. It's the ISIS effect.

[@usoppbarbosa981]

@@TheGuitologist Hey !! i'm offended dude, i'll call the feds goddam !

[@robertkerns3488]

Yes, its true...satan is a female.

[@udertyrat]

We’re all thinking it bro 😎

[@scottshields3054]

I think you and my Dad would get along fine. He's a mechanic and everything you said about the amp not having enough space and having been designed by some a hole that's never worked on anything I've hear from him a million times about newer cars.

[@douglaswalther8489]

Thank god the FBI didn't come the day you were working on this amp!

[@TheGuitologist]

Hahahaha...like right in the middle of taking the board out!

[@barbmelle3136]

From Leo: You have my sympathy. Circuit boards with tubes in a congested chassis are the worst. I am glad to be retired and can turn that work down. The jerk that commented on your part changing has no understanding of the economics of troubleshooting, especially when the problem is intermittent. If the problem is usually one of 4 parts and the parts are 75 cents each, that is far cheaper to quick change all of the parts at once than the time to narrow it down to save the $2.25. You can only charge the customer so much bench time. Intermittent transformers can be really tough without a dielectric tester, but I only worked one place that had one of those available. You are more patient than me. Good luck

[@TheGuitologist]

Yes,yes,and,yes. You get it.

[@MrUltraworld]

Mesa sure does cram a ton of components into their amps. Not very technician friendly.

[@Stefan-]

Barb Melle Yeah, you have to commit to actually do something rather than spending the whole day just screwing around and if you have to rip out a cricuitboard that wont come out like that, you also tend to do everything at once rather than having to rip it out 10 times to replace suspect parts one at a time or resolder. If you work on your own stuff then you can screw around all you want, but if you repair things professionally then there is a limit for what the customer is willing to pay.

[@daveanderson5680]

I thought it was a bad tube.....glad to see you rotate the tubes. OPT makes sense....after all the plates do connect to the OPT primary. Something was pulling the tubes into redplating.....and You already checked bias circuit & screen resistors. I’d rather have a tooth filled than work on any amp with more than about 6 knobs.

[@ETILHK54]

Handcrafted by I$I$

[@bigfootingermany]

Danich Ivanov Hahahaha

[@toddflowers8052]

LMAO !

[@danashcroft961]

Nope, Californian flakes...

[@toddflowers8052]

@@danashcroft961 This was a reference to his visit from the F.B.I. but, you are correct.:-)

[@stevelacombe5291]

LOL

[@underpressureman]

Thanks for this Brad! I think this mesa series will help alot of people! Now to get my 50Cal+ fixed or run fast the other way!?! The friend who gave it to me got it from a guy who had it into a tech twice and the 3rd time it broke he just sold it! So it could be an easy fix this time or could be huge. Watch it be the output transformer lol!

[@randolphpatterson5061]

Years ago, a friend brought over a Mesa that was acting up. He never quite got to describing what was going on, but he started taking it apart before I could even get a listen. He said he thought it just had a bad preamp tube & he had a spare to install. Then we fired it up & it seemed to work okay, so I never did any troubleshooting. But what I saw was more than enough to convince me that I was gonna try to never have to work on a Mesa for the rest of my life. Everything was jammed together like a can of sardines, and there were little shitstorms of circuitry & components covering every square inch of internal real estate. If you ever have a chance to own a Mesa, ask yourself just exactly what they do that's in any way special or unique, in terms of playing tone & response, then ditch the idea and get any of dozens of other amps that sound as good or better in every way, cost half as much, and are ten times easier to work on when the time comes. Smith made his mark by originally modifying old amps by adding extra gain stages to get high levels of preamp distortion, and so they carved out something of a respectable reputation which seems to have lasted. But we repair techs don't think much of Mesa's rep, not in any way in hell. They're a big pain in the ass, and make a lot of us feel like simply closing up shop whenever we hear that someone might bring one in. Who the fuck ever really needed 20 knobs to twiddle, to just get up on a stage and put on a show? And why do all these amps have to be crammed into matchboxes? Nobody's ever had a Mesa that's actually lightweight anyway. There's no such thing. Fuck that whole outfit, it's some kind of cult for the very few who swear by them, who are rich & famous enough to have a perfectly good new amp arrive within a few hours of calling the factory. Leave me the fuck out of that cult of lunacy, no thanks.

[@dlunsford1980]

I had a Epi Standard on the bench a few years back giving me fits. I’d flip it upright and it would play, as soon as I turned it over to get to the board it would run away. Just by chance I was examining the tubes and noticed one of them looked a little off. The damn plate on one of the tubes was loose and when I flipped it over it would fall and short to the getter. I am talking maybe a 2 millimeters worth of movement. That repair sucked but man I was glad to figure that out and get it off of the bench.

[@johnstrange6799]

I had an amp early this year that had the cord cut off. Little nick in the stub of cord that remained on it too. No big deal, I just added a plug to the bit of power cord left on it and dove in to see what had gone so wrong that someone had to cut the cord off before discarding it. It wouldn't power on. I took it apart. I checked everything. I put it back together stumped. I figured I'd sell it cheap and let someone else figure it out. No one wanted it. So I took it apart again, and put it back together again, still couldn't figure it out. I tried to give the damn thing away... got no takers. I gave it one last shot by taking it apart all to no avail. Now I was going to throw this son of a bitch back in the trash where it came from and just be done with it, BUT not before I put it all back together one final farewell time. When I did reassemble it that final time... I heard the soft "Boom" of the damn thing powering on! I turned the amp around just in time to see the power light go dark on the front panel. So I turned it back around, and again "Boom" it powered back on. It was right then that I noticed with a sobering certainty that the whole problem all along was just the little "no big deal" nick in the cord that I had planed to deal with once I got the thing fixed.

[@normlenhart1310]

Hold up a Soldano SLO before it and chant "The Body of Mike COMPELS YOU!" Nothing can withstand an SLO.

[@jameswarren1831]

For plastic standoffs I take a small metal tube that compresses the arms. I personally cut up an old car antenna into a bunch of 1/2” pieces.

[@randolphpatterson5061]

Great tip!

[@udertyrat]

Makes me terrified to think of a Mark V repair...

[@bullwhipjohnson8247]

I can't wait to see Episode IV. The Transformer Cometh. Don't feel too bad. A former co-worker of mine, who worked on Stereo Amps and VCRs for years. And, had earlier graduated from a Vocational Tech School. Had to take a two year course specifically for Mesa Electonics. So, he could be Authorized to do repairs on Mesa equipment. Good Luck!🍀

[@TheGuitologist]

That sounds like a circle of hell I never want to visit, let alone live in.

[@Starcrunch72]

WTF--2 years...talk about selling your soul

[@worldofameiso5491]

I was thinking of buying a secondhand Dual Caliber DC10 combo. After watching this I don't think I'll bother...

[@Dogsrule777]

It’s like a daunting maze of possible culprits! It’s awesome watching you deduce and conquer man. Can’t wait the finale! 🤘🏽⚡️

[@mars6433]

@1:53 "You're a parts changer." ummm....yeah....that's what an amp tech does. duh.

[@robertcalkjr.8325]

Some people just get off on trying to get under peoples skin. Better to just ignore them.

[@shitfer]

@@TheGuitologist The troll in question has a channel we can all critique, right? That's what I thought. Fucking peanut gallery.

[@danashcroft961]

@@TheGuitologist Exactly the ones that are always there with "the advice" are the ones that have never done anything 9 times out of 10...

[@haasjeover123]

@@TheGuitologist Sometimes it just turns into looking for your glasses while wearing them :)

[@chuckschillingvideos]

I don't think there is one common methodology to tube amp troubleshooting/repair that works equally well for ALL known amplifier makes and models. Some amps are just "gotcha" amps that, unless you specialize in them, will seemingly defy all attempts to remedy their faults and issues. For some reason Mesa/Boogie seem to specialize in the manufacture of these sorts of amplifiers.

[@mikegubbin997]

Hi, Your channel has been very helpful for me, I've been fighting with a Roadster for 2 weeks on and off (as you do) another tech had it for a year b4 me and destroyed most of the evidence, and the pcb! Just fixed it (fingers crossed). I've been been building and fixing tube/valve amps for 45 years, so I feel your pain on this one. I have a habit, personally, of redesigning things I can't fix. The obvious culprit in your amp here has to be the high ohm resistors on the grids of the output valves going down to ground, I can't imagine what else would have caused your problem. sorry I didn't see your post 2 years ago, I'm sure I could have helped. Anyway, Great stuff! Please keep posting. Cheers. Mike

[@shanev7693]

Hey Brad just a tip to remove the the circuit board clips try using a pen with the ink taken out and just push down on the clip it will close the clip and you can pull up the board. Hooe this helps bye for now Shane

[@th3drizzl378]

nope stopped touching mesa stuff. not anymore. dealt with this once and never again. the one i had ended up being the actual board so in the end it needed a full rebuild and the board looked perfect there was zero issues you could see with the eye and it tested fine when cold.

[@rollacoastaride1937]

when in doubt, give Jim Marshall a shout, no gimmicks, no frills, the go to amps, and cheaper than all the rest too.

[@VegasCyclingFreak]

18:00 That's a cool diagnostic tool. Will have to remember that one. After doing every other possible thing (basically like you did) I guess by process of elimination you would have to end up with the conclusion that the OT was bad, but that neon bulb trick definitely helps to confirm that.

[@THUNDERWORX]

After the design was finished someone must have said, "it would be more fashionable in a smaller head." I always thought Mesa was well built, but this looks like a Chinese board crammed together with tube sockets soldered on. Everything about this design says, "I will overheat and melt my own parts given enough time."

[@grahamtownsend3751]

someone said you were just replacing parts? how the hell is possible to fix anything if you don't.

[@tommyconancoates7097]

Like really, if it's busted aren't you SUPPOSED to replace it Ahaha

[@niftykeentypedog]

The criticism is that he's replacing parts without knowing exactly why they're being replaced. I'm not saying that's always a bad tactic, but it definitely has its limits and can lead to epic repairs like this. Many grey-beard engineers like to laud their superior experience and knowledge over everyone else and this is just one way they do that.

[@tom474e]

Mesa's are notoriously difficult to diagnose.

[@vk3fbab]

If you don't replace parts what you need to do is come up with theories why it's behaving the way it is. You then need to test that the components you suspect are faulty are faulty or okay. This works well for a while but what about if every part tests okay? Well you need to come up with more complicated scenarios. So these could take the form of temperature or stray inductance, mechanical damage the list goes on. Sometimes it's faster to replace an entire section. The most expensive part of the repair is labour. Hence why a lot of devices are repaired at a board level. It's just cheaper and faster that way.

[@shitfer]

A Vulcan mind meld will diagnose.

[@jamescorvett]

i see the problem right off, made in Petaluma california j/k lol I'd prob pulled the board right off the first time around. But i'd also suspect the transformer is crapping out. added those heavy traces on the back look like they are pealing off the board. i'd say yelling at it but i think you've already covered that. Good learning experience though.

[@omarmolina207]

Hey Brad. This is bringing back memories of a MB Studio .22 that had all of the same kinds of problems except the red plating. However I had a similar redplate experience with a blonde Showman. So with the Studio 22 I eventually resorted to reflowing every solder joint on the board after repairing the EQ and recapping. The crosstalk/ghost noting you were having on the first video was identical and the culprit was the EQ and it's supporting circuity. With the Showman the problem was the output transformer. I could disconnect the negative feedback and swap the primary to plate connections. The redplating would jump to the other tube pair. That's how I definitively diagnosed the transformer. I noticed on your lightbulb flash test the the speaker was still connected. I believe that this gave the current a path through the speaker at 8ohms instead of the 30k path through the light bulb. Repeat your test without the speaker. You'll probably get flashes on both sides of the OT. The other thing about the Showman was that the redplating would only happen at higher voltage. If I had a lightbulb limiter or variac in series then it never acted up. This leads me to believe that the failure was thermal but intermittent inside the transformer. That's why it behaved most of the time and then ran away only intermittently. Another thing to consider if swapping primaries doesn't cause the redplating to migrate. Try 1k 3watt resistors on the screens instead of the 470s. Back in the late 90s there were a ton of New Sensor made 6V6s that would randomly red plate in Fender DRRIs. The accepted solution was to increase the screen resistor from 470ohm to 1k. Love your channel. Let's me know I'm not the only one out there digging through amps and figuring things out-sometimes the hard way.

[@pedrolourenco2707]

I had a similar problem on a Orange, it turned out to be a cold solder on resistor on the PI tube circuit

[@TheDyingScotsman]

Discovered you only recently, but I love your videos. The edits with movie clips makes me chuckle. I feel for you doing this, but man, I just wanted to say you're awesome!

[@mal2ksc]

Those 2 for $1 Sunbeam 9Vs are the shit, man. They work great in most pedals, and of course in meters which is probably what you mostly use them for. I only say that because you're "not a pedal guy". If I ever gigged on guitar (I did once, but it was kind of a stunt), I'd keep some on hand in case I couldn't eliminate power supply noise in some venue. Pop in a battery, do the gig (or several gigs if need be), and figure it out tomorrow. Belt and suspenders. Their shelf life is perfectly adequate too. Even though they don't have as much juice to start with as more expensive batteries, their self-discharge is pretty low so they keep what they have.

[@Starcrunch72]

I had (remarkably) a '66 Bassman that gave me fits like this a couple years ago. Replaced all bias components, screen and plate components, rectifier diodes, full cap job, every resistor that drifted was replaced--it still was running away. I made the decision that the replaced OT (a 60s Thoransen 50w TV OT) had been installed and the primary leads were shorting inside the bell. Oh yeah, the dingdong that installed that OT has to shave the inside of the cabinet for clearance. Ordered the $65 Fender replacement from Antique Electronic Supply and its been rock solid ever since.

[@rockyoyam8956]

I have the same amp... 18 years now... still works... cross my fingers!!!

[@danadrian2752]

Satan? Better call the FBI, Ghostbusters, and local pastor!

[@Scottie_S]

"How are ya, Lenny?"

[@TheGuitologist]

Satanus...that's latin for "Satan".

[@electroKrunch]

What do those fellers in Petaluma smoke??

[@jennysbloke]

This is edge of the seat stuff, Brad. It was like an episode of ER when you were in there taking readings. "We got a bleeder !"

[@TheGuitologist]

I see myself as more of a misunderstood, brooding House type.

[@jennysbloke]

@@TheGuitologist - That goes without saying, of course ! Mean, moody and smouldering. The housewife's fantasy 😶 ..... as long as she is into repairing amps, of course.

[@justinbouchard]

It also looks like alot of the traces on the board have gotten super hot. The paint that covers all the trace lines are all cooked. I've done that myself before when rewiring my phase inverter from a 12ax7 to a 6n2p and effed it up. Super glad I was watching the board because the lines got red hot almost immediately and bubbled all to hell. Luckily they didn't crack anywhere under the paint and still work but I thought I was going to have to just point to point my filament wires. Tons of love from Canada dude.

[@Torgo63]

Nice Video. You mentioned at ~13:57 that the board may have become conductive. That may not sound convincing to some people, but I've seen it, although not on a board that worked fine, then broke later. I'm not claiming this to be a R/C to this problem, but I think may be a useful example for someone else. I once found a board where two traces had a low impedance connection between them, despite being over 3.5 inches apart. It turns out that the fiberglass probably didn't have enough resin, and the solder wicked with capillary action during wave soldering. This looks like a wave soldered board to me (the wrinkles on the fat traces ~13.47 give me that impression). So, my point is that it may not sound like it, but it is possible for solder bridges to happen within PCBs, and over long distances.

[@spoonylove]

During the transformer test on the Mesa at the end, the light didn't illuminate, but the camera mic was clicking/popping. If that wasn't audible (guitar speaker noise), my arm-chair quarterbacking would suggest an EMI event (electromagnetic interfence). That would imply a reasonably significant current surge when the test was performed. What am I saying? Well, it might not be a closed book "the transformer is open circuited and dead". The test might be showing a false-negative result. Perhaps an o-scope on the secondary side would enlighten the situation?

[@TheGuitologist]

The noise was from the audio mixer and power supply being plugged into the same outlet.

[@spoonylove]

@@TheGuitologist ahh, gotcha. The fact that the power supply is inducing that noise into *anything* would imply a surge in current. Some in-rush is occurring, creating noise that we are hearing. Maybe it's simply the inductive load of the massive output transformer when the change in voltage is applied?

[@Narnyfied]

Hey man, hope you don''t mind me saying that I love watching you do battle with Mesa's. Really love watching these vids. My god they seem overly complicated!

[@Andy_Yates]

Still just a student of the amp arts here. It felt pretty good you listed everything I rambled on about in my part 2 comment, even the conductive board, but I never would have guessed the OT. Wildly frustrating and deceptive symptoms. Thanks for taking us along on this with you. Some of us will learn from your pain

[@spkay31]

This video is great to show why even high end amplifiers with a large number of features are really meant for people with enough money to simply replace them when they go out of warranty or with no problem sending them back to the manufacturer for repairs. Designing for high serviceability is something no manufacturer does these days except for the small boutique makers which also don't try to offer such a large number of features and tonal options on their amps.

[@richardruth3315]

Chasing your tail while trying to save the customer his hard earned money is never fun. I agree, you probably shouldn't accept any more (modern) Mesa amps in your workshop. I commend your perseverance here, though. Let your buddy in Indiana take the heartache of it all! The comments here are some of the funniest I've ever read, while these videos have been some of the most painful to watch. I have owned a DC3 for years now, and these vids have confirmed what I've been thinking for quite some time-- sell, sell, sell the damned thing! Any takers? Thanks for posting this vid, I sure learned a lot! Cheers

[@idiotburns]

That long PCB haha, that why screwdrivers are pointy, to stab your eyes out in frustration

[@gorillaau]

I thought screwdrivers are pointy so you can gouge the board when you are trying to release a stand off.

[@JohnGaray]

Your videos are great! also, your method of checking step by step is the correct way!

[@markanderson350]

I started think the same, I never heard of the neon light test. Love it.

[@aaronroberts3848]

If I rember correctly I had the same amp with the same problem. I believe I ended up putting two bias pots in it and told the customer it would need to be biased every tube change . Mesa boogie are deff a pain to do work on . The plastic standoffs can be a nightmare if u never delta with them

[@guitargamez7930]

How is a mesa messed up arent they supposed to me super super good?

[@miker252]

Sounded like the speaker may have been connected while testing the transformer. Would that load effect the voltage to the lamp?

[@Slew514]

You're getting an odd audio static spike when checking the output voltages from 21:36 to 21:56. Is this audible to you in the room? Could be grounding issues as you're bleeding off voltage?

[@TheGuitologist]

The power supply and audio mixer are on the same outlet.

[@avgjoegeek71]

That Money Pit laugh. When you can't just give a shit any more and have to laugh about it.

[@j-man72b72]

I died when that popped up, the kitchen wiring scene reminds me of the MESA. kzbin.info/www/bejne/jJnVhK2Lopitnrc

[@elvyfoster7455]

Sorry you are having the Mesa experience with this amp. For me as a viewer, this series of videos is great as a reminder why I should never buy a Mesa. I don't make enough to afford to buy a new one and judging from the problems with this one and others I have read and heard about it means that I should never buy a used one.

[@passthebs.1341]

Dunno if you got it... but, The 300 volt caps, Are they discharging normally? Another solution might be on the Plate Resistors... Same resistance or maybe even higher but than can absorb more heat and then perhaps some hi watt non polarized caps in shunt with the hi watt resistors. If that reduces the heat on the caps, then all you need is a rebias.

[@paulkielt9301]

I own a Mesa Boogie .50 Caliber+ and removed that socket when I replaced my power transformer. I don't understand who decided at Mesa's to install that kind of sockets on high voltage wires? You can get 670 AC Volts on the red wires that go to the rectifier bridge, so I decided to solder them directly to the board. I also replaced those cheap and poor 1N4007 silicon diodes with four Schottkys CREE Silicon Carbide C4D02120A 1200V 2A. After that, my amp sounds more like if there would be a tube rectifier in there. I also replaced my Output transformer with a Mercury Magnetics as an improvement. I've been modded that amp for years to get my own sound and now I think it's there! Not so long ago I had sound loss issues and found that the Phase Inverter 100K resistor was not soldered properly. I also replaced the other plate resistor from 82K to 91K, because I think the "long tailed pair" of 100K and 82K is a big mistake. You should have there about 10% resistance value difference to get the closer possible inverted and non-inverted voltage gain, that goes from the Phase Inverter to the Power Tubes.

[@richardleerodgers5303]

either the audio transformer has a short on one half of the primary or one of those 2.2 meg grid resistors is changed in value

[@GeorgeChristofi]

As for taking in jobs and regretting them.... I have a casio pg guitar that won't trigger the synthesiser section on the ram card. the standard sounds are fine and it works as a guitar but getting it to talk to the memory card... Been almost a year and I still get headaches looking at the thing.

[@emolatur]

I don't do tube stuff so I could be WAY off here, but, given that tubes run at absurdly high voltages and speakers don't, I would expect the output transformer to step the voltage /down/... 9V into the primary /shouldn't/ give you enough voltage for a neon lamp on the secondary... wouldn't you want to pulse 9V into the secondary and look for HV on the primary? Again, I don't do tubes, so forgive me if I'm missing something huge.

[@DeadKoby]

I hope I don't get this mad tomorrow. My amp kit build starts tomorrow evening. You and I have different styles... You trust your instincts, whereas I trust my tools. (Neither is wrong)... When my Vox Night Train took a drop, and quit, I tested my tubes and walked the board for a good long while (getting annoyed)... I did find the ONE metal oxide fuse resistor that pooped out on it. Aaarg... That adventure is on my channel. Tubes and caps are ALWAYS the first suspects on amps.

[@philhardy18]

I feel your pain brad , ive got a mesa heartbreaker combo in the garage waiting to be repaired . Im finding it difficult to even make a start . Leads flying in to 4 sides of the board , they're really a nightmare to service if anything serious goes wrong

[@richardturk7162]

Great video Brad and I'm glad you posted the video.

[@TheGuitologist]

Thanks man.

[@adrianshingler9783]

Nice to see Mesa design with easy maintenance in mind 😆😆😆 hope my little F30 holds up, can do without this kind of stress. Saying that an old JTM622 of mine that I rebuilt with a new cooling fan attached(!) emitted that well known and depressing burning smell the other day. We should all just go back to tag or turret board assembly, build them ourselves. The only way forward. Do all the fancy stuff with pedals 👍❤️

[@RodVonLongrod]

After watching various amp repair channels work on Mesa amps it strikes me as funny how they can still hold their value on the used market.

[@RylonBlackbeak]

You’re doing gawd’s work, homie... it’s not just for the customer and the helpful KZbin videos for generations to come... you also have to consider you are saving so many beautiful vintage amps... it’s win win win

[@mrjonradford]

I know your pain. Have worked on a few Mesa Boogie amps recently and it is not fun!

[@jloewenheim]

Great digging into such a frustrating problem and I hope you are correct on this, but I'm a bit concerned about the transformer test. Based on inductance theory, that battery test needs the transformer to be out of circuit to work. The clicking you hear in the speaker when you do it is taking the place of the light bulb flashing.I think if you hook up a speaker to that bench transformer, you will also see that the light doesn't flash but a pop will be heard through the speaker. Good luck on this, looking forward to learning more!

[@RafelioPsi]

Man, this is grabbing me more than a thriller movie! can’t wait to see how it’s gonna finish 🍿

[@garystevens6831]

6:30 - Cue the Inspector Dreyfuss whimper as Brad deals with the Inspector Cluseau of guitar amps...

[@garysellars8914]

Send it for landfill!! Honestly a dental visit would be better than having to do this! Whole design is way too busy and complicated making it a friggin' nightmare to work on.

[@222yep]

this one of your best yet. I was laughing out loud!!!

[@springy-2112]

the only stuff i know about amps is what you have shown..I think you are honest and humble to put this job on the web for the scrutaneers to jump on..peace and love brother.☮❤👍

[@TheGuitologist]

Every tech goes through this shit, no matter how sterile and clinical they try to make their videos through magical editing. That's no fun, and it's a lie.

[@springy-2112]

@@TheGuitologist thats why you're great to watch...i don't understand half the stuff but i used to understand none !! so it must work and as a user of valve amps its good to have an idea if things are not quite happy, ie overheating red plating noise oscillation etc etc.. and changing subjects slightly i just noticed im not subscribed any more !! fixed of course...this happens quite often ..channels im subbrd to for years suddenly unsub ..on their own, probably aliens or the FBI ...lol... any how thanks again keep being you ...cheers !!👍☮❤🤘🏻

[@rickluke1747]

For my mesa studio preamp exist no readable scematic. And the available is not correct... but the amp has a great sound with pedals. You can also not come under the board...

[@黒人-m3w]

I have owned several Mesa Boogies . And have had problems with all of them . And Amp techs have told me they can be a Nightmare to diagnose and repair.

[@pXnEmerica]

Lots of pops and clicks instead of a flash when touching the Mesa , interference with the camera?

[@Superjet113]

He said he had it plugged into his speaker and maybe thats what we were hearing..

[@pXnEmerica]

@@Superjet113 My understanding was the speaker output was connected to the neon with a drop, in place of the speaker. I was think more of the camera being close to an inductor that just changed. or from the man himself. "No. The popping was from my power supply being plugged into the same socket as my audio mixer. Spiked when the current rippled."

[@DavidImrie]

Would it not be a good idea to remove the transformer and test it on the bench?

[@lroy730]

Mesa Boogie Repair is 4D Chess in a 2D Bag . Or Schrodinger's Cat in a Tiny Tiny Box !

[@jeddak]

this thing is stuffed like a turkey

[@IPushHard]

When I saw the title of this video I KNEW what I was gonna see on your work bench. Another good laugh at your expense. Sorry bout that! : )

[@jimhart4158]

Check the grid leak, or change the tubes. Grid leak goes up with heat, and can cause thermal run away - the more it heats, the more it leaks, the more it heats, and so on.

[@nerfnerfification]

You would seriously wonder at the mentality of some of the amp design layouts - do they think the item will never need servicing? Marshall solid state stuff can be pretty bad and I've just fixed one that a 'reputable' repairman simply could not be bothered getting the board out - instead he clipped all the transistors off and resoldered them after testing on the board component side. This of course did wonders for the modern transistors!!

[@rguitar78]

"I'm going to have to call the guy that owns this thing and tell him" ...to find a new hobby. Wow, this repair would certainly put me off ever opening a Mesa amp again too. That rabbit hole runs deep my friend.

[@williammclemore5815]

Since it seams that the transformer was bad and causing all of the other problems, checking that might become a first step. In that way one would be eliminating an expensive part if it is good or eliminating a lot of time perhaps wasted chasing after ghosts.

[@MrGTO-ze7vb]

Did Mesa cut corners and install sub standard parts??? Hello Mercury Magnetics.. I need this output transformer

[@TheGuitologist]

Tiny OT with tubes running at super high plate currents for 20+ years killed it, I think.

[@NotMarkKnopfler]

My guess would be internal oscillation. Need to get a scope on that bad boy when it runs away. I'm not familiar with Mesa Boogies (though I like how they sound!) but I'd be looking at the negative feedback circuit. I wonder if a bad cap is letting DC in. Keep at it dude. (you may have already fixed it - I don't know as I'm posting this while watching. On the shitter, as it happens, where all my best thinking takes place!).

[@kristopher6031]

Runnin Runnin and Runnin Runnin

[@insanerotta5332]

I'm starting to think this amp should have come with a manual that says, "This amps in not designed to be serviced anyone or anything. I wonder how that board was even fitted into the chassis in the first place.

[@russellhltn1396]

Re-watching all 3 videos. I think you've covered everything component-wise. As for the voltage measurements when it was running away, you were losing bias much faster than screen or plate voltage. Bias -10.5, Plate 402, Screen 318, Bias -8.4 and falling fast. Of those, only the bias was below spec. Plate and screen was above spec (probably due to lowered plate dissipation.) My guess: the board has become conductive. Either that, or the schematic isn't accurate and there's something else in the bias circuit. If it was the output transformer, I'd expect to see the plate voltage rise on the tubes that are overheating compared to the other pair.

[@russellhltn1396]

Although, it wouldn't hurt to verify that you're not exceeding the DC blocking cap's rated voltage. Especially since you lowered the dissipation of the finals, the B+ voltage has probably climbed for all stages.

[@davidholder4121]

What kind of neon bulb (volage)? Gonna try this on a marshall i got in my shop.

[@TheGuitologist]

Anything rated for 120/240VAC will do it easily. These are the same ones used in Fender style trems.

[@davidholder4121]

Thanks.

[@chrisphillips6865]

G'day. if these amps have an open loop bandwidth in the predriver section possible RF osc due to a bad polycap, typical value around 3N3.. and coupled to the base of a predriver transistor. Maybe up to 1MHZ so hard to spot without a good scope.

[@Sith4Lyfe]

Anyone have the name of the song/ band at about the 3:30 mark?

[@halbertking2683]

Life's too short to work on Mesas.

[@antares4975]

Whats the name of the song at ~2:30?

[@j_freed]

Hey Brad, would you recommend doing a component upgrade on an '80s Champ 12 (Riviera design) since those ideas are given online, or should I just sell off the thing as the brittle-overdrive / weirdly-EQ'd little amp that it is? I'm intrigued and don't mind risking the unit, but don't want to harm myself or excessively trouble my kindly electronics-engineer friends. Thanks if you can point me in a good direction. And appreciate all you do here too.

[@thatguy9211-q8o]

Cuss word count:.........'Personal Best'!! Great video.

[@hearpalhere]

Crazy stuff Brad! It does look like a nightmare indeed. Good luck, hope the output transformer will do the trick.

[@jimhough6233]

You are way more patient than I am. By that second time I would have given the dude a refund. But that means defeat. Mesa mesa.!

[@poot111111]

First of all I know nothing, with that out of the way I was surprised to hear him still able to play if the output transformer was bad. And didn't the client play it at gig volumes until it ran away to red-plate? How is this possible?

[@enidsnarb]

This was my experience working on EL84 Mesa Boogie Amps , very unfriendly when it comes to repair!!!