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Nice channel, just subscribed.

Had the same with an Orange OR200 amp. Worked fine up to half power then major distortion. Replaced output tranformer at a huge cost but it is a 200w amp and no problems.

Interesting, especially as these amplifiers are considered to be one of the reference amplifiers of their day but the gentleman seems a little unfamiliar with them.. Incidentally it was 10.605 squared....Keith Snook supplies a modern replacement for C4 and C6 in an identical housing to the original....

Funnily enough I diagnosed the exact same problem in my HT5R Combo last week. I'm not paying £75 for their crappy OT though! The Hammond 125B is a direct replacement if I'm not mistaken.

Interesting OT failure.

Every SMT component amp chassis is a foundation for a point to point all tube circuit. Install a power amp resistor on the output jack to prevent a no load scenario. Great work sir!! You made this amp alive again!! :)

Blackstar has a terrible reputation. So many amp techs refuse to service them

You can try aluminium foil dipped in water on rusted chrome, rub away. The bicycle lot use it for their vintage bikes. Of course it won't bring back the chrome plating but it does improve the appearance.

Thank you Stuart.This tutorial worked for me.From silent to sound.

Crikey, it's just an amp. 1968 colour TV's had less components than that thing.

Actually I do have one of those. Actually mine has two sockets. Anyway my question to everyone I run across. I have a blues junior. It hums fairly loud when warmed up. With the back still on, If I put my hand, or a couple of fingers, between the driver tube and power tube, it stops. Any idea what this indicates is the problem. I'm guessing a capacitor/capacitance issue of some sort, but haven't figured out a solution. Maybe a ground issue? Thanks in advance for any ideas.

I ask this everywhere I can. I have a blues junior. It hums when warmed up. If I put my hand in between the driver tube and power tube it goes away. Sometimes completely, if I hold it in just the right spot. Any ideas as to what this indicates?

Nice work Stuart...Bit of a pig those Blackstar amps..😮..😅..Ed..uk

As always, your videos are very helpful and encouraging!

Stuart, It's always exciting to see new content from you. I think the fact that you show the process you use and explain the issues simply is why so many people watch you. I know I've learned a lot watching your channel. This was interesting, but I don't know if I would have clipped a new transformer like you did. However, I'm a novice and voltages scare me. Always informative and entertaining. Thanks, Mike

Nice!! I have an amp with the same problem. Do you have a shop? Can i send you mine?

Great job! I’ve heard that Blackstar does not provide schematics, is that true?

Consumer electronics mentality. They knew when they made these that they were destined for the landfill in 10 years or so but hey, you can't sell as many new amps if your old ones last too long and are readily available on the used market. People love to bash Mesa for lack of repairability, but smt components are the mark of a true sociopath imo.

To remove the FET's without damaging the pads, just clip the leads off and then de-solder each lead and pull it out. It'll save you de-laminating the through hole pads and possibly damaging the barrel. By the way, I learn much from your channel, thanks!

Just had a Blues Junior doing the same . I also didn't at first think it would be the OT transformer .

Those FETS that you replaced do what to the phase splitter section?

Pretty peculiar little amp, because if I have understood correctly, the triodes of that 12BH7 work as a push pull output stage. Those around 450V plate voltages seem quite high but those tubes have been widely used as oscilloscope deflection tubes at those voltages, and often been tortured at max plate dissipation as well. Possible no load situation could have killed that OT. Very nice that you could fix it. 👍 The output power of that high voltage beast could be even 3-4 watts, I guess. 😂 That kind of output stage could make quite a nice reverb driver when using 8 ohm reverb tank.

Marshall doesn't have boards for a dsl 40 c anymore . Unless u may know where I can get one I'm out of luck .

Good tip about marking the bad part. Even though I've never once ever took a bad part off then put it back on thinking it was the new part causing me hours more diagnostic time, I mark the old part with a paint marker pen- red for bad and yellow for maybe still good.

I really enjoy watching your videos - Thank you !!

Excellent diagnosis and repair Stuart.. About five years ago I had the same thing happen to my FBJ .. All the readings on the output TX looked okay.. But I had another TX kicking around so I thought there's nothing to loose and I connected it up. Hey presto it worked perfectly. I still have the faulty TX but can't figure out to this day what's actually wrong with it, but there's something going on for sure. I'm pleased to say I'm one of your 'million' as I've been with you from the start of your YT channel. Congratulations and well deserved.

At 11:25, the whopping 462 volts B+ measured at the 12BH7 was probably a clue, because it appears the tube is idling at virtually no current, which indicates an incorrect load, due in this case to the bad output transformer. It would have been instructive to measure the B+ after the transformer was replaced; I would bet that it dropped by at least 20 or 30 volts. As for the blown output transformer, your megger might have shown internal leakage or capacitive coupling. PS, 75 pounds for a puny transformer like this is highway robbery! You could probably have looked at a tube manual and figured out an appropriate impedance match so that you could replace the original transformer with a Hammond or something else for half that price, or measure the turns ratio of the brand new transformer before installation so that you can find a more reasonably priced substitute if you ever need to replace one again. You'd be doing a service for other Blackstar owners and their long-suffering technicians!

Well done Stuart, same with me I don't like surface mount . Great result

Poke holes in the solderwick with an awl or tiny jeweler's screwdriver and then you can place the wick directly over the stub of each component lead. Adding the special low-temperature solder known as ChipQuick is also helpful; it stays liquid for almost 10 seconds without further heat being applied (ChipQuick is also very helpful for removing SMD parts with multiple pins). PS, I'd recommend adding heatsinks to those Mosfets; the discoloration of the board indicates that both the mosfets and the resistors are generating heat. Unfortunately you can't heatsink the resistors, nor easily fit larger ones, but replacements could be mounted a little above the board for better air flow.....

Quite a poser, this little unit. I'm impressed by your perseverance in deducing the issue. Enjoy your weekend, Stuart. Cheers!

What a crazy way to build a simple amp and then you get robbed for the OT. 😡

More good work Stuart.

I'm still planning to drop off my jcm900 to you, keep watching your videos and founding them very interesting. Thank you

This video was exactly what I was looking for AND an example of a 'great' Ebay tutorial. What made it work for me was a simple schematic and the application of Ohm's Law, you know, old school stuff - Thanks!

Just FYI for the Origin series: for the fx loop to work, a TRS plug needs to be inserted into the foot switch jack with the ring open. Ring to ground turns the fx loop off and tip to ground turns the gain boost off.

I wouldn't get to hung up with the carbon track but does mineral spirit effect the plastic ? Especially old plastic ?

super useful thank you so much!!!!

My ac30c2 is different

What kind of soldering iron do you use? I have an Ersa station with 60 watts, it never gets as hot as yours. Best regards Martín

what is all that "buzzing"?!?? first thing I do when an amp comes in the door is test ALL of the tubes!

Up until a few years ago I had a pair of Quad II's. The serial numbers on my pair were reasonably close, certainly not consecutive. The component layout and wiring loom is of excellent quality. I did intend to restore them but in the end I sold them on at a modest profit. They were never intended as being on display or a visual feature, more hidden away in something like a Heals cabinet. The leaky caps are hardly a surprise given the age. I once restored a valve radio and replaced all the electrolytics and every waxy cap that was in it. Must have been 10 or 12 waxy caps. They were all very leaky. I think your little board and main smoothing caps was the right idea. It's probably possible to cut open that capacitor can with a dremel wheel and hide new caps inside but it's quite a bit of work. As you stated, your board is easily reversible should someone wish to do so sometime in the future.

Hi Stuart, i have a question related to this exact amp, i've got this amp about a year ago and it is fantastic, i use it on studio, i take good care of it. The other day i was using this amp when i noticed that the clean channel was not loud enough, i turned the volume knob to the max and still had the same issue, and the sound was also not clear enough. The dirt channel sounded perfectly, no issues at all. could this be related to the valves? if i find a valve that could be broken, can i just change for a good one instead of buying all of them? thank you so much!

I'm late to the party. Having established that the hum was being picked up by the volume wiper (grid) I would have separated out the shielded cable from the bundle, and moved that around on its own. It looks like you left them bundled the whole time, since the yellow bands look untouched?

3 decades ago I went through my crazy Hi Fi phase. Having built an EL84 PP amp it wasn't long before I was replacing the resistors with 'better sounding' replacement types. Of course the capacitors were the next on the list for replacement. Then I heard that a 6V6 sounded better than an EL84 so I converted it to 6V6 PP. Most of my original build was cobbled together from parts that I already had including the output transformers. It even had a choke power supply. It's all too easy to convince yourself that any change you make must be an improvement. The changes that I made to my amplifier was extra experience but that's about it. I don't think any of the changes improved the sound one bit. It got converted back to EL84's because I could see the heater glows much better!

Nice one Stuart - helped me fix the exact same problem on one of my customers amps - And yes…love to see all the natural mistakes, helps me avoid doing them🤘😅

Wow, indeed Sruart: 'hope you learned something...' = yes, every time, thank you! Your generous sharing of your experience is more than appreciated!

Brilliant, thanks for your effort. Be careful with just pure alcohol on pots as it has zero lubricants which "could" lead to more wear between the wiper and the carbon track. (Maybe another video for you, 😁). As you noticed when DeOxit dries it does leave a little film of lubricant behind. Of course their Fader product includes a higher percentage of lubricant for high use faders.

This amp is on "evil-bay" right now for the bargain starting price of £4995.00,,,,,,,,,,,,,,,,,,,,,I'm not sure if the Seller will accept kidneys?.

Excellent. I've been struggling to find out what goes on in these things for about 45 years! Really interesting! Many thanks!

The white material left on the top may be removed with Goo Gone and then the vinyl wiped down with Armor All.