Happy to see you post again Stuart. These amps do look quite complicated. I have begun to use number tape when removing many wires at a time. I also take many pictures and draw a diagram as I have seen you do. I'm getting better at this and am enjoying it as a hobby. Thanks again for sharing your expertise. Mike
I wondered where you'd gone, Stuart 😊 Good to see you back. Always check the 16 Ohm socket, it switches the other two sockets off if something is plugged into with if them to avoid someone plugging another cab in, causing an impedance mismatch and seeing the output transformer off. If the amp had been used at 8 or 4 Ohms for a few years, the 16 Ohm socket will burn up and present an open circuit, causing a flashover, blown cathode resistor, burned valve socket or worse... ALWAYS CHANGE THEM with every service !!! The other common problem is poor valve selection. The DSL & TSL's have very high HT and a lot of valves can't deal with it. I've seen several that have come in fitted with JJ's and the Bias is running away, not because the board is faulty, but because the valves are crap and can't handle the voltage. Shove a decent set of valves in there and the amp will settle down beautifully. Personally I'd have changed the output valves, but I guess it's 'horses for causes'. It certainly looks like it's had something spilled through the top. I don't think I've ever seen a chassis looking quite so distressed 😂 FYI: The factory Bias setting is 90mV per side using the connector on the rear of the chassis, but personally, I usually set them for 80mV. 45mA per valve, what were they thinking 🤔 Mind you, with such high HT I guess everything else goes up with it... Valves are a lot like incandescent light bulbs, they can last fifty odd years or they can blow up straight out of the box and they can certainly have intermittent shorts. I've got an old saying 'Just because it's new, don't mean it's any good' - and that certainly goes for valves 😂 Anyway, I look forward to the next 'terribly designed' amp you work on and all the best, Stuart. Squidgy squeeze
Hi thanks for the response. I didn;t know that about the 16ohm socket, that's a really good tip. Yes I did know about the valves after suffering a lot of blown JJ EL34s. The JJs just can't take the plate voltage. I use Marshall EL34s which I think are EL34B. Also jj EL34II are ok. Thanks again for your very useful and knowledgeable contribution.
@@stuartukguitarampguy5830 The sockets are a quid each and it's just not worth wasting the time. In the bin with the old one and in with a new one. I see it all the time, in fact I'm doing one right now 😂 Take care Stu
I advise jumpering the ground shunt contacts on the 16 Ohm jack. There's no reason to break that connection when plugged into the 16 Ohm jack and I consider it a PCB layout error.
That was tricky Stuart !! .. It always worries me when I see a 'blown' component and there's no hard & fast clue as to what caused it to blow. (apart from valves of course who operate by their own set of rules 😅.... Great video and nice to see you back on again ..
Thanks Pete yes I also like to find out exactly what went wrong. I don't like mysteries. I think I did this one a few months ago now and it hasn;t come back!
I'm glad to see this latest post, Stuart. You were absent long enough to cause concern. This was quite an enigmatic amp to be sure. I too detest the DSL, and TSL series because of the ever-present reliability flaws. Coincidently, I am curious about how parts availability will be effected by the Swedish purchase of Marshall. Have you experienced any change in the parts matrix? Enjoy what's left of the weekend, and remain in abundant health. Cheers!
Hello Stuart, good to see you back. Did you ever get to the bottom of what had been spilt inside? Maybe some conductivity on the valve pins on the end valve but when you removed it, it cleared the fault? Mending those things is never fun. Another great video. Good to see you back online. Take care.
Would u know where a person might purchase a replacement board for a dsl 40 C . If i knew then i would not have bought it . Appreciate ur channel . Iv learned alot . Thks
For a couple of sections of this video you had no speakers plugged in or a dummy load? One issue I have with DSL/TSLs is the solder underneath the mains fuse and HT fuse holders. It is worth taking out the small board with the IEC mains connector on and checking the solder. TSL amps are trash, terrible.
Hi Ok thanks for the tip on the small board. Did you see the earlier post about the 16ohm socket? That was useful too. I only plug in a speaker or dummy load if I am going to put a signal through the amp. It's not needed otherwise.
Good job. It looks like it was just a faulty resistor. I have two Marshall TSL60s. I think the DSL and TSL series sound good when they're working. Personally I think they made them too complicated. Too many channels, too many knobs, too many features and too many switches. I believe they were competing with Mesa when these were designed. I play my TSL60s through the lead channel 99% of the time.
YEs I really don;t like the TSL and DSL, there are over 150 interboard connection points, any one of which can cause an issue. No idea what they were thinking designing it like that.
I thought the DSL and TSL were notorious for the bias drift problem which generally requires a bypass and a new bias PCB replace. A bias drift would have exhibited as a runaway plate current and burnt cathode resistor makes sense. There are after market boards and instructions for it.
Hi Yes that's a common problem but only in earlier issue boards. I think this one had a late issue, either that or I had changed the board on a previous visit, I can;t recall.
Hi. A longish answer to this. Firstly, when I revalve for a customer I just buy in a matched pair/quad or whatever so that solves the problem. I don't have the in house equipment to test transconductance (basically gain) of power valves but I also don't believe it's that important. Here's why. The gain of a power valve is actually quite low (compared with a preamp valve) and so any small difference in gain doesn't have THAT much effect on the overall signal. And in any case, the effect it DOES have would result in a very small amount of distortion on the signal. What??? Distortion in a valve guitar amp?? We wouldn't want that now would we! The only time it might matter would be in a HiFi amp but even then, cynic that I am, I wonder why the **** anyone would want a valve amp for HiFi? Back in the day we were chasing 0.001% total harmonic distortion for our HiFi amps. A valve HiFi amp would have something like 1% distortion! So why do HiFi buffs go for valve amps? I believe the answer is they like the distortion. They perceive it as 'warm'. So it's exactly the same reason as guitarists prefer valve amps - they don't like the clinical, clean sound of a transistor amp, they like the distorted 'warm' sound. just my view of course!
@@stuartukguitarampguy5830 If you measure AC voltage on the grids of the power tubes and measure the AC voltage on the plates of the power tubes this is Vout/Vin= GAIN but you have to convert it to Gm transconductance how so?
Well Done. Personally, I could not sleep till Id removed all the boards, but the cost would have been completely unreasonable for the customer. Viewers and customers don't understand the commercial reality of such repairs. I suspect that the spill ran through to the bottom of the new board you installed and caused an short. But the time it takes to do that is well beyond the fee the customer would pay for. Chances are that the liquid has dried out and wont cause the issue again anyway. But it could be corrosive and worsen. who knows! Its always a trade-off when we repair a product that is price sensitive for repair as to how far we go to be sure we got it nailed. I bet you didnt charge for all the time you invested. Anyway, this is the commercial reality!
I never like it when I can't find the root cause of a component failure, Perhaps it was a faulty resistor? It's possible that of the 30 million they make every year, that was a bad one from the factory and it just gave up after a few hours of use. As they say "time will tell". ;)
Yes agreed, I hate not knowing why an amp failed. The other one I get all the time is "The amp failed on a gig, no sound at all." Comes in to me, endless soak testing, banging, waggling...nada, amp is totally solid.
