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One wire on the left across the 16-ohm jack ground contacts, and three at the right across the impedance selector terminals.
For what it's worth one of my jobs today is a DSL100 which belongs to a local rehearsal studio. It's died several times in the past, and I've not only done this to it but every other normal upgrade I do, and it's also running at 50W (having fried the main PCB around two of the valve sockets, I thought it easiest to simply remove them) so the power section should be under less stress. (The OT is running at the correct impedance, I swapped the taps.) To be fair, I haven't seen it for a couple of years.
But even given all that, it's *still* blown the OT...
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
One of today's repairs is a DSL100 with a badly burned PCB - it's a recent issue too, not one of the originals - and four blown power valves. Given the state of the valves it looks like the HT has got into the bias supply - a couple of the valves have started to literally melt. Even assuming there's no other damage, this is a £250+ repair. The new board and power valves alone come to about £170, and that's before labour and shop margin. Given that I would have to guarantee it I would want to do all the other known upgrades as well, which would add probably another £50. And that's even if it hasn't done anything more drastic like fried one of the transformers, which is quite possible.
On that basis the owner has refused the repair estimate, which I entirely agree with. If it needs repeating, just avoid these amps unless you want to risk this sort of trouble and cost.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The HT is already quite high in these amps (usually around 500 VDC in our workshop), and this would creep up with only 2 out of 4 valves.
Regardless, I never understand why "cheap" amps use such high voltages, as say using 450 VDC would result in only a bit less volume but much better valve life and reliability.
The real problem with the design isn't the static HT, it's the huge voltage spikes developed between the plate and screen of the last power valve - where they fitted that cap to suppress it, which is a clear 'band aid' solution. Even with a 1KV-rated cap, as I'm sure you've seen too the cap sometimes fails. What voltage is being produced here?!
Of course this was one of the valves I removed, since the board had arced through here as well as frying the cap. The other one is the second one on the other side, which is also where the board tends to arc most often - and has done on this latest dead one as well, even with a later revision board.
Something is deeply wrong with the stability of the circuit and/or layout for it to do this.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Wizard
Freidman
etc
They exist for a reason.
http://www.lynx.net/~jc/TSL122.html
The pic is this one, which is very similar to what I found today -
http://www.lynx.net/~jc/lwMarshall1.jpg
- but what's much more damning is the sheer number of design and manufacturing faults listed here - some are a bit technical, for the non-expert... but the point is that the designers at Marshall should be experts. It staggers me that a company with their apparent experience could have put so many serious mistakes into what should have been a flagship product.
They're just an appalling piece of junk, and in my opinion it's really not worth throwing good money after bad on them.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Oddly the TSL60 is not a 2-valve version of the TSL100 but a different design more similar to the DSL401/201, which doesn't seem quite as bad for this type of failure, although the amp is slightly less well-built overall.
The least bad of the series are the DSL401s, which although not fault-free either are actually easier to make fairly reliable - they don't seem to suffer from the same serious board failures. The DSL201 has very poor transformers, especially the OT.
Even more surprisingly given what you would expect from the usual reputation of 'outsourcing to the far east', the new Vietnamese-made DSLs seem to be far more reliable, so far at least. I haven't yet seen a single one with any fault other than a blown valve.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I take on board ICBM's misgivings and perhaps a Jet City is in my future but I'm perfectly happy at the moment, and I can live with the possibly imminent demise I hope it's not imminent though, I would struggle to get this sound again
hes just selling his Jet City and gone to a Helix, so I'll have to wait 18 months for him to sell the Helix and return to Jet City again.
In addition to the extensive list of design cock up you've listed, I've also seen a few TSLs where a couple of film caps in the pre amp (from memory these are DC blocking caps for the DI out; irony a feature that is probably NEVER used) have gone leaky and this has dragged down the bias too.
The caps are rated for 63V, but if the HT is energized before the valve are conducting, then then these can see a higher voltage.
Again another very poor piece of design.