Hello all, About a year ago I bought a used DSL401 combo. I read prior to buying that amplifiers made mid 2003-after had corrections done to the board/bridge rectifier in reference to overheating. Here’s my question. My amp is built mid 2004, yet when I yanked my chassis out to look around at where the bias pot and test point was to potentially change my own power tubes, I noticed the board is marked DL-40-60-00, and if I’m reading right, the updated board should be DL-40-60-02. Shouldn’t my board be an 02? I’ll add photos if I can.
The pcb wouldn't have been any different post 2003, just a couple of different R values. The check is, when you adjust bias on it, does it sweep from around 800mv down to very little?, (ie post 2003 values), or is the lowest it goes around 900mV to 1000mV?(pre 2003 values)
Hi! I’ve seen your 401 mod thread, you’re EXACTLTY who I’d hoped would respond! I don’t yet have a meter, but plan to get one soon, obviously I’d get it before I attempted a bias. The reason I ask about the pcb number is an email I got from Marshall today... when I asked what changed were made post 2003 this is what they sent : Hello, Thanks for contacting us. These are the changes that were made DL40-60-02 CIRCUIT DIAGRAM. R31 WAS 9K1 NOW 2K7 R36 WAS 10K NOW 3K3 C75 WAS 10n NOW 2n2. KEVIN DRURY MARSHALL SALES AND SERVICE SUPPORT 1649 BARCLAY BLVD. BUFFALO GROVE IL 60089 All internal electrical work must be performed by an authorized Marshall service center I’ve also seen a circuit diagram with that number on it as well. My 401 is my first valve amp, and it gets pretty warm, so one of the things I wanted to peek at were signs of any heat damage, which I found none whatsoever. I changed the preamp tubes out myself back in December. They were original (said Marshall on them). Power tubes however are JJ, leads me to believe they’ve been changed at some point.
Any other ideas?? Does anyone maybe have a post 2004 model with a photo of their PCB showing “02” instead of “00”?
Well I found a picture inside mine. I bought it in 2006 and its a 2005 model, definitely with the cooler bias circuit.... .....the board is labelled as DL-40-60-00, like yours.
Awesome, thank you! That’s exactly what I was looking for. These power valves are still working great, so I don’t have any reason to change them out just yet, but I want to be able to do this myself when it’s time.
Found this too. Looked through the pictures I took of the board for any of these parts and found R36 in the corner. Values match.
Hey @JohnH Just wanted to let you know that I ended up getting a multimeter today and alligator clips. I didn’t change the power tubes, but I removed the chassis and adjusted the bias. It was set to .410 mv, way too cold. I set it to .750mv to start... I’m waiting for it to cool down some, then I’ll take it for a spin and see how it sounds. Edit.... I actually lowered it down to .650mv. Sounded good at .750 but got very hot. Going to try .650 for awhile and see how it does.
Sounds pretty good at .650mv. As I mentioned I didn’t change out the power tubes, but I may. I bought the amp last October, and the guy couldn’t tell me when the tubes had been changed. Couldn’t tell me how long he had it and said he got it in a store where it sat for awhile, but was pretty sure he’d bought it new. Preamp tubes were Marshall labeled, and I changed them last December. The power tubes are all JJ brand EL84. I have no idea how old they are, but I do know I’ve easily used the amp for at least an hour a day since then. The tubes all look ok, no red plating or weird noises. I’m inclined to just change them out for the sake of having a fresh matched set.
The serial number is at top right at the back. Mine says M-2005-32.. xxx. So it was made in week 32 of 2005
