Nate Dort wrote:DONE!Hubba hubba!That's a slick bit of woodworking

Thanks for sharing that, Nate. I've got a 441 ”technically a 541 Black Fire model ”that not only has a rattly capsule, but is lacking in low end. I got it for free so I wasn't too heartbroken, but it's good to see that this might not be the end of it.

Nate Dort wrote:Borked sennheiser 441 on the way. Something apparently rattling inside. Guess I get to perform some surgery on one of these for the first time.Got it yesterday. It passed audio, but was quiet and thin sounding. No lows.Opened it up and the capsule assembly was rattling around inside. The plastic had broken at the thinnest part, near where it threads into the silver tube that houses the transformer/filter PCB. I've seen stories of broken PCBs in these things, so it opened the silver tube and didn't see anything suspect in there. Then I hooked the capsule directly to an XLR and plugged it in to a preamp. Still thin sounding. I bumped the plastic horn thing in front of the capsule and it sounded good for a second. Tugged it a bit more and that seemed to fix the low output and thinness. Apparently that plastic horn assembly was slightly touching the capsule and damping the movement.I epoxied the broken piece of the capsule assembly back on and reassembled. Sounds good now.

Mason wrote:Thanks for sharing that, Nate.X 2. I had a 441 years ago that had the same kind of symptoms you describe, but I just got rid of it rather than mess about. If I'd had your guidance I might have taken a shot.

EDITED

Nate Dort wrote:The fault detection in this thing is somewhat complicated. It's supposed to detect the current through each of the 10 ohm cathode resistors on the power tubes. I measured two of these resistors at about 7 ohms, so they're out of spec.Turns out these resistors weren't bad after all. There were two shorted diodes connected to them, which was skewing my in-circuit measurements of those two resistors. As soon as I lifted them, they read 10 ohms, which got me probing everything around them.The third diode on the bottom-left was also shorted, which explains why the amp was going into fault mode as soon as power was applied. Normally, a fault should only be detected after coming out of standby, as the HT lines need to be active for the fault circuitry to detect bias issues.So, the fault issue is fixed and it comes out of standby now. I didn't get a chance to run any audio through it or bias it properly, but the bias LEDs do turn on now and respond to changes on the bias pots. I'll need to see how they correspond to actual measurements across the cathode resistors.

Nate Dort wrote:I bought this broken Mark Bass Combo Head II for next-to-nothing. Turns on apparently, but doesn't pass audio. At the very least I'll pull the amp and have a cheap 12" cabinet. Should be able to get it working though. I design Class D amplfiers at my day job, so this shouldn't be too difficult to figure out.This arrived yesterday. I was wrong about the failure mode of this one. The description on reverb was unclear, as dude was selling two of these, both broken, and apparently copied portions of the text from the other listing. It turned on, intermittently, and would randomly shut off, but it did pass audio. I opened it up and started poking around the power switch. I think the terminals were oxidized or loose or the switch had dirty contacts inside. Pulling the wires and spraying contact cleaner inside the switch solved the problem. Not bad for $80 shipped and about 30 minutes of effort. I'll probably keep this for a while, as I don't currently have a little bass combo and I could see it being useful.

Second SVT 2 Pro showed up with shipping damage. The output transformer was loose and dented the top cover and smashed a preamp tube. One of the front handles was loose and bent and rubbed against the front panel.I don t want to return it, because I know I can still fix it, but I m going to push for a partial refund.Otherwise, this thing is in great shape. It s actually a couple years older than the other one, despite being in much better condition. Tubes are original from '92, so I m guessing this has been non functional and in storage for a long time. My biggest worry at this point is that the output transformer is blown, and that s why it was put in storage in the first place. A replacement is about $300.

Got the first SVT up and running. Sounds like an SVT. I've never owned one of these and only played through one once a long time ago, so it was a revelation when I fired it up and heard THAT sound.Replaced the broken line-out pot on the back and cleaned/lubed the scratchy master volume pot.I pulled the remaining tubes from the damaged SVT. They all test fine. The 6650s are actually 6550A's, made at the GE/MPD factory in Owensboro, KY (the old KenRad plant). They all have a date code of 92-47, which makes them some of the last ones to come off that line, as it apparently shut down in June, 1993. Kinda strange, as my wife's family is from Owensboro.The rest of the tubes are all Sovteks or Chinese SLM "Hot Rods" from 1992, so nothing special there. Pretty sure they came stock with the amp.I've read stories of the tube retainers on these things digging into the glass, so I got some small-diameter high-temp silicone tubing and sliced it to act as padding.Still haven't heard anything about the shipping claim. Nobody has followed-up to do an investigation or anything. I'm guessing they might want to look at the box and packing materials. I'd like to get this settled so I can properly tear into the second amp.

Reverb wanted me to take a bunch of photos of the box and packing material, and then they were going to arrange to return the item to them (not the seller). I always suspected that s where they got all their broken items that they sell under their œReverb Garage Sale account.I told them I wasn t interested in shipping it back and that it wouldn t survive another trip without significant damage. They credited me $100.