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dead bug psu


voodoochile

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I finally stopped dicking around with psud and actually dead bugged this psu I've been mulling over. It's alive, and no parts were killed. Glad we don't have a cat anymore.

ear2psu_board1.JPG

Loaded it down, and it was pretty close to what psud predicted. Not knowing what the regulation of the transformer was, I adjusted the setting in psud until it matched the output, and it scales properly. Added a small resistor up front to bring the output down a bit, and I think I'm done.

No electrolytics, with a shared C-L-C, then it splits into two channels, each having an L-C-R-C string. The output power tap is at the L-C jct, the gain stage tap is at the end. Rectifier is a 5V4GA I had on hand.

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Great work as usual Mark, can't wait to see the amp you've got cooked up. :indra:

Meh, it's not going to be uber-sexy or menacing, but it should sound good at least. ;) If the amp goes as as well as the PSU did, it ought to be pretty sweet.

Economic stimulus by gear lust. It isn't bad, its...patriotic.

Absolutely. Both those meters, and my 45, were made in USA.

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Is that tape wrapped around one of the capacitors?

At last, I don't feel alone anymore! :D

Guilty. The cap is fastened down, and I didn't want the choke to slide into something uninsulated. OSHA loves this project so far!

I don't see the obligatory ground wire to the wood chassis :D

I couldn't find a wood screw to fit a star washer, so I floated it. :D

And you desk is way to clean.

A clean desk is a sign of a dirty mind.

Oh come on... Nate must have told you how bad it USED to be. Let me back up a little bit...

themess.jpg

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do you solder standing up?

Occasionally. You can see the edge of the barstool to the right. I was using it as a temporary table near the tablesaw, which is where I was doing a bunch of layout and markup of a chassis.

I would have done this on the workbench if it wasn't so cluttered already. Or neat, if you ask Kevin. ;)

The blue chunks of iron on the right hand end are a jointer I'm still in process of doing over. Still looking for bearings... Walker-Turner used some odd lot for that model. I do have about 5 projects going, but only three are on the bench. I should have some legitimate progress to show by the end of the weekend.

Nate: You bought a big tool?

I have a co-worker who qualifies as a big tool- I'd have paid your mileage to take him away.

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Got some work done on a (temporary) chassis, made from an old scsi optical drive housing. Painted with some bronze hammerite, which is sort of like a warm shade of very dark gray, almost black. Tube box is for color reference.

scsi_layout.jpg

scsi_punched.jpg

scsi_painted.jpg

scsi_assembling.jpg

The smaller oil caps are a pretty baggy fit, but it's the closest size punch I had, and this is just for trying out some different configurations easily.

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Finished wiring last night right at 11pm. No smoke came out, voltages looked good enough initially, so I hooked it up to a source, and got sound! I was surprised, since I was pretty tired. Wondering if I had swapped the filaments and B+ or something.

scsi_built.jpg

Darker shot with power on:

scsi_running.jpg

Yes, I did end up going with an old 4-pin 80 rectifier, which I originally wanted to do. I thought the voltage would be too low with it, but after making some further adjustments, I was actually running too high with the 5V4-GA. I'm going to make some careful measurements tonight or tomorrow to see how close my currents are.

I suspect that the output tubes are running a little less current since the voltage is slightly higher, but I wanted to start a bit lower and work it up, so this is okay.

One foible is that the present cathode resistors on the output are only 3W. I thought I had some 5W, and I was wrong. Those little bastards are running extremely hot. I'm going to end up changing them anyway to tweak the operating point, and will be sure to get some 5-watters in there. I only ran it about 5 minutes at a time last night, sutting it off to let it cool a bit. No discoloration though. I'll know better once I really get in there with the meters. In my present amp I have 5w resistors in this location, and they are dissipating a little more than 3w... but the voltage is a good bit higher in this amp.

Before you ask, Nate, those load resistors did not actually smoke, but you can tell the amp is on with your eyes closed by the smell of the hot paint above them! :D The ground bus is like a radiator until I swap them out, you'd love it.

Fired up the cowboy junkies for a bit, then some gorillaz to see how it handles heavy bass, just for fun. I was exhausted, it was late, so of course it sounded "really good to me". Some subjective impressions will follow later on, after I get the loading where I want it, along with some better pictures.

Edited by voodoochile
typos
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:D It will be interesting once I see exactly where it's at. The tubes are capable of 5.5 watts at 550 volts. I'm not going that far, but it's running at about 50% higher voltage right now, and the bias is up there, too. I remember now why the voltage ended up higher than expected with the 80 rectifer- I had a dropper between the transformer and the 5V4-GA. I dropped the dropper when I decided to go ahead with the 80. It seems to demonstrate better transient response with either a dropper- or the higher loss of the 80. The 80 wins by virtue of having an st bottle. :) I have a gorgeous pair of Tung-Sol 80s, and they really arent fat enough for anything much nuttier than this little project, so I really wanted to use one here. Old school even as tubes go, but they are pretty.

I do have a half dozen 872-A rectifiers, but I need a filament ransformer the size of a lawnmower to run them. Bummer.

We need to set a date for some qualified listening soon. With appropriate bebidas, of course!

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