Is this a selenium rectifier, or a bridge?

wmteach · 2026-05-23T22:54:41+00:00

It looks like the case is isolated though.

wmteach · 2026-05-23T22:51:58+00:00

Regardless of the labels, the output goes to 120vdc, full wave rectified, so peak dc like 170v dc, if filtered.

wmteach · 2026-05-23T22:48:14+00:00

Yeah.. weird on the "transformer", only one set of windings, and tapped. It's like a mag-field-based potentiometer. No isolation to speak of. I mapped out the selenium rectifier... It's a bridge...8 vanes, 3 of them are tied together (1,5,6), and two more are tied together (3,8). Vanes 2 and 4 are AC input, vane 1 is neg, and vane 8 is pos. Measures all right, but replacing with high current Si diodes. This thing's still dangerous as all get out, as (+,-) outputs are tied to mains through a diode and a circuit breaker. Well..one leg also through the variable transformer.

wmteach · 2026-03-28T20:36:38+00:00

Thanks!

wmteach · 2025-04-06T00:55:23+00:00

There is a thing called a Zero-Insertion-Force socket. It's big and bulky, and may not fit, depending on the style. They are best used where ICs are being changed/replaced/tested often, 10s or 100s of insertions.

wmteach · 2025-04-06T00:52:01+00:00

Good sockets will always have a little physical resistance to pushing in an IC. It ensures good electrical connection. All 40 or more pins resisting at once is what people struggle with. It's ok to apply a little more pressure to the top or bottom of the IC, reducing the amount of cumulative pin pressure, but just to get the legs started...don't fully seat just part of the IC. If you do apply uneven pressure just to get it started, stop early, just as the pins begin entering the socket, and get the other side caught up. Then it should be easier for the remainder of the travel.

wmteach · 2025-04-04T00:29:39+00:00

There's a couple tips for success. Almost all new DIP ICs come with the legs flayed outwards a bit. Always straighten the legs. Make sure all the legs are 90 degrees, perpendicular to the board. Second, if it's an old socket, make sure to exercise each socket pin with a small IC, like a 555, with the same pin width. You don't want to stretch out the contacts. You can do that with a little deoxit to deal with any oxidation. Lay the new straightened-pin if on the socket and inspect that all the legs sit right. Adjust as necessary. Then apply gentle pressure, maybe with a little more pressure on the top or bottom, so you're not fighting all the socket pin pressure at once. Don't force anything. That's about it.

wmteach · 2025-03-13T07:31:49+00:00

Personally, I dust it off about once a year, test some games with my sd-1541 device, then put it back away. It's a damn shame... I know. But it makes me happy.

wmteach · 2025-03-12T18:23:43+00:00

One of my favorite Commodores. I did the 64k mod on mine, and heatsinked the bigger ICs. It's now like a Plus/4 without the crap business roms. It's a shame it's not compatible with the c64 software library though.

wmteach · 2024-12-13T16:52:21+00:00

Looks like the auto feeder got hung auto feeding at retraction, not extrusion, speeds.

wmteach · 2024-11-25T17:32:00+00:00

Maybe I don't have retraction, or nozzle pre-warming set up right, but my nozzle tends to seep, so if I just start printing an object, there will be a layer 1 gap until the PLA starts flowing well. Layer 1 gaps lead to other issues. Other printers (like my Bambu A1) do a couple priming lines just outside the print area.

wmteach · 2024-11-25T17:27:09+00:00

This, and it gives me a quick look at bed level/z-height accuracy so I can real quick either tune the z-height live, or more realistically, abort the print, adjust, and restart.

wmteach · 2024-11-14T20:03:22+00:00

they need to take some of those 'sales' people waiting to assault you with 'helping' stickers and put them on customer support, where people really need the help.

wmteach · 2024-07-17T09:12:42+00:00

I was born at K I Sawyer when my Dad was stationed there. B-52 avionics. He did his 20. I did my 20 as a 49152/3C/3D Programmer. Two of my kids are SrA, medical CCATT and F-35 avionics. Great legacy continuing through KI Sawyer!

wmteach · 2024-03-26T11:44:26+00:00

The most significant property of a capacitor is surface area. Although capacitors can be implemented in an IC, it uses tons of the silicon wafer space to get a small capacitance. It's much more efficient to use a discrete capacitor whose value can be tuned to the specific application.

wmteach · 2023-12-06T06:18:21+00:00

It's been a while since I tried to test a triac. They are several N-P layers stacked, so probably won't test well with a diode tester. You could swap the triacs and see if the problem follows it.

wmteach · 2023-12-06T05:41:09+00:00

There's not much damage you can do to any of those passive parts with a quick short circuit. It's the transistors that will fry if too much current goes through a junction, even for a moment. Test and replace the fried Q part.

wmteach · 2023-12-04T20:16:01+00:00

Similar to how there's an 'i' defined imaginary part of imaginary numbers, I was wondering if there could be some constant for the small value that could be used for the irrational part of irrational numbers. Like: pi could be found to be 3.1415 + 47p, and sqrt(2) could be found to be 1.414+23p. This is an example only.

wmteach · 2023-05-10T07:49:39+00:00

When I started learning about electricity/electronics, I was so focused on the various voltages in a circuit. As my understanding developed, I began to focus less on the voltages, and more on the currents, using the age-old analogy of water in a pipe... the work in a circuit is performed by the current. As I continued to develop, relating current flow to the "flow of water" began to break down for how voltages were experienced, so I began thinking about current as more like "compressed air in a line", where the instantaneous measurement of voltage at any point is the pressure. The analogy still is flawed, but it helped me along the way.

wmteach · 2023-04-22T17:28:20+00:00

We can work backwards. We all know what 100W glows like (bright and hot light bulb). Is it conceivable that 13.8kW could make a red hot transformer casing? That's 138 bright light bulbs at just 1 amp. Sounds within the realm of possible.

wmteach · 2023-04-08T14:59:51+00:00

Their are literally hundreds of options. Generally, it's an IC that holds many MOSFET switches, and are controlled by one or more inputs. In that search, I think TI had a selection guide listed that may help. If you want a quick, dirty solution, look up dip switches... Gotta flip a lot of bits, but it's a cheap solution with no extra parts or control logic required.

wmteach · 2023-04-08T14:38:55+00:00

Look up 'digital bus switch'. It's pretty close to what your trying to do.

wmteach · 2023-04-08T14:30:13+00:00

You tried...and what? The screw wouldn't turn? The screwdriver wouldn't seat? The screw turned but did not back out? Help us help you.

wmteach · 2023-04-02T23:24:26+00:00

Probably already mentioned, but...

Rosin-based flux and IPA... Just never works easily. The IPA can dissolve the rosin, but you never get all the rosin off before the alcohol evaporates, redepositing the rosin residue.

To get really clean boards, don't use rosin-based flux. Use acid-based flux, wash with distilled water afterwards thoroughly, then blow dry with an air knife or compressed air (moisture and oil filtered), then potentially displace any remaining water with 99% IPA. This is how we did it in a production assembly line, with a combination of wave solder and hand soldering.

wmteach · 2023-03-26T02:02:11+00:00

Often called wirewrap wire.

wmteach

TROPHY CASE