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Old 7th February 2018, 04:42 AM   #11
wrenchone is online now wrenchone  United States
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Dremel will save the day on R21A on the boards I have - layout is fixed with new rev. Thanks for spotting.
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Old 7th February 2018, 01:59 PM   #12
12E1 is offline 12E1  United Kingdom
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Quote:
Originally Posted by wrenchone View Post
Dremel will save the day on R21A on the boards I have - layout is fixed with new rev. Thanks for spotting.
Dremel is one approach, but I prefer to score across the track with a craft knife or similar with two cuts to create a narrow strip. Then the application of heat from a soldering iron to the isolated strip allows the copper to come away from the substrate very cleanly to create a neat break in the track.
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Old 7th February 2018, 05:21 PM   #13
wrenchone is online now wrenchone  United States
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Too much drama and trauma, especially since the board is already stuffed - Dremel will work better and faster. I'll just isolate the offending patch with two cuts, and bridge around with a jumper.
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Old 8th February 2018, 09:23 PM   #14
wrenchone is online now wrenchone  United States
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My Mouser order should come in today, so I can finish stuffing the board and get it on the bench. I'll probably end up using some Fisher 500B or 500C output transformers I have lying around. I also have some Sherwood iron that might work. First off, though, I'll be powering up the board with some bench supplies.
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Old 12th February 2018, 05:55 PM   #15
wrenchone is online now wrenchone  United States
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Semiconductors, balancing pots, and filament leads are installed. Once I make up some input and feedback cables, the amp will be ready for bench testing.
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Old 19th February 2018, 03:10 AM   #16
wrenchone is online now wrenchone  United States
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Cables & connectors & such are in place, and the output XFMRs have been fitted with connectors. Output transformers for the shakedown cruise will be a certain rusty pair (not so rusty, really) that George/Tubelab bequeathed to me a few years ago for the price of transport. I've never been one to say no to output iron... Tuesday, this beast will get slung onto the bench at work for a first power-up.
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Old 19th February 2018, 03:25 AM   #17
Tubelab_com is offline Tubelab_com  United States
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I just turned one of their brothers into a magnet. An arc from plate to ground, or the PC board plating that was formerly ground, now nonexistent, where the B+ was a 650 volt 1.7 amp power supply that has 1000 uF across it's output will do that.

Those transformers are 6600 to 0-4-8-16 ohms. They actually work better at 3300 to 0-2-4-8 ohms. I was pushing the meter north of 160 watts per channel through a pair when the insulation on a plate to plate feedback resistor broke down.

After cutting out the resistor and drilling out the charred PC board that channel was weak, distorted and drew too much current when driven hard. That's when I noticed that a screwdriver sticks to the OPT. I may try to degauss it when I find my variac.
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Old 19th February 2018, 04:07 AM   #18
wrenchone is online now wrenchone  United States
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I don't intend to be that awful to my rusty pair. When bias levels are settled and output is verified, the rusty pair will be replaced by some Fisher output iron.
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