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Old 27th November 2021, 01:52 PM   #11
Tubelab_com is offline Tubelab_com  United States
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Grounding the tab on the 5 volt regulator is OK in this case. Grounding the tab on the dual Schottky rectifier is NOT. Fortunately, it only needs a small heat sink.

Your washer was probably biting through the solder mask on the board near the mounting hole.

The mounting hole between the regulator and the 300B socket has a gold ring around it which is isolated. There is a space around that ring, and a large solid copper trace under solder mask nearby. The copper trace is the 5 volt supply feed to the output tube heaters. It runs on both sides of the board, and is huge since it would carry over 5 amps in a 2A3 build.

A mounting bolt, washer and nut must stay in the gold area, be insulated, or made of non conductive material to avoid shorting out the 5 volt supply. If the bolt and nut are small enough, leave the washer out or use a non conductive washer.
Tubelab, I blow stuff up so that you don't have to.
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Old 28th November 2021, 12:58 AM   #12
Pooch is offline Pooch  United States
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Yes, I left all the washers out on that side of the board and all is working. I'll replace with nylon washers on both sides, later. Thanks to all for the help.
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Old 28th November 2021, 01:07 AM   #13
Pooch is offline Pooch  United States
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Something else I'd like to add. After I hooked up the cheap Habor Freight meters, for volts and bias. I couldn't get it to bias on one channel....would only come up to 8MA. So I switched the meter positions and all was well. If you use these cheap meters ( which I think are great for the price) watch out for meter failure or wire failure. It could put you on a goose chase.
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