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76.174.175.12
Luckily I had some resistors to drain the voltage.
I turned the amp on again and I CAREFULLY measured 517v.
That's the rating of the power supply caps.
What could I have possible done wrong?
I'm working on a variation of the morrison micro amplifier, but using 300b tubes and a 12at7.
2A3 operating points in a direct couple situation.
Follow Ups:
A metal bracket to attach a metal cap can leave your top plate energized. Be careful when you ground the amp to the AC line ground and flo=ip the switch that the short does not blow up the capacitor and injure you. Measure resistance to ac ground for all exposed metal and parts to find your short. Aways check your parts for ground paths.
I agree, all exposed metal needs a path to safety ground. The top plate, the body of transformers, a metal capacitor body, etc. all need to be grounded for safety. "YOU" may actually do nothing wrong, but a part could fail, a wire can get pinched, a wire could bird cage under a solder joint etc. You don't want a single part failure (and the cascade of parts that will also break from that failure) to hurt someone. Don't plan on those other parts failing open either. Those three things I just mentioned I have seen happen and I have seen people shocked (me included) when test racks etc. where not properly grounded.
I used to strongly object to tying signal ground to chassis through back to back (paralleled) diodes. But I've loosened up on that and believe if the diode's I^2*t rating at operating temperature is more that twice that of the line fuse, I can sleep at night. And yes, you can put more than 1 back to back pair of diodes in series to allow more chassis noise voltage. You may need two in series because a diode can be considered to be conducting a silly low voltages in some cases (0.23V). An all in one diode bridge (see below) with "+" tied to "-" and one "~" to chassis and the other "~" to signal ground is a candidate. Just buy a standard recovery diode with an I^2T many times that of the fuse rating.
Don't use a diode between chassis and safety ground. You'll want a connection there that can pop your 20A mains breaker for that connection.
See the link below for first "hit" from google that had a decent explanation of the I^2T issue.
After you ground chassis to safety ground. I would start by visually looking at the terminal strips used to hold parts and connection in the power supply path. The terminals that also support the strip to chassis are easy to accidentally connect to something.
Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.
. . .Oh!. . .Remember: Modifying things voids their warranty.
Every chassis should be firmly connected to the AC earth ground wire. Then, if something shorts, the fuse will pop instead of your heart.
Thanks!
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