I built a tube preamp in one of those Radio Shack plastic boxes and not sure about a couple of grounding issues. It sounds pretty darn good but does have a slight hum. So questions,
1. I used a chassis mount IEC so not sure where to put the safety ground blade
2. I used back to back power transformers, I'm using 6922 tubes and running them in series at ~12vdc. Not sure what to do with that center tap. (Attached)
3. I didn't use the shield pin (9) of the 6922 tubes. Should I and where would that go?
Thanks
1. I used a chassis mount IEC so not sure where to put the safety ground blade
2. I used back to back power transformers, I'm using 6922 tubes and running them in series at ~12vdc. Not sure what to do with that center tap. (Attached)
3. I didn't use the shield pin (9) of the 6922 tubes. Should I and where would that go?
Thanks
Attachments
Moved as requested. 
If the entire box is plastic, then you could connect the IEC safety ground to the audio common,
either directly or through an impedance or a diode block. If the front panel is metal, connect it there.
I would not connect the center taps together, just tape each one off separately.
Shield pin goes to the audio common (0V).
either directly or through an impedance or a diode block. If the front panel is metal, connect it there.
I would not connect the center taps together, just tape each one off separately.
Shield pin goes to the audio common (0V).
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Thanks Rayma. I did try your suggestions but the hum is still there, although slightly different. I think it might just be the fact that I crammed a lot of stuff in a pretty small box. I may re-build it in a larger metal case and add a phono stage.
Sounds like a good idea. Always use a box that is too big, rather than too small.
Keep the input stage close to the input RCA socket.
The transformers, if close to the circuit, may be inducing 60Hz hum as well.
Keep the input stage close to the input RCA socket.
The transformers, if close to the circuit, may be inducing 60Hz hum as well.
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