• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Troubleshooting hum in 12b4 preamp.. finally almost done!!

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DF96, thank you for the explanation. The transformer I am using for the heaters does not have a center-tap.

I think I am seeing the error of my ways here. My circuit goes like this; Transformer with no center tap through resistor (to lower voltage) to tube on the left, and tube on the right (connected in paralell as you suggested).

I grounded the heater center tap on both tubes to the same location. Sounds like what I did is redundant and can cause hum.

Thanks so much.
 
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