Subject: heater hum,.. a proposed article
    Thank you for your many fine articles and efforts. Acting on your invitation I am proposing a discussion of heater circuit analysis with a specific focus on the issue of grounding, or not, or floating the heaters a certain voltage above ground, sometimes at different levels between valves used in the same circuit. Where and when and why and what to ground I do not understand in the least. I have built the simplest 3 valve "Champ" circuit possible and still have unusable noise problems which some people have suggested may be due to my heater arrangement. I have tried ac both grounded and not, floated with a .1µF cap to ground and not, with and without 100 ohm resistors providing a pseudo-center tap, an actual center tap, heavily filtered DC, also floated and not, as well as dedicated heater transformers in a variety of configurations. When a man is plagued with hum, the rest of his life is meaningless. Any recommendations or general discussion you might offer would be appreciated. Thank you,

-s.

   I hate noise. I routinely turnoff the refrigerator when I play music. And I long for quieter power supply fan on my computer.  In other words, I feel your pain. So here is the first rules for hum reduction. Know what frequency you are dealing with. If the hum is 120 Hz and the heaters are AC fed, then the problem lies with the power supply not the heaters. Next, never let the AC ground carry any heater current, whether the heaters are run on DC or AC. Furthermore, do not use the chassis as a current carrying component. Instead, tightly twist the heater wires and arrange the wires away from the signal carrying components. Next, try different tubes. For example, some 12AX7s have a heater element that is folded back and forth within the cathode sleeve, while others have a helically wound element. The helical element wins, as it eliminates much of the potential hum.

   One possible problem I should mention is that   maybe the power transformer is mis-tapped at the B+ winding. For example, a 600 VAC CT transformer that actually measures 294-0-304 volts. This transformer will create a strong 60 Hz noise component that can be eliminated by adding small 10 VAC transformer in series with the weak half of the primary.
   (One trick definitely worth trying is to use a car battery for the all the heaters in a system. A friend uses a Sears Die Hard for this purpose and it works truly well.)

Subject: Help
    Hi, I have some questions and I was wondering if you could help me out. In order to graduate from high school, I have to do a senior research project.
    For my subject I want to try to compare the signal outputs of tube and solid state or transistor amplifiers. I also have to create a product and wanted to build an all tube 50-watt guitar amplifier. I would appreciate any information that you could give me or help on building my project. Thanks so much!
Sincerely,
-Nick

    Nick, just I do not have the time to spare, unfortunately, as I have some ideas for what to test for. But if anyone is willing to help out, we will relay their e-mail to you. One article you must read is in the August 1998 of the IEEE Spectrum by Eric Barbour titled, "The cool sound of tubes."

Subject: article request
    Howdy, I love your webzine. Something I have always wanted to see is an article on power supply design with lots of practical advice such as how to make them safe (capacitors between wall supplies and their values) how large to use filter caps (what is practical and what is not), how large to make bypass resistors. Apparently you shouldn't make the first filter cap too large,