Resistors Making An Amp Quiet...

[sbeckett]

Why do these 100 Ohm Resistors eliminate single coil guitar up against a fluorescent light noise from my amp? Idle noise is practically non existent with the amp and guitar volume turned all the way up. The amp appears to operate normally otherwise. When I remove the resistors the amp has about the same amount of idle noise as a Blues Junior.

[PRR]

If there is NO connection heater-circuit to amplifier common, lots of line hash is radiated from heater wires to amplifier nodes.

Grounding one side of the heater is a big improvement. And saves a buck if you use the chassis for heater return. That's how radios were wired.

"Balancing" both heater lines is even better, and worth the extra pennies in high-gain amplifiers.

There's no normal case where you DON'T want a ground reference on heater circuit. It may be elevated, but totally floating invites worse trouble than just hum.

[sbeckett]

Thank you!

[pdf64]

Also DC elevation of the heater circuit as shown can help to prevent heater current sneaking through the heater to cathode insulation of the valves.

[scstill]

http://www.valvewizard.co.uk/heater.html