Excessive hiss from tube amp - need to replace tubes? - Live Sound https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/ Guitar Noise Discussion Board en-US Fri, 05 Jun 2026 02:04:50 +0000 wpForo 60 Re: Excessive hiss from tube amp - need to replace tubes? https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-293960 Tue, 27 May 2008 01:02:45 +0000
Hiss is often due to bad tubes, usually from the first preamp tube, especially in high gain amps, such as the 5150. Begin by replacing that one with a good tube and see if goes away. Hiss can also come from bad or failing resistors or capacitors, especially those used for cathode bypass.

Hum is 60/120 Hz noise often caused by failing electrolytics in the power supply. They typically have a 10-15 year lifetime.

How old is your amp?]]> Live Sound PRNDL https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-293960 Re: Excessive hiss from tube amp - need to replace tubes? https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-293922 Mon, 26 May 2008 19:05:50 +0000 Live Sound defenestration https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-293922 Re: Excessive hiss from tube amp - need to replace tubes? https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-293918 Mon, 26 May 2008 18:08:29 +0000 http://geofex.com/ Click on "Tube Amp Debugging Pages." Read. :D]]> Live Sound Ricochet https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-293918 Excessive hiss from tube amp - need to replace tubes? https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-31875 Mon, 26 May 2008 17:18:55 +0000
# Five 12AX7 preamp tubes
# Two 6L6GC power tubes

Hiss is emitted with no guitar plugged in. Hiss volume increases as pre and/or post volumes are increased. My father who studied EE 25 years ago (heh) visually inspected the pre tubes and saw no damage. How would I determine the source of the hiss and eliminate it? It's really, really annoying!]]> Live Sound defenestration https://guitarnoise.forum/live-sound/excessive-hiss-from-tube-amp-need-to-replace-tubes/#post-31875