Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: amado@usa.com on February 12, 2021, 07:20:06 pm
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Amado Navas
I am here looking for advice, just bought my 1st Tube Amp, after owning one in in the '80s, and getting a little hiss noise while is just sitting idle. The unit is a Fender Twin Reverb 65 Reissue, made on 2017. Bought it used as a scratch - dent at Guitar Center. The Amp plays OK, even looks new, but the hiss remains while it is idle, volume knobs at zero. Are these Amps supposed to be dead quiet? Should I replace the Tubes it came with? (Standard GT Chinese I think) Or try to Adjust the BIAS? Or move the Tube around? Any help is appreciated.
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A certain amount of (white or pink noise) hiss is normal. This is usually quiet (but still faintly audible) hiss when both vol controls are cut completely
'Hiss' is also normal/likely if the reverb level is turned up a bit (even if both volume controls are cut). The reverb recovery stage has a higher S:N ratio that the input stages and so is quite a bit more sensitive to any 'noise floor' noise - including hiss. Turn the reverb level down to see if any of 'the hiss' goes away.
Hum would not be that normal (unless the output tubes were unbalanced). But that's different from hiss.
Intermittent crackling/static discharge noise with all volume and reverb level controls completely cut is not normal, and is more likely to be either a bad tube, loose pin clamp(s) on one (or more) of the tube socket(s), or a cold solder joint or cracked jumper lead, or failing component (e.g. resistor or capacitor) somewhere inside the amp. But that is also different from normal hiss.