mechanical hum

Bill*B · 26th May 2007, 01:49 PM

Just picked up a pair of tube monoblock amplifiers - Quicksilver KT88s - one is dead quiet, the other has a rather loud mechanical hum. The output signal - through the speakers - is fine. This is a hum at the amp itself, so I assume it's power transfomer related. I can't feel any vibration - the mounting screws are tight - any ideas? Regards, Bill.

beamnet · 26th May 2007, 02:01 PM

Failing power relais (if it has one) or bad transformer. If the latter there are ways to reimpregnate them using diy stuff

Sometimes bad rectifier tubes can cause noise too..

Jeb-D. · 26th May 2007, 11:02 PM

One of my amps does that. I think because do to the nature of the design I had to half wave rectify it which causes an asymetrical flux swing. This is probably not the case for you though, but I know how annoying it is. I've considered filling the transformer end bells with epoxy to dampen it. Or making a dummy load to load the negative half cycle, but this option is a waste of energy and my inner tree hugger won't let me do it.

Bill*B · 30th May 2007, 04:38 PM

Thanks! Bill.

greenvalve · 30th May 2007, 09:42 PM

My first comment ay DIY audio... I thought maybe I could help you out, since I had a mechanical hum on my PS Xformers as well. What finaly cleaned it up was to install a ' DC blocker circuit ' on the 120V primaries.

Looks like this... (thanks Yeo @ diyparadise.com)

26th May 2007, 01:49 PM	#1
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	mechanical hum Just picked up a pair of tube monoblock amplifiers - Quicksilver KT88s - one is dead quiet, the other has a rather loud mechanical hum. The output signal - through the speakers - is fine. This is a hum at the amp itself, so I assume it's power transfomer related. I can't feel any vibration - the mounting screws are tight - any ideas? Regards, Bill.

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26th May 2007, 02:01 PM	#2
beamnet diyAudio Member Join Date: Jun 2004 Location: enschede	Failing power relais (if it has one) or bad transformer. If the latter there are ways to reimpregnate them using diy stuff Sometimes bad rectifier tubes can cause noise too..

26th May 2007, 11:02 PM	#3
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	One of my amps does that. I think because do to the nature of the design I had to half wave rectify it which causes an asymetrical flux swing. This is probably not the case for you though, but I know how annoying it is. I've considered filling the transformer end bells with epoxy to dampen it. Or making a dummy load to load the negative half cycle, but this option is a waste of energy and my inner tree hugger won't let me do it.

30th May 2007, 04:38 PM	#4
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	Thanks! Bill.

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