Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silat on February 28, 2017, 10:18:15 pm

Title: Ab763 Hum issue Amp played great up until now.
Post by: silat on February 28, 2017, 10:18:15 pm

My blackface clone has a hum that stays the same level even if you turn the volume all the way down. Has anyone ever had this happen I have let the amp sit and have not played it for awhile and it developed this loud annoying hum at  loud level. In one channel you can play the guitar through and hear it but nothing through the other channel but that hum.

Thanks in advance for any input.

Silat

Title: Re: Ab763 Hum issue Amp played great up until now.
Post by: Raybob on March 01, 2017, 01:24:51 am

What is "a while"?  How old are the filter caps?

Title: Re: Ab763 Hum issue Amp played great up until now.
Post by: silat on March 01, 2017, 06:25:56 am

Filter caps are new. It is a new clone at least a year old. I have let it sit and worked on building other amps.

Title: Re: Ab763 Hum issue Amp played great up until now.
Post by: silat on March 02, 2017, 08:56:27 am

! No longer available (http://www.youtube.com/watch?v=GrVtX0QGNls#)

This 60 cycle hum that does not change when you turn the volume up or down is just what my amp is doing.

Title: Re: Ab763 Hum issue Amp played great up until now.
Post by: silat on March 02, 2017, 09:06:22 am

https://www.youtube.com/watch?v=GrVtX0QGNls (https://www.youtube.com/watch?v=GrVtX0QGNls)

The video above says a 60 cycle hum is a tube. A 120 cycle hum which sounds different is a filter capacitor.

Title: Re: Ab763 Hum issue Amp played great up until now.
Post by: silat on March 02, 2017, 10:10:51 am

It was nothing but a bad tube at V6 12At7.... Changed it and it now plays great.