Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on December 07, 2018, 06:59:22 pm

Title: Power Transformer physical buzz
Post by: mresistor on December 07, 2018, 06:59:22 pm

I've got a Fender Bandmaster that has a PT the physically vibrates, it is something you can feel but it isn't detectable in the sound of the amp. I've read this can happen if the PT has a manufacturing defect or the steel laminations are separating..  Upon physical inspection the PT looks normal and doesn't exhibit signs of the laminations separating.  So I guess there is an internal problem that is not detectable with the eye. What do you guys think of this?  Would you replace the PT or continue to use it.  It feels like a vibrator.

Title: Re: Power Transformer physical buzz
Post by: shooter on December 07, 2018, 07:10:21 pm

did you check the bushings that are on the screws, if they get crispy, might be a problem.

just thinking out loud, maybe with endbells off, you can see the bobbin moving?

are the volts correct or has it lost some?

that's all I got

Title: Re: Power Transformer physical buzz
Post by: mresistor on December 07, 2018, 07:34:43 pm

Good Points Shooter..  I'll get it out of the cab tomorrow morning..  and let you know

Title: Re: Power Transformer physical buzz
Post by: Willabe on December 07, 2018, 09:09:37 pm

You might need to snug the PT bolts up some.

And/or like shooter said the bobbin might be loose and need to be shimmed to snug it in place.   

Title: Re: Power Transformer physical buzz
Post by: mresistor on December 19, 2018, 12:42:16 pm

Tightened up the transformer bolts and it solved the problem.  Strange though it looks like someone replaced them, or, they aren't the same as I am accustomed to. It was made by Better Coil & Transformer EIA code 831  in '68. The bolts take a 1/4" nut driver.