Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JustMike on December 02, 2020, 09:26:35 am

Title: 93 Fender Super Humms
Post by: JustMike on December 02, 2020, 09:26:35 am

 This amp was in a Beach bar for years. I cleaned it up, recapped it, replaced the 6l6's and one bad 12ax7. It works, but there is a 120hz(?) hum present all the time and it's not affected by any volume control. It doesn't change when I insert a cable to the front input jacks or the send & return jacks. The caps I replaced were the 7- B+ caps. I suspect there may be a corroded or rusted ground connection? Anything else I should be looking for? preamp tubes perhaps?

Title: Re: 93 Fender Super Humms
Post by: Latole on December 02, 2020, 09:47:08 am

Is the hum was there before you work in ?

And what about bias caps ?
You can check ripple to see if they are bad or not

Clean all tubes's sockets.
Any mod on the amp ?

Title: Re: 93 Fender Super Humms
Post by: Latole on December 02, 2020, 10:07:02 am

Did you put filter caps with polarity ?

Check ripple ; no more than fews AC volts

Title: Re: 93 Fender Super Humms
Post by: JustMike on December 02, 2020, 10:14:15 am

Thanks Latole, but I don't have a scope.

Title: Re: 93 Fender Super Humms
Post by: Latole on December 02, 2020, 10:15:41 am

You don't need a scope , use voltmeter in AC scale.

Is the hum was there before you work on amp ?

Title: Re: 93 Fender Super Humms
Post by: Latole on December 02, 2020, 10:28:10 am

Check if heater ground through 47 ohms resistor is good