Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mr.Death on October 14, 2022, 02:27:24 pm

Title: Burnt screen grid resistor, my mistake.
Post by: Mr.Death on October 14, 2022, 02:27:24 pm

I was checking bias today with my new probe and when I reinstalled the tube I installed the tube incorrectly, the key was off by one pin. My mistake and I'm ashamed of it  :sad2:.....  :BangHead: I ended up burning one screen grid resistor in the process. When I inspected the amp I noticed R30 (1K 20watt sand resistor) was hot to the touch and a little discolored. It measured fine with the multimeter. I ordered the 2 47R resistors for the screen resistors. Should I also replace the 1K20watt? Like I said it still measures within spec. Leave it? Thanks. Schematic for reference. Resistors circled.

Title: Re: Burnt screen grid resistor, my mistake.
Post by: mresistor on October 14, 2022, 06:02:10 pm

I never like to leave burned or overheated components in an amp.  What happens when it is under load again?    Just replace it as they are cheap.

Title: Re: Burnt screen grid resistor, my mistake.
Post by: Mr.Death on October 14, 2022, 07:25:46 pm

Just happened this morning and Ive yet to replace the components. Having a hard time locally finding a sand cement resistor for the 1K 20 watt.

Title: Re: Burnt screen grid resistor, my mistake.
Post by: Mr.Death on October 15, 2022, 01:29:41 pm

I replaced the burnt 47r resistor and everything works as it should, lesson learned.

Title: Re: Burnt screen grid resistor, my mistake.
Post by: sluckey on October 15, 2022, 02:29:59 pm

Quote from: Mr.Death on October 14, 2022, 02:27:24 pm

I installed the tube incorrectly, the key was off by one pin.

How did you do that unless the key on the tube was missing?

Glad the damage was minor.