Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on January 01, 2012, 02:05:11 pm

Title: Classic 50 Screen Resistors
Post by: plexi50 on January 01, 2012, 02:05:11 pm

I was looking at the classic 50 schematic again today and i noticed that there are only 2 100R screen resistors
To me those (2) resistors are only screening the left (2) El84 tubes while the (2) El84 tubes on the right really have no screen resistors on them. Am i right or is this still 2011? Pic's below is one stock schematic and one i think is the way the screens should be wired in

Title: Re: Classic 50 Screen Resistors
Post by: Tiny_Daddy on January 01, 2012, 03:02:18 pm

Yes you are right. Just repaired one of those. Shorted tube vaporized the PCB trace to the screen grid and fried the 390 ohms power resistor in the power supply.

Title: Re: Classic 50 Screen Resistors
Post by: plexi50 on January 01, 2012, 03:42:20 pm

Quote from: Tiny_Daddy on January 01, 2012, 03:02:18 pm

Yes you are right. Just repaired one of those. Shorted tube vaporized the PCB trace to the screen grid and fried the 390 ohms power resistor in the power supply.

Thats what i experienced when i first got this amp. One El84 went bad on me on the un screened  tube side
This is what i just did. Removed two small traces and put in (4) 470r. All tubes are now 470r screened