Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Electron Tornado on October 12, 2019, 03:38:48 pm

Title: Epiphone Valve Jr questions
Post by: Electron Tornado on October 12, 2019, 03:38:48 pm

I am working on a Valve Jr project, and have a few questions. I will reference the schematic here: http://www.muzique.com/news/images/Epi1.gif (http://www.muzique.com/news/images/Epi1.gif)

1. If I remove R7, and reduce R6 (maybe even add a switch to bypass it), should I add a grid stopper to V1B?

2. I have heard of people adding a negative feedback loop to this a-la the Fender Champ. If anyone has done that mod, how much of a difference did it make?

3. What are the pros and cons of adding a resistor to the screen grid of the EL84?

Title: Re: Epiphone Valve Jr questions
Post by: vampwizzard on October 15, 2019, 07:51:50 am

theres a ton of info out about this particular amp..

general info, last link is a project where they added grid stoppers:
https://el34world.com/Forum/index.php?topic=514.0 (https://el34world.com/Forum/index.php?topic=514.0)
https://el34world.com/Forum/index.php?topic=21489.0 (https://el34world.com/Forum/index.php?topic=21489.0)
https://courses.physics.illinois.edu/phys406/sp2017/Student_Projects/Spring10/Robert_Marshall/R_Marshall_P498POM_Final_Report_Sp10.pdf (https://courses.physics.illinois.edu/phys406/sp2017/Student_Projects/Spring10/Robert_Marshall/R_Marshall_P498POM_Final_Report_Sp10.pdf)

I think the amp is useable as is without a NFB circuit but a good sound example can be found on YT with Kley De Jong's Valve Jr rebuild Pt 7.