Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on August 20, 2022, 03:04:52 am

Title: Gibson GA50 question
Post by: Leevi on August 20, 2022, 03:04:52 am

What is the idea/benefit of the 250p-330K coupling from the PI plate to the power tube plate?That is missing from the GA50T.
https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga_50.pdf
https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga50t.pdf
/Leevi

Title: Re: Gibson GA50 question
Post by: sluckey on August 20, 2022, 05:13:35 am

Quote from: Leevi on August 20, 2022, 03:04:52 am

What is the idea/benefit of the 250p-330K coupling from the PI plate to the power tube plate?

That is a local negative feedback loop.

Title: Re: Gibson GA50 question
Post by: Leevi on August 20, 2022, 05:21:21 am

I have built this amp several years ago and I left the loop away.Maybe the reason was that I didn't notice any difference if it was connected or not.Anyway hard to remember./Leevi

Title: Re: Gibson GA50 question
Post by: pdf64 on August 20, 2022, 07:41:37 am

Fender did something similar, but full bandwidth, with the ab165 bassman https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_ab165_schematic.pdf