Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: idontknowyou on June 29, 2021, 02:33:33 pm

Title: signal being fed to cathode?
Post by: idontknowyou on June 29, 2021, 02:33:33 pm

Just a schematic question here. I have a Dukane tube PA amp and I was really surprised when looking at the 2nd gain stage in the schematic. The first half of a 12ax7 operates as I would expect, signal to the grid and coming off the plate, but then the plate is tied directly to the cathode of the 2nd half of the tube, and the 2nd grid is tied to ground, and even bypassed with a cap and resistor, as if it were acting as a cathode?! Just very very curious as to how exactly this functions. Would love a little explanation if anyone is interested in taking the time. Thanks!

Title: Re: signal being fed to cathode?
Post by: sluckey on June 29, 2021, 02:46:37 pm

Read about it here...

     http://www.valvewizard.co.uk/cascode.html

Title: Re: signal being fed to cathode?
Post by: idontknowyou on June 29, 2021, 02:55:36 pm

Very cool! Thank you!

Title: Re: signal being fed to cathode?
Post by: Willabe on June 29, 2021, 04:53:53 pm

Which Dukane amp model is it?

Can you post the full schematic?

Title: Re: signal being fed to cathode?
Post by: sluckey on June 29, 2021, 04:59:25 pm

https://el34world.com/charts/Schematics/files/Dukane/Dukane_1a385.pdf

Title: Re: signal being fed to cathode?
Post by: Willabe on June 30, 2021, 10:16:23 am

Thought he might have had a schematic Doug didn't have.