Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Nathan on November 21, 2023, 09:13:13 am

Title: PT diagram
Post by: Nathan on November 21, 2023, 09:13:13 am

Guys, I am having a brain fart and can't seem to find the info by searching...


In the diagram below, the PT should be read as 275-0-275 correct? Thus 550V secondary w. center tap?   

(http://guiguijones.free.fr/Electronique%20&%20Bouine/electronique/Schema%20Amplis%20Effets%20etc/Amplis/Mesa%20Boogie/bluangps.gif)

Then why are we getting 180V at point E? Is it because there is only half wave rectification with diodes?


FYI this is the Mesa Blue Angel power supply with solid state rectifying the preamp and tube for the power tubes... 


Thanks for your help!

Title: Re: PT diagram
Post by: pdf64 on November 21, 2023, 09:25:17 am

Here’s the schematic for the blue angel https://el34world.com/charts/Schematics/files/Mesa_boogie/Boogie_blueangel.pdf
Point E of the 2 schematics is totally different.
It’s 180V due to preamp current being drawn via 49k of HT dropping resistance.
At the reservoir cap it’ll be much higher.

Title: Re: PT diagram
Post by: Nathan on November 21, 2023, 09:48:44 am

Thank you kind sir, don't know why my link to the image isn't working but you have the right one...


But my assessment is correct that it is a 550V PT?

Title: Re: PT diagram
Post by: pdf64 on November 21, 2023, 11:17:42 am

Yes, 550V CT = 275-0-275V.
There should be around 380V at the reservoir cap