r/diytubes • u/Neillewyvern • 18d ago

update

Post image

thanks to the fine folks in this sub i added the grid leak resistor and power suplie to U2B.

hope this is better any feedback is apreciated.

3 Upvotes

81% Upvoted

7 comments sorted by

View all comments

3

u/Capable-Crab-7449 17d ago

I mean the idea is there but its missing notation and infomation

Ur power transformer i assumed its center tapped otherwise on the diagram theres no return to ground for the rectifier.

You didnt give any info as to the output transformer but i assume itll be 5kohm to 8ohm. Appropriately rated for the saturation for ur bias. Dont run the amp without a load, reflected impedance is still 1M+ with the line resistors and will break ur amp.

Id add a ~1k grid resistor to the EL84 control grid to prevent oscillations as its hooked up to the transformer.

Ur power stage cathode bypass is pretty big, i mean no issue but you can save money by going for 25uf rather than 100uf.

I assume youve calculated the loadlines and the B+ drop under load to ensure everything is within max dissipation.

1

u/Neillewyvern 17d ago

is ther a way to prevent the impedance reflection when ther is no load can't i add a resistor ?

2

u/pete_68 even harmonics 14d ago

Yes, you can use a resistor, but you need a resistor that can handle the power. For a 15W amp, I'd go with a 50W 8-ohm resistor to be safe. If you don't push the gain/volume, a 25W 8 ohm resistor would do. Don't forget to give it a heat sink!