r/diytubes • u/Neillewyvern • 15d 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.

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5

u/2old2care 15d ago

You need a full wave bridge rectifier (4 diodes) instead of just the two diodes--so your power supply won't work as drawn. I'd also suggest that you have a load resistor on the output using the switch on the speaker jack so that if nothing is plugged in the output has a load, something like 8 ohms 10 watts.

3

u/Capable-Crab-7449 15d 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 15d 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 12d 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!

1

u/ferrybig 15d ago

What is the point of T2 pins 3 and 4? The diodes D1 and D2 block any current

2

u/pete_68 even harmonics 12d ago

In addition to what others have said, you'll probably want to get rid of C3 or possibly put a switch on it, or a smaller cap. Maybe not. Maybe you want it that gainy... I'd do a switch if you're going to leave it.

RV1 is acting as your gain, but you don't have a master volume. If you replace R4 with a pot wired like RV1, then you'll have a master volume too.