Info on this amp???

[Bernardduur]

Hey all!

As to start, I must say I am quite new here; I've been building preamps a long time but never got up to build real amps.

Since a friend build me an amp I am quite eager to venture into this world


Now on the topic
I recently got this amp from a friend who wanted it checked. The problem: the amp starts to hum when the amp is on too long. I never saw something like this amp and wanted to ask:

- Can I improve this amp??
- What is the origin of the amp

http://www.student.ru.nl/r.kerkhof/Amp_1.jpg
http://www.student.ru.nl/r.kerkhof/Amp_2.jpg
http://www.student.ru.nl/r.kerkhof/Amp_3.jpg
http://www.student.ru.nl/r.kerkhof/Amp_4.jpg

[Bernardduur]

Small question;

I want to replace the ELCO's in this unit; have a hard time finding 80 uF versions, so could I use some 100 uF's or is the 80 uF that important?

[Enzo]

The values are not critical.

If you are doing that for the hum, consider a new power tube. Does the hum go away when you turn the volume control down? Does the hum go away if you pull the preamp tubes?

The schematic looks wrong to me. The 283V is wired to the screen of the power tube, while the plaet supply is drawn as the 229v. I think the output transformer should be drawn connected to the plate, and the screen then connected to the 229v B+ node.

[Bernardduur]

Thanks man!

The schematic was wrong; now it should be like the original

The hum went away when I replaced the ELCO's

Thanks!