Vacuum Tube OTL power amp!!

[dady]

LOOKS IMPRESSIVE

[kevinkr]

Cool! Any idea why the toroids are buzzing? Are you for example saturating the core every half cycle - if so some very small power resistors in series with windings might get you out of the woods by limiting the peak current to something more reasonable..

Mechanical buzzing - can you isolate the toroids on sorbothane mats or similar?

[flatheadmurre]

First i suspected DC from the mains since it sometimes is dead silent and some other times buzz loudly.

A DC-trap didn´t change the behavior.

So either a badly fabricated toroid or something i missed ??

[atmasphere]

Originally Posted by flatheadmurre

First i suspected DC from the mains since it sometimes is dead silent and some other times buzz loudly.

A DC-trap didn´t change the behavior.

So either a badly fabricated toroid or something i missed ??

When you say 'DC trap' this was something on the mains side of the transformer? A set of diodes bypassed by electrolytics? If no, then you need to add this, if yes, noisy transformer.

[flatheadmurre]

Yes, tried from 2-7v diode drop on the mains side same result so must be the toroid itself.

OR..???

Strange that it comes and goes.

A noisy toroid could change during heatup, but this comes and goes.

[atmasphere]

Were the diodes bypassed by electrolytic capacitors?

[flatheadmurre]

Yes.

2pcs 10mF back to back.

[atmasphere]

Hm. I would try something more like 1000uf...

[flatheadmurre]

Originally Posted by atmasphere

Hm. I would try something more like 1000uf...

Why 1000uF ?

My experience is that nothing below 4700uF works good.

10mF is double that.

[atmasphere]

Originally Posted by flatheadmurre

Why 1000uF ?

My experience is that nothing below 4700uF works good.

10mF is double that.

In the US, the u means 'micro' and quite often 'm' means micro too.

You must mean 'mill' as in milli-farad'?

If that is true then you will simply have to replace the toroid(s) or find some way to isometrically isolate them from the chassis.