[NoDisco]

So...I've gone back to tube monos/pre versus a tube integrated. It's the fall after all!

I get a little hum. Pre is plugged into wall through a grounded cord. Monos are plugged into a ps audio quartet using grounded cords. The quartet is plugged into the wall using a grounded cord.

My first instinct would be to remove the grounded  cord from the quartet and run an ungrounded plug to remove the hum.

Will this help? Do I need to unground the amps plugged into the quartet as well?

Thanks.

[Speedskater]

I would plug everything directly into the same outlet strip.
If you are using RCA interconnects, make sure that the interconnects are coax with a heavy braided shield.
Anything else attached to the system?

[NoDisco]

I'm running all balanced. The entire system (computer dac amps) goes thru the quartet. The Pre for sure likes the wall for some reason. This much I know. I'm using a Woo WA22. It's very finicky about its grounds I've noticed.

[ketcham]

Try removing the PS power strip and see if the issue goes away.

Allnic (tube) electronics also exhibit this issue with PS Audio.

[Folsom]

If it's a laptop source try unplugging it from charger and see if it's still there.

[Speedskater]

With XLR balanced interconnects, the system shouldn't hum. But anyway get a cheap pair of XLR interconnects, open the shells at  the receive end and cut the shield wires.

[NoDisco]

The power transformers on the power amps have a noticeable hum when the pre is in the chain. This is independent of 2 prong or three prong power cords that I'm using. It's definitely the pre not getting along with the power amps. Unfortunately, the manleys I have hate the wall power I have with a passion.

[Speedskater]

How old are the Manleys? What type of power supplies do they have?

[NoDisco]

Well over 10 years old. The input transformers are non-toroidal.

[Speedskater]

Are the Manleys' power transformers separated from all the other audio units?

[NoDisco]

By a foot or more.

[Folsom]

Are the tubes good?

[NoDisco]

new. I really think its a ground loop between the pre and the amps. When I used the pre in front of an integrated, I had the same problem. That was mitigated by plugin both into the wall sockets. I cant plug the manleys into the wall sockets since they'll really really hum, and that's w/o the pre. One of the amps went back to the factory and got a clean bill of health and both play beautifully.

[RPM123]

You could try a pair of these power cords with ground lift switches and polarity reversal.

https://www.tlp-audio.com/powerCords.php

BC63 and BC64

"The BC63 and BC64 are identical to the 61 and 62, but with some added features. Both these power cords have a control box integrated into the power cord. Each control box has two switches. The first switch is a two-position switch that allows the user to lift the ground connection. This is very useful in hunting down ground loop problems. The second switch is a three-position switch that allows the user to reverse the line polarity. Position one is normal (live-to-live, neutral-to-neutral). The center position is open, to prevent arcing during transition. The third position is reverse polarity (live-to-neutral, neutral-to-live). Not all homes are wired correctly, and some components are very sensitive to line polarity. We have had very positive feedback from professional installers about the usefulness of these features."