Any idea what this is, it seems to measure 12uF

[tonescout]

Hello everyone,

I am rebuilding/refurbishing an old after market Linn LP12 power supply, and I have a noise that creeps in to the power supply (mechanical hum and ZZZ) when it's warmed up, it's as quiet as a mouse when cold. I am swapping out all the old caps as it's 35 years old, and I have not used it for about 20 years. I am also working on cooling the transformers.

But I have no idea what this is, any opinon?> the image is blown up, it's tiny, the red cap.

Scale shown and the red cap I am trying to identify is in the middle of the two 0.68uF white rectangular caps/

Thanks!

 

[Netlist]

It's hard to read. Is it GEW9 25n..?
Could be a NTC.
The hum might come from the transformer. Applying varnish on the laminations and tighten the screws a bit could help.
Finally, that black capacitor doesn't look very good.

Hugo

 

[Elvee]

It looks like a varistor

 

[tonescout]

I ha

It's hard to read. Is it GEW9 25n..?
Could be a NTC.
The hum might come from the transformer. Applying varnish on the laminations and tighten the screws a bit could help.
Finally, that black capacitor doesn't look very good.

Hugo

Black cap already replaced

 

[tonescout]

Where do you get appropriate varnish for transformers from for DIY Application. One of them get's pretty hot too

 

[Netlist]

I use this
Perhaps not ideally suited but it works:

Hugo

 

[tonescout]

Ok - thanks, I will check it out and it's temp performance

 

[Mooly]

Buzzing transformers can be a real problem and not always easy to quieten. One thing we used to do was remove them, heat them gently in a warm oven and then dangle them in a tin of polyurethane varnish for ten minutes.

The magnetic energy (that is the root cause of the buzz) is so concentrated in the core that its not always possible to silence them though.

Same problem with whistling SMPS and old LOPTX's (line output transformers)

 

[tonescout]

Ideally I would like to not have to remove the transformer if possible, and if it is consistently quiet when cooler I am hoping I can tease it into silence with a mini fan and perhaps a heat sink. BUT a bit of varnish would be good too. I also notice it does not have all of it's laminations clamped so I could also add some bolts. The surprising thing is that when the PS is noisy I can hear it's effect on the turntable motor.

 

[tonescout]

Oh, and Mooly my old audio research SP8 that you have helped me with numerous times is now completely hum and noise free, thanks to your advice. I even have the phono stage working well

 

[egellings]

It looks like a varistor

Agree.

 

[brig001]

Could the transformer buzz be DC on the mains?
http://sound-au.com/articles/xfmr-dc.htm

Brian

 

[tonescout]

Agree.

is there any way to confirm what it is be measurement?

 

[Mooly]

is there any way to confirm what it is be measurement?

Not easily. It should read open circuit and only conducts on transient peak voltages above its marked value. They are sized in terms of how many Joules they can absorb.

Your best bet is just to look what it is connected across. A varistor will be placed over either the raw incoming mains or perhaps the secondary windings as low voltage types are available. I think we see '250' on it though.

You would normally use a 275 rating for UK mains.

Some high voltage ceramic caps can look similar.

 

[Citizen124032]

It looks like a varistor

Agree too (#11). It's in the power supply, that would make sense.
A better pic possible to read the complete coding?

 

[Moondog55]

Bearing in mind that my forte isn't electonics; why not separate the power supply into a stand alone unit and use a shielded transformer>??

 

[tonescout]

The whole unit is a power supply actually it just takes 240V and provides 2 feeds of ~ 100V AC to the motor coils in a synchronous motor.

Shielding the transformer is a possibility, but I am not sure what I am trying to shield though as there is 50Hz AC everywhere in the unit.