WOPL 700B A/C hum ?

[mattoe]

I have had a preamp causing a hum.

The first thing I did was to remove the inputs completely....

 

[jbeckva]

Can we see some pics? Star ground.. inputs..

 

[Gepetto]

Yes Sir,

the RCA's ground via a copper strip between and common to both ... Not directly to the chassis....
The drinking straw trick ??? That's new .... I can only assume insulating the bolts as they run the length of the
laminated stack ?

Matt

Yes and fiber washers under the head and nuts of the retaining bolt. The bolt has to be completely insulated from the transformer stack. It minimizes eddy current losses in the transformer stack and reduces the transformer idle current.

 

[mattoe]

Yes and fiber washers under the head and nuts of the retaining bolt. The bolt has to be completely insulated from the transformer stack. It minimizes eddy current losses in the transformer stack and reduces the transformer idle current.

Ok I can see that as plausible.... I will source out some hd fiber washers and will use some heavy wall shrink tubing on the bolts ....

Great thought Thank you !


When I get it back apart ..(again) I will post pics of the rca's and the connections to the "star " grond....

 

[NavLinear]

What manual do you have Dennis, mine doesn't even mention hum>??

Hey Lee - here's the Service Manual for the 700/700B with the hum section.

 

[laatsch55]

Thanks Dennis!!

 

[mattoe]

Hey Guys,

I finally made it back to the 700 hum.... I removed the transformer bolts and put fiber washers at both ends , effectively isolating the bolts from the core... Poked around and put things back together..... No more hum.... Hard to say if the bolt washers did the trick or simply the act of disassembly and reassembly..... Cheers Thanks for the suggestions!

Matt

 

[Gepetto]

Glad to help Matt. I do that on mine...learned that fact a long time ago (mid-late seventies) when I was specifying transformers in a small engineering company.

 

[WOPL Sniffer]

Glad you got it fingered out...