KEL84 hum when source plugged in?

[John Caswell]

So how is your input signal screen going to get grounded? Initially ground it at both ends, you can always cut it out after.

John

[Richard]

Hi Phill,

Greg should be able to help but if not PM me your email address and I can send the build sheets and diagrams but they won't explain the earth routing.

For your construction you'd identify the earthiest point (PSU cap negs) and connect that to a nearby tag to make a star ground point. Hopefully your builder has done that. Then using the circuit diag check each stage cathode and other items to be grounded has a ground wire run back to that tag. That tag is then wired to chassis earth via the 10R//cap.

The PCB construction will be something of a hybrid with some higher current points (such as black speaker posts) wired directly to the grounding point and some lower level grounds connected through the PCB ground track in what is really something of an earth bus. Earth buses rely on connecting items in specific order (highest earth currents nearest the earthy point) so have a short read-up or just star wire all points back.

[Audiophill]

Thanks Richard, Greg is helping me with the schematic and parts list thanks, posted a request and he responded quickly. I will check out as you said and fingers crossed will get there.
Many thanks again
Phill

[Audiophill]

Originally Posted by John Caswell

So how is your input signal screen going to get grounded? Initially ground it at both ends, you can always cut it out after.

John

Hi John,input signal screens are also the negative of the input and I thought connected to ground at one end only to stop ground loops?

[Audiophill]

Received schematics and parts list which will help a lot( thanks Greg).

[Greg.]

Slightly off topic but studying your photo’s it appears you have paper in oil coupling caps (the gold ones) fitted. Given that we’ve established your transformers we’re wound in 2005, these caps are potentially 17 years old. These capacitors are known to become both electrically and sometimes physically leaky with age. I would be very inclined to replace them as a matter of course. New PIO caps are available if you like their sound or you could consider polypropylene or polyester.

[Audiophill]

Originally Posted by Greg.

Slightly off topic but studying your photo’s it appears you have paper in oil coupling caps (the gold ones) fitted. Given that we’ve established your transformers we’re wound in 2005, these caps are potentially 17 years old. These capacitors are known to become both electrically and sometimes physically leaky with age. I would be very inclined to replace them as a matter of course. New PIO caps are available if you like their sound or you could consider polypropylene or polyester.

Hi Greg, have just replaced with polypropylene caps, I think I will replace the electrolytic as well just in case
Many thanks Phill

[Paul Barker]

Originally Posted by Audiophill

Hi John,input signal screens are also the negative of the input and I thought connected to ground at one end only to stop ground loops?

No, youve disconnected youre ground, cables with screen can be lifted at one end if there is an internal ground wire and the screen is just a screen not a conductor. But a phono socket doesn't have surplus connectors so youre noise is probably the lack of earth coming in.

Youre confusion might come from screened power supplies and speaker cables, and fancy power leads, then you may connect one end only if its a screen alone and not a conductor. Suposedly it ruduces capacitance so might allow more high’s.

To me this is first thing to try, earth screen at both ends as John advised.

[Audiophill]

Problem solved, I replaced all capacitors and whilst checking all components found a few loose solder joints and one faulty resistor as the original builder had used 1/4watt instead of 1/2 watt ,so replaced all, now I only get a very slight hum when volume turned right up with source plugged in but think this is normal. Sounding really fantastic, like to thank all for their help!

[Greg.]

Excellent outcome. Well done Phill