Hum problem....

[Chris]

Am still trying to understand why there is no hum when the Cd player is playing music, but once it is stopped the hum occurs? and very loud.
Wednesday I will have a little time to explore more.

Chris

[Richard]

Originally Posted by Chris

Am still trying to understand why there is no hum when the Cd player is playing music, but once it is stopped the hum occurs? and very loud.
Wednesday I will have a little time to explore more.

Chris

Hi Chris, only guessing and just to this point, it may be that the CDp output impedance is very low when powered up / playing music and is similar to the shorting plugs. When not powered it may effectively be an open circuit. Try it connected to the inputs, and powered up, but not playing music.
That said I think something else is going on.

[bob orbell]

I yesterday visited the guy who has my 6550, remembering the issue Chris has, I asked him to power it up, a very gentle hum connected to Pre III, disconnected, ditto, clearly, something amiss with Chris's amp. Bob

[John Caswell]

Hi all,
There is something not making sense here.
Try this, amp off, remove just one ECF80 and leave inputs open ie no shorting plugs. Remove L/S on the ECF80 channel and fit an 8-10R resistor across the L/S terminals Then power up, no damage will occur as the ECF80 is capacitor coupled to the 6550.
Does it hum on the non ECF80 channel? Repeat the exercise on the other channel, then report back

John

[bob orbell]

Come on Chris, we are all waiting for the results, this problem puzzles me. Bob

[Chris]

Hi Bob, John and Richard

Will have a couple of hours today to check over the amp for basic issues, I have bought a new earth pillar and some lug ring crimps, where I can fix with out soldering.
I did fit a copper band around one output transformer, need to put plastic washer under the bell cover as there is continuity between the cover and copper band (could be the issue), will also earth the output transformers to connecting nut with a wire.
But will concentrate on safety earthing first, so all connections are secure and arrange neatly, will use similar gauge ground earth as mains cable, most of this is just rework, but is better to do now.

Chris

https://www.ebay.co.uk/itm/Cliff-TP6...72.m2749.l2649

[bob orbell]

I would suggest you follow Johns test, this should eliminate or confirm a problem with phase splitter/input or power side of the amp. Bob

[Chris]

Will do Bob, just making tidy the Ground earth to the chassis and then to the new Earth pillar and will connect the Star Earth to the pillar.

"L/S" is that left side, lead side?


Chris

[bob orbell]

Loud Speaker. Bob

[Chris]

Thanks Bob, I have now established a new mains ground point between the earth post and mains inlet, using locking washers and two nuts (removing paint where the washer is held in place). So the amp has a secure to ground connection that can not be easily disconnect by accident, then from there to the new pillar post.

Chris