Home » Audio » General » Eico HF85... "persistent hum"
Eico HF85... "persistent hum" [message #26624] Sat, 23 June 2007 08:47 Go to next message
kraken is currently offline  kraken
Messages: 6
Registered: May 2009
Esquire
Hi,

My teck and I tried to fix this "hum" sound particularily present on phono. It still present thru music on auxiliary.
All the caps has good resistance, all the tubes are ok. We just cannot find from where it's comming!

Is somebody around know what i'm talking about?
Any tricks to find out?


Thanks an have a nice day!

Re: Eico HF85... "persistent hum" [message #26628 is a reply to message #26624] Mon, 25 June 2007 17:18 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18793
Registered: January 2001
Illuminati (33rd Degree)

Disconnect the output from the HF85. Is the hum still there? If so, it's the amp, not the preamp.

Now disconnect the input to the HF85. Is the hum still there? If so, then it may be power supply hum or something else internal to the HF85. If not, it's the source. Check your ground, cables and source equipment.

Grounding problems are very common, so make sure your ground is good.


Re: Eico HF85... "persistent hum" [message #26631 is a reply to message #26628] Fri, 29 June 2007 12:14 Go to previous messageGo to next message
kraken is currently offline  kraken
Messages: 6
Registered: May 2009
Esquire
Thank you Wayne,

The problem belong to the Eico preamp. My tech try to ground everywhere he should but never obtain results.
Power supply then!... (gosh!)

I hardly dont understand these ground problem on old appliances. With no electric ground (two prong plug) and no attach to the ground anywhere, how ground can be good? There is black wires attach to the body, yes, but is that sufficient?
How could I be sure ground is good?!

Thanks again

Re: Eico HF85... "persistent hum" [message #26634 is a reply to message #26631] Sun, 01 July 2007 13:33 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18793
Registered: January 2001
Illuminati (33rd Degree)

You want a single point ground. If the main amp is grounded with chassis connected to the earth wire (third prong), then simply connect the chassis of the preamp and source components to the power amp. Measure the chassis of each with a meter first, because you want to make sure they are floating and not connected to the power line.


Re: Eico HF85... "persistent hum" [message #26635 is a reply to message #26634] Sun, 01 July 2007 14:26 Go to previous messageGo to next message
kraken is currently offline  kraken
Messages: 6
Registered: May 2009
Esquire
Thank you Wayne,
Because all of these vintage comes with two prong should we always modify them with 3 prong cord?

Just to make no mistake, from what point to point do I have to measure the chassis? (from the chassis to the eventual 3th wire prong?)
I just want to be sure of what i'm doing because I remember an old radio I had... I was unable to touch it... electrifying!

My source is a recent CD player. Should I wire the chassis to the amp too?

Thanks again

Re: Eico HF85... "persistent hum" [message #26636 is a reply to message #26635] Thu, 05 July 2007 22:16 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18793
Registered: January 2001
Illuminati (33rd Degree)

You'll need to do some measurements to know what to do. Only if the chassis floats can you ground it. If you're not familiar with this, you probably should consult a repair technician.


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