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McIntosh C-20 - Hummmmm

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Anonymous
January 14, 2005 8:43:37 PM

Archived from groups: rec.audio.pro (More info?)

Readers:

I have a good bit of low frequency hum in all of my phono and tape outputs
on an early 60's McIntosh C-20 preamp. The ground from the phono is
connected and, interestingly enough, I even have the hum on all outputs even
if there is nothing connected to that input.

Is this to be expected? Is it common, unavoidable, a tube problem? If
anyone has an answer, or even a decent guess, I would certainly appreciate a
lead.

Thanks in advance, MSK

More about : mcintosh hummmmm

Anonymous
January 15, 2005 12:00:00 AM

Archived from groups: rec.audio.pro (More info?)

Michael S. Kakuk <mkakuk@kakuk.com> wrote:
>
>I have a good bit of low frequency hum in all of my phono and tape outputs
>on an early 60's McIntosh C-20 preamp. The ground from the phono is
>connected and, interestingly enough, I even have the hum on all outputs even
>if there is nothing connected to that input.

How much hum is on the B+ line?

>Is this to be expected? Is it common, unavoidable, a tube problem? If
>anyone has an answer, or even a decent guess, I would certainly appreciate a
>lead.

If the hum is common to both channels, it's almost certainly bad filter
caps. If the hum on the B+ line is within the manual spec and the added
decoupling caps on each stage are good, it may be due to tubes with high
heater-cathode leakage problems.

But if the supply can caps are original, they are almost certainly bad by
now. The tubes in these units will outlast the caps.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
January 15, 2005 4:04:40 AM

Archived from groups: rec.audio.pro (More info?)

Are any components that are connected to the preamp
connected to TV cable (possibly a new aquisition DVD
player/VCR, PVR, TIVO)? If so, disconnect the TV cable from
that component and see if the hum goes away. If the hum goes
away, you'll have to put a ground loop buster in the cable
line. (Two back-to-back 75/300 ohm baluns will work). If the
hum doesn't go away, it's something else.

If you don't have TV cable hooked up to anything, it must be
something else.

It's always something...


TM

"Michael S. Kakuk" wrote:
>
> I have a good bit of low frequency hum in all of my phono and tape outputs
> on an early 60's McIntosh C-20 preamp. The ground from the phono is
> connected and, interestingly enough, I even have the hum on all outputs even
> if there is nothing connected to that input.
Anonymous
January 18, 2005 5:51:07 AM

Archived from groups: rec.audio.pro (More info?)

What a pleasure to see a posting about a Macintosh not referring to a
computer. (No insult to Apple--just a complement to a fine component)
!