My current restoration project, a Marconi Model 187, has an intermittent "buzzing" that emanates from inside the power transformer. If I push on the wires where they exit the transformer the buzzing stops, but returns after a few minutes. This indicates the problem is mechanical in nature. The radio plays great and all voltages are right on. The transformer runs at, what I would consider, normal temperature.

I will be removing the transformers to investigate this phenomenon.

However, I do remember a post on this some time ago. Has anyone experienced this? Aside from tightening the screws, what else can be done to eliminate the buzz.

Gary

Kinda sounds like the core laminations are loose and buzzing when you apply power. As power is applied, magnetic flux flows around the core and can force same polarity laminations apart. Does it sound like a 120hz buzz? See if it's possible to tighten the screws or bolts holding the laminations together.
Steve

If tightening doesn't help, perhaps the transformer laminations could use some coating to dampened the vibrations. GC Electronics has a corona dope that might work. It will take high temps. See: http://www.gcelectronics.com/order/Catalog_PDF/2007%20Catalog%20120407%2056.pdf
Rather pricey though.
Steve

I managed to remove the bolts and top cover without disconnecting the xfmr. As suspected, the laminations were loose. Upon close inspection I noticed that one of the bolts was stripped. So a couple of new bolts, star washers and nuts all tightend up eliminated the buzzing. I even bolts with "Robertson" heads. This gives the restoration a bit of a Canadian signature.

Gary

:Kinda sounds like the core laminations are loose and buzzing when you apply power. As power is applied, magnetic flux flows around the core and can force same polarity laminations apart. Does it sound like a 120hz buzz? See if it's possible to tighten the screws or bolts holding the laminations together.
:Steve

:I even bolts with "Robertson" heads. This gives the restoration a bit of a Canadian signature.
:
:Gary

Yeah ! Way to go Gary!

Syl - from Québec

::I even bolts with "Robertson" heads. This gives the restoration a bit of a Canadian signature.
::
::Gary
:
:Yeah ! Way to go Gary!
:
:Syl - from Québec
Could you explain "Robertson" heads for those of us who are Canadian challenged?

Bill from D.C. (not B.C.)

Yes please... you can even say it in Canadian.

:Could you explain "Robertson" heads for those of us who are Canadian challenged?
:
:Bill from D.C. (not B.C.)

I find it odd you've never head of Robertson heads. I suspect you've seen them but never knew the real name.

The best fastening system on earth.

http://www.robertsonscrew.com/

Syl

::Could you explain "Robertson" heads for those of us who are Canadian challenged?
::
::Bill from D.C. (not B.C.)
:
:I find it odd you've never head of Robertson heads. I suspect you've seen them but never knew the real name.
:
:The best fastening system on earth.
:
:http://www.robertsonscrew.com/
:
:Syl
Hi Zyl,
I see it now, a square driver fitting into a square hole on the screw. I have a driver in a set of bits, but have never seen a screw.
I didn't think I was that far from Toronto. I listen to CHWO every night.

Best Regards,

Bill Grimm

I've seen these on decking screws and thought it was just the manufacturer making his screws unique. Like my competitor's product is a nail while my product is an inter-fiberous friction fastener. PL

:::Could you explain "Robertson" heads for those of us who are Canadian challenged?
:::
:::Bill from D.C. (not B.C.)
::
::I find it odd you've never head of Robertson heads. I suspect you've seen them but never knew the real name.
::
::The best fastening system on earth.
::
::http://www.robertsonscrew.com/
::
::Syl
:Hi Zyl,
: I see it now, a square driver fitting into a square hole on the screw. I have a driver in a set of bits, but have never seen a screw.
: I didn't think I was that far from Toronto. I listen to CHWO every night.
:
:Best Regards,
:
:Bill Grimm