eddy currents, rusty laminates... say what?

jhundt · May 5th, 2008, 12:44 PM

I just read the 'back-page Shop Talk' article in my May 2008 Guitar Player magazine. There was Gerald Weber saying that if your power transformer had rusty laminates it would cause eddy currents which would rob power from all of your circuits.

Well I immediately had to check, so I followed his directions and measured for conductivity across the laminates on my '55 5E3 Deluxe. Well, sure enough, I must have some serious power-robbing eddy currents because my laminates were completely conductive.

Funny enough, we used that amp a few months ago for a jam session; it was turned on and in use for over 4 hours. Angelo (aka AngelStrummer) played through the amp for the whole session and thought it sounded fine.

Has anyone else ever heard of these mysterious eddy currents? Is this for real?

Gerald was a big help for me back in the 90's, but sometimes I wonder if he's freaking out about some things. He also wrote that my amps wouldn't work well in Europe because the 50-cycle current would "saturate" the transformers. He never explained what that saturation would actually do, and after 8 years here I still can't figure out what he meant.

Billm · May 5th, 2008, 01:37 PM

It's true that the plates should be electrically insulated from one another for maximum transformer efficiency. In the old days they used varnish; now they use a thin oxide film. When the plates rust, the whiskers of rust pierce the coating and make conduction paths from plate to plate. There's not much you can do about it. With conduction between the plates the transformers might be running a bit warmer, might be saturating a bit earlier.

Wire brushing and refinishing transformers is generally regarded as a bad idea that makes things worse.

But if your amp sounds good, ignore it.

jhundt · May 5th, 2008, 02:27 PM

Quote:

With conduction between the plates the transformers might be running a bit warmer, might be saturating a bit earlier.

thanks for the reply, Billm. I'm still wondering what "saturation" means in terms of my transformers - is it something I will hear?

Billm · May 5th, 2008, 04:10 PM

Saturation means that the core can't get any more magnetized by the incoming signal. And thus it can't impart any more signal strength to the outgoing signal. Eddy currents are wasted areas of magnetization that can't pass signal along to the output.

Dacious · May 5th, 2008, 07:57 PM

If the amp does not sound bad, I would not be too concerned. Paint the exposed rusty areas with some rust conversion paint to hinder it's progress.

Eddy currents can show up as noise almost like radio interference. If you haven't got that rest easy. I have one transformer that had surface rust - I just brushed off the loose stuff with a soft brush and painted it. It is still OK years later. An armature or transformer winder can take them apart, clean and relacquer them if it gets bad.

celeste · May 6th, 2008, 01:57 PM

The eddy currents are a big enough deal that they use special alloys for the laminations. the silicon in the steel makes it less conductive and so smaller eddy currents. Then you make the "lams" isolated from each other to further reduce conductivity.

In really cheep power transformers, like microwave ovens, you find that keeping the "lams" from rattling was of more importance then eddy currents, they weld the lams together. So you see, it ia mostly a mattter of priorities.

May 5th, 2008, 12:44 PM	#1 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 2,735 9 Photos	eddy currents, rusty laminates... say what? I just read the 'back-page Shop Talk' article in my May 2008 Guitar Player magazine. There was Gerald Weber saying that if your power transformer had rusty laminates it would cause eddy currents which would rob power from all of your circuits. Well I immediately had to check, so I followed his directions and measured for conductivity across the laminates on my '55 5E3 Deluxe. Well, sure enough, I must have some serious power-robbing eddy currents because my laminates were completely conductive. Funny enough, we used that amp a few months ago for a jam session; it was turned on and in use for over 4 hours. Angelo (aka AngelStrummer) played through the amp for the whole session and thought it sounded fine. Has anyone else ever heard of these mysterious eddy currents? Is this for real? Gerald was a big help for me back in the 90's, but sometimes I wonder if he's freaking out about some things. He also wrote that my amps wouldn't work well in Europe because the 50-cycle current would "saturate" the transformers. He never explained what that saturation would actually do, and after 8 years here I still can't figure out what he meant.

May 5th, 2008, 07:57 PM	#5 (permalink)
Dacious Friend of Leo's Join Date: Mar 2003 Location: Godzone Posts: 2,605 35 Photos	If the amp does not sound bad, I would not be too concerned. Paint the exposed rusty areas with some rust conversion paint to hinder it's progress. Eddy currents can show up as noise almost like radio interference. If you haven't got that rest easy. I have one transformer that had surface rust - I just brushed off the loose stuff with a soft brush and painted it. It is still OK years later. An armature or transformer winder can take them apart, clean and relacquer them if it gets bad. __________________ My other Telecaster is a Thinline The Tele Bible, Ch 1, v 10 Love thy Telecaster, covet not thy neighbour's Strat!

May 5th, 2008, 01:37 PM	#2 (permalink)
Billm Tele-Meister Join Date: Mar 2008 Location: New Jersey Age: 61 Posts: 252	It's true that the plates should be electrically insulated from one another for maximum transformer efficiency. In the old days they used varnish; now they use a thin oxide film. When the plates rust, the whiskers of rust pierce the coating and make conduction paths from plate to plate. There's not much you can do about it. With conduction between the plates the transformers might be running a bit warmer, might be saturating a bit earlier. Wire brushing and refinishing transformers is generally regarded as a bad idea that makes things worse. But if your amp sounds good, ignore it.

May 5th, 2008, 04:10 PM	#4 (permalink)
Billm Tele-Meister Join Date: Mar 2008 Location: New Jersey Age: 61 Posts: 252	Saturation means that the core can't get any more magnetized by the incoming signal. And thus it can't impart any more signal strength to the outgoing signal. Eddy currents are wasted areas of magnetization that can't pass signal along to the output.

May 6th, 2008, 01:57 PM	#6 (permalink)
celeste Tele-Meister Join Date: Jun 2006 Location: Maryland Age: 46 Posts: 217 12 Photos	The eddy currents are a big enough deal that they use special alloys for the laminations. the silicon in the steel makes it less conductive and so smaller eddy currents. Then you make the "lams" isolated from each other to further reduce conductivity. In really cheep power transformers, like microwave ovens, you find that keeping the "lams" from rattling was of more importance then eddy currents, they weld the lams together. So you see, it ia mostly a mattter of priorities.