PT laminations are usable as OT laminations ?

[Kagliostro]

I've a pair of unknown transformers (250/350W) in very good shape, I think they were recovered from a pair of inverter Power Supply (so unknown and probably unusable voltage ratings)

I've also some old PT that are in bad shape (and must bee rewound as to be usable)

I'm wondering if the laminations of this transformers are usable to build bass and/or guitar OT (I need big OT as to use some GU50 tubes I've)

Thanks

K

[Diablo1]

Yes, you can use the laminations from your PT to build an OT and vice versa. There are different grades and gauges of steel that have been used for PT and OT laminations. Lots of choices, and really any of them can be made to work depending on how many amp-turns are going to be put through the windings. The idea is to keep the transformer from being driven so hard that you magnetically saturate the laminations.

[Kagliostro]

Thanks for your contribute

K

[roberto]

The idea is to keep the transformer from being driven so hard that you magnetically saturate the laminations.

Or just on the edge.

[Cliff Schecht]

Typically the difference between a power transformer and output transformer is the quality and thickness of the laminations. Since a power transformer only has to handle 50/60 Hz, the laminations can be made relatively fat and out of cheaper non grain aligned steels without suffering from excessive eddy current losses. An output transformer, on the other hand, usually uses much thinner yet high quality steels which allow for much higher frequencies to permeate through the core at high energy levels without suffering from excessive losses.

So with that said, power transformers will saturate easily if you try to apply a lot of power through them at higher frequencies. If you keep the power levels low for the size of the output transformer like how others mentioned however, saturation won't be a problem. However, at the power levels you'll be dealing with using even a pair of those GU50's, I don't think the laminates from a power transformer will make a very good output transformer. Plus there are different winding techniques that will play a big role in how the output transformer sounds..

[katopan]

I've used PT laminations in an OT I wound myself. Good enough for guitar. Not a lot of high frequencies and normally way oversize for power to get enough bass response from a high enough primary inductance (unless it's a puny Fender OT or something). Although that was for a 10W amp, and as Cliff said the extra losses may not be good for an OT as big as what you're talking about.

[Diablo1]

You might see anything between M19 and M6 steel in typical production OTs.
M6 is fairly common for PTs.
M6 is a grain oriented steel, and M19 is a non-oriented steel.
Take a micrometer and measure the thickness of one of your laminations and you may be able to determine what type of steel it is.
Thinner lamninations in general will have lower core losses and that means the transformer will stay cooler. By using better steel (M6 or other grain oriented) the manufacturer can reduce the amount of steel in the transformer. Nothing stops you from making an extra large transformer that uses more of the "good" steel. This combo will keep the transformer from saturating, and that means the frequency response will not be attenuated for guitar. Larger transformers also stay cooler for the same power output.

[Kagliostro]

Many thanks for the infos

K