PP OT to SE OT - Question

[kagliostro]

Assuming to have a PP OT that has an impedence of 4K aa and wanting to use it in a SE amp

is possible to use it if laminations are dismanted and newly mounted for the SE use (all E together & all I together)

and B+ is connected to one of the extremities of the primary

CT not connected and the other extremity is connected to the Plate of the Power Tube ?

Are problems to be expected due to the fact that the two semi primaries windins are winded in opposite way ?

Thanks

Franco

[PRR]

It will "work".

How well is not clear.

Try it.

[kagliostro]

Many Thanks PRR

Franco

[drgonzonm]

Franco,
I agree with your approach. 
It is my understanding that a few PP OTs of the EI type have the Es and the Is stacked intermixed.  that is one layer would be EI and the next layer IE(E reversed). 

By unmixing and restacking the Es and the Is, one could "gap" one outside leg of the E and create a SE OT, sometimes restacking all Es and Is, in the same direction will provide enough gap, as the reassembly is not as tight as a factory assembled transformer.  I have found a post or two suggesting creating the gap with a hacksaw. 

The purpose of the gap is to reduce saturation of the DC component when used in a SE application. 

Drgonzo

[Tony Bones]

It would work. You can even experiment with the gap if you need to, though 2 to 3 layers of post-it note would probably work well enough as a gap.

Having said that, it's a lot more difficult than you might expect to get the laminations out with damaging them. You'll almost certainly mangle the first few, which isn't necessarily a big deal. Don't bother trying to straighten them; just toss them out. The rest will have bits of paint around the edges that you can scrape off.

There will be a fine layer of dust covering the flat surfaces of the lams. Don't remove it. The purpose of it is to reduce electrical conductivity between the laminations and thus restrict eddy currents, which is the whole reason for using thin laminations instead of a solid hunk of steal.

Good luck!

[Joel]

If you have a 10W PP OPT and want to make it a 10W SE OPT, the core would be very undersized with much lower inductance than needed for decent low frequency response.

If you have a 15W PP OPT and turn it into a 5W OPT, you might be OK from a frequency response perspective.

The 'air gap' does not need to be very big.  I used one piece of note paper between the E's and I's on my last OPT.  The core was from a 15VA power transformer I re-purposed into a 5W OPT. 

[kagliostro]

I'm thinking about this mod on a Paso Line Transformer I've

it is small but labeled till 32W,  was thinking for a 10-12W SE

but I must give a close look to laminations before to try to mod it

because if there is too much "lacquer/shellac" it will be difficult to mod it

without damage some laminations

Thanks for the answer

Franco

[Tony Bones]

Just for reference, the stack of laminations for a 10W - 12W SE output transformer would need to be in the neighborhood of 3" x 3.5" and 1" to 1.5" thick. I've never seen a line transformer that large...

[kagliostro]

Yes, you are right, at the moment I haven't the transformer under hand, but it isn't so large

May be enough for an 8W (may be)

Franco

[drgonzonm]

at http://geofex.com/, there is an article dated 7/18/13; that shows a disassembly of a small transformer.   Experimental transformer salvaging stuff,

[kagliostro]

Thanks

Franco