I'm crunching the numbers on transformers suitable for an EL34 based 30W amp (gee, let me think, maybe an Express?
![Wink :wink:](./images/smilies/icon_wink.gif)
I'm using old iron I have in a junk box - no lamination specs or any way of really measuring B-H curves, etc. So I'm relying on rule of thumb calculations I've been taught elsewhere and 'reality checks' against advertised transformers. You can calculate flux and everything in detail, but all that goes out the window if you don't have lam curves and know that what you've got will actually perform to them. So I've got donor iron and one spool of wire of the right size already. Probably need 3 other wire sizes - for all up a bit over $100 (and quite a few hours) for both PT & OT I think I can live with very good but not clone identical tone.
![Very Happy :D](./images/smilies/icon_biggrin.gif)
So for some general specs to get the ball rolling...
OT: 6k6 p-p primary, 4/8/16 secondaries, 30W rating, and the Express OTs I can find listed on other sites have US Ei-125 lams.
PT: I'm in Oz so primary will be 240V. 3 preamp valves and 2 EL34s needs 250mA, and if I want to use the iron for something 6L6 based in the future it won't draw as much as the EL34s, so secondary 1 will be 300-0-300V at 250mA. Likewise EL34s are more heater hungry, and with 3 preamp valves the total heater current is just under 4A. I'll design for at least 4.5A depending on wire size, so secondary 2 is 6.3V at 4.5A+. Other sites have US Ei-125 lams for the PT too but with a really big stack height.