Blues Jr. OT upgrade

[jacklickson]

OK, feel free to make fun of the new guy as I freely admit I'm an idiot. I changed the OT in my Blues Jr. to a direct retrofit Hammond 1750F - direct replacement for the Fender part #. I change it out, turn the sucker on, and it makes the most g_d-awful squealing noise I have ever heard and scares the crap out of my kid before I can turn it off. I put all the leads in the same places they were - I took detailed notes and took photos. What did I do wrong? Was I supposed to use a variac to fire it up? Help please, but be nice - it's Easter

[Zung]

Probably not your fault, but the polarity of the OT is wrong, and your amp is oscillating. Swap the leads to the speakers - I mean, reverse them, "hot" should be "ground" and "ground" should be "hot".

[Enzo]

Not the leads to the speaker, but the output transformer leads. Typically we reverse the blue and brown wires going to the power tube plates.

[jacklickson]

Thank you!!!!

Wow guys, thanks SO much!!!! That is exactly what it was - the blue and brown wire. I really appreciate your help - thanks for taking the time to help out a new guy. All the best, JL