Just finished up wiring on a Hey What 504.  Slowly applied power with variac no smoke.  Hearing a strange buzzing out of the OT.  When I hook a speaker i hear loud squealing from speaker.  I'm assuming oscillation.  When I disconnect the to input wires from the phase splitter from the out put tag board it all quits.  No sound from the OT.  Wiring diagram leaves alot to be desired!  Does this design use grid stopper resistors?  I have one small black wire from the output tag board at the end where the OT sits.  It is not connected and am wondering if it might be the feedback connection.  I can send picks if needed.  This came half wired and I'm finishing. 

Hey,

The squealing sound may be due to having the OT primaries at the power tubes swapped! When building an amp there is always a 50% chance to get that wrong and the outcome is a high pitch squealing sound on startup! In other words swap the blue and red wires at pin 3 on the EL34's then power up again!
Make sure not to power amp up without the speakers connected, will take out the OT!

Todd