Unbalanced OT primary to CT

[dude]

I have an AO-43 Hammond OT, the Primary to CT resistance is off by about 15%, (212 ohm, 185 ohms). OT plays ok on low volume but turning up gain and volume, not much, I get unwanted distortion. Could be lots of reasons but could an unbalance OT be one of them. Amp is an 18 watt Super lite, EL-84's.

[DeepBias]

VERY common, and not a problem at all. Output transformer does not work by resistance, it transforms impedance. DC resistance has little bearing on AC resistance or impedance. It can vary DC resistance wise up to 20% and be normal.
 

[mountainhick]

I have an AO-43 Hammond OT, the Primary to CT resistance is off by about 15%, (212 ohm, 185 ohms). OT plays ok on low volume but turning up gain and volume, not much, I get unwanted distortion. Could be lots of reasons but could an unbalance OT be one of them. Amp is an 18 watt Super lite, EL-84's.

My understanding is that these transformer's windings are one coil on top of the other. As more wire is wound, the "diameter" increases, so the external one needs more wire for an equal number of turns. The induction is balanced by virtue of winding ratio. The resistance is umbalanced by virue of of the outer coil being a longer length of wire to achieve same turn ratio.

[kagliostro]

Correct

There was an old trick to solve the problem (used in OT), assuming the construction of the primay of a PP OT, instead to wind the two semi windings one over the other, the trick was to wind the primay using paired wires and use one wire for the first semiwinding and the other wire for the other semiwinding

Franco

[dude]

Well, a 15% difference isn't much and mountianhick's answer "winding over the first primary winding" makes sense. The distortion was circuit was jammed into small chassis, AO-35 chassis, fixed with shielded input wires.
Sounds ok now, I have some hum or blow/by but grid wires run close to plate wires, lead dress helped a lot, just an 18 watt Super Lite (TMB) jammed into an AO-35 is very tight. I had to used the Hammond upright old cone bd, so difficult to address lead dress, I'm happy.
Thanks, all.