Universal Audio LA3a OPT

weird circuit, weird transformer, all bi-fi, but one bi-fi wind has two different wire sizes ,  only time i have seen this,

has a DC balance coil  that is connected out of phase that handles about 10 ma,    do not know how much current is going the other way thru the pre-driver transistor,

no take down just a print,

fyi  LA3a schemo>

> one bi-fi wind has two different wire sizes ,  only time i have seen this

Odd but makes sense. Brn-Red is in series with signal, should have low DCR. Yel-Org does not deliver signal anywhere and is in series with a very large resistor. Ideally Yel-Org would have 2,600r DCR, so about #55 wire. But nobody could find the end of #55 wire, so they used something they could handle and shimmed it out with a resistor. (Uh, actually, no, it has to be <2600r but the exact value is not real critical; maybe #37 was on sale that day.)

> has a DC balance coil  that is connected out of phase that handles about 10 ma,    do not know how much current is going the other way thru the pre-driver transistor

Thanks PRR!

Cj it looks like you've swapped the wire gauges on the bottom of the print

we done fixed that, thanks! 

Hi CJ

The TX is a magnetic amplifier (or known as a "mag amp"). The bias in the DC winding changes the coupling.
Duke