Transformer secondary resistance

Can I get an approximate output value of a transformer based on secondary resistance? I have a Korg line mixer. The primary windinding weathered away and I can't access it. resistance on the secondaries is 3.7 to center tap for each lead. I found one in a CD player that seems to work but I don't know the voltage of the original. I am near certain that the transformer I tried is a little on the weak side.


Paid Member
2007-09-15 8:14 am
The secondary resistance has no real relationship to the voltage. 3.7 ohms could be many turns of thin wire or less turns of a thicker wire. Both would be 3.7 ohms, one giving (say) 20 volts AC and the other 6 volts AC.
That was very intuitive. That link answered quite a few questions. On my other desk I currently have some Older dynaudio drivers and bits and pieces of amplifier, crossover and power supply. Seeing that Dynaudio has followed every other Brand and their trends, I am glad that I opted against buying a pair. 10 years ago, Dynaudio Studio monitors were great but they are beginning to look like overpriced MP3 monitors like the Blue Skys I just sold.
Thank God for this forum! It makes true Hi fidelty attainable. I am also learning how to fix the broken stuff to keep the LoFi neighbors happy.
I look at the regulators and OP amps if I don't have schematic?
Way to go.
That and power consumption.

Measured resistance can be used at most to distinguish "which is which" , and even so, it can still mislead you.
Say, you have a transformer for a small tube amp (say, a Champ), the HV winding will have, say, over 60 or 120 ohms DCR while the filament one less than 1 ohm.
Piece of cake :)

Now you have a transformer for a big SS amp: 40+40VAC for the main power amp, and 15+15V for the preamp.
The 80V winding will usually have *less* resistance than the 30V one :eek: , simply because the first one will be required to furnish, say, 5 to 10A while the second one may be happy with 100 mA.

And as a side note, low resistances are difficult to measure with precision ... unless you have a bridge or a dedicated meter.