I Have an old music(nostalgic)audio tape which i recorded about 1977 in a club. I’ve managed to transfer it to audacity but how do I adjust the tracks so they have the same output level.
mickthefish.
PS.One tracks ok at -3DB but other is really low. 
You’re talking about left & right balance? Is it actually a stereo recording or is left & right the same (other than the levels)?
The Normalize effect has an option of normalizing the left & right channels independently. That will make the left & right peaks equal.
Peak levels don’t always correlate well with perceived loudness and it may not sound balanced after normalizing the peaks. In that case, click the little drop-down arrow to the left of the waveform and click Split Stereo Track. That will allow you to select and adjust the tracks individually. Use Amplify effect to adjust the volume up or down. If you’ve already normalized you’ll probably need to lower the louder channel (using a negative dB Amplify value) rather than boosting the quiet-sounding channel… If you push the peaks over 0dB you can get clipping (distortion) when you export and play back.
If you need a lot of boost, noise may become a problem (because the noise gets amplified too). In that case it may be better throw-away the weak-noisy channel. The same drop-down arrow menu has a Split To Mono option. After splitting to mono, you can delete the weak-noisy channel and a mono recording will play-back through both speakers.