Hi Tom.
In brief, if you wish to set to original playback level.
adjust replay level to Approx +3 vu.
However that standard is the original Ampex operating level.
Dating back to the early 1960's.
Tape stock improved greatly over the years.
In the last days of professional recording always being done on tape.
Ampex and other manufactures produced tape stock that could record at operating level 9 db above "Ampex"spec'
And still maintenance same distortion figures, but increasing signal to noise level to a point to compete with Digital recorders .
For machines like B77 , pr 99 etc . They should be able to operate at 250 nW at 7.5 i.p.s.
Problem will be record drive and or Head saturation in record. So you loose front end on any sudden transient.
I use to have to do the calculation to convert test tape level to desired operational level all the time.
You can calculate the db difference in the same manner you calculate the difference in voltage.
20 × log (Flux ratio)
20 x log(185/250) =2.61db.
I think I would be trying to get machine to record at 250 nW/m if I was in your situation.
Just one question, if you play back the test note, adjusted back to 0 VU, is it distorted ?
I think I had some machines, that the replay head would distort, in my case 320 nW/m .
I that case for me, the tape machine was not suitable for the task required.
For you, just go back to manufacturer spec.
I hope that help somewhat.
Des
